The Mast Cell Connection Nobody's Talking About
If you've ever been told you're "too sensitive" to perfume, cleaning products, or jet fuel — or watched your child fall apart in a scented hotel room and been dismissed as overreacting — this episode is going to change the way you understand what's actually happening in your body.
Haylie Pomroy sits down with Dr. Theoharis Theoharides, Professor of Clinical Immunology, Executive Director of the Center for Excellence in Neuroinflammation Research, and Director of the Institute for Neuro-Immune Medicine-Clearwater, for one of the most clinically rich and personally candid conversations on the show. The topic: multiple chemical sensitivity (MCS), mast cell activation, and the science that finally validates what so many patients have been told is "all in their head."
What Is Multiple Chemical Sensitivity?
Multiple chemical sensitivity — also known as idiopathic environmental illness — is a complex set of symptoms that develop after exposure to even tiny amounts of various environmental substances. The list of triggers is long: benzene, alcohol, formaldehyde (found in wrinkle-resistant cotton clothing), preservatives and dyes in food, perfumes, cleaning products, jet fuel, fluorescent lighting, mycotoxins from mold.
"Because they're such complicated and multiple triggers, and because people have symptoms even to tiny amounts, many colleagues unfortunately don't believe that this is a real problem," Dr. Theoharides explains.
There is currently no diagnostic code for MCS in the United States. Patients who present with multiple symptoms and sensitivities are often sent to allergists, who frequently dismiss the condition as non-real. Without a medical framework to hold it, patients are left without validation, without treatment, and without answers.
Dr. Theoharides's position: the code we should be using is mast cell activation, unspecified — because at the biological root of multiple chemical sensitivity is the mast cell.
The Canary in the Coal Mine
Dr. Theoharides uses a vivid image to describe people with MCS: they are the canary in the coal mine. They react to what everyone is being exposed to — they just react first and more severely.
"I dare say it has an impact on everybody. It's just that some individuals, for reasons we will discuss, are more sensitive, and therefore more likely to have both severe symptoms and chronic sequelae of the problem."
Haylie shares her own story. She was always sensitive to perfumes and dyes as a child — would rash, react, feel sick in traffic. But it wasn't until a heavy malathion exposure in California that her immune system was pushed over the edge, triggering her ITP diagnosis. Looking back, she can now trace the line between chemical exposure, immune response, and the onset of her autoimmune disorder.
This is more common than most people realize. Many individuals with autoimmune conditions can, when they trace backward, link the original onset to a significant environmental exposure. "We usually worry about an immediate reaction, not necessarily the chronic reactions," Dr. Theoharides notes.
What's Actually Happening in the Body
The key to understanding MCS is understanding mast cells.
Mast cells are unique immune cells that originate in the bone marrow and travel to tissues throughout the body — around blood vessels, next to nerve endings, and in every organ exposed to the outside world: the eyes, nose, mouth, lungs, skin, and gut. In the brain, they're found specifically around the blood-brain barrier and in the areas that regulate the body's core functions — the hypothalamus, hippocampus, and amygdala.
Think of a mast cell as a soccer ball filled with roughly a thousand ping-pong balls, each containing a different chemical compound. When triggered, the cell can explode — releasing the contents of all those granules, and then manufacturing another hundred or so molecules over the following six hours. Within 24 hours, it restocks itself and is ready to fire again.
Most medical treatment focuses on just two of the 300-plus molecules mast cells release: histamine and leukotrienes. "We have no idea what the others do," Dr. Theoharides says — including proteolytic enzymes like tryptase and chymase that he calls "meat tenderizers."
Mast cells can be triggered not just by the 300 or so allergens they're classically associated with — they have roughly 300 receptors on their surface and respond to chemicals, fungi, bacteria, viruses, stress, temperature changes, and even vibration. The allergic response most people are familiar with is, as Dr. Theoharides puts it, "the tip of the iceberg."
Why Stress Makes Everything Worse
Here's the piece that brings the science home for so many patients: stress dramatically lowers the threshold for mast cell activation.
When you smell something — even a perfume — that signal travels up the olfactory nerve to the hypothalamus. The hypothalamus releases a hormone called corticotropin-releasing hormone (CRH). CRH, in turn, stimulates the mast cells. So the act of smelling a potential danger resets the reactivity of your entire immune response.
"Millions of years ago, we didn't have perfumes," Dr. Theoharides explains. "We and animals would smell danger — and that's the important thing. We literally smell danger, and this danger puts us into fight-or-flight, which triggers the mast cells to orchestrate a response."
A perfume. A scented laundry detergent. Jet fuel. Your body doesn't know the difference between that and a predator. It responds accordingly.
And stress — physiological or psychological — releases that same CRH, which lowers the bar for how much exposure it takes to trigger a reaction. While you might have needed 100 units of something to set off a response under normal circumstances, under stress you might only need 10. This is why, as Haylie describes, her chemical sensitivity is dramatically worse when she's stressed or depleted — and why stress doesn't "cause" MCS so much as amplify it.
"It's not sensitivity anymore," Dr. Theoharides says. "The mast cells are activated, and they can release chemicals that cause all the problems these individuals are describing."
The Word "Sensitive" Is Misleading
One of the most powerful moments in this conversation is when Haylie pushes back on the language.
"The word sensitive sometimes makes a person feel like you could muscle through it or use your brain cognitively to just suck it up and get through it," she says. "I'm actually having an immunological response. It's not that I can't deal with it."
This reframe matters enormously for patients. MCS is not a personality trait or a character weakness. It is a measurable, physiological immune response. And the fact that not everyone reacts visibly — with hives, blistering lips, or rashes like Haylie — doesn't mean others aren't being affected. Brain fog, anxiety, depression, cognitive difficulties, and behavioral changes in children can all be manifestations of mast cell activation in response to chemical exposure. They're just harder to point to.
Testing: What to Ask For
If you suspect mast cell activation or chemical sensitivity, Dr. Theoharides recommends the following labs:
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Total IgE — to assess for classic allergic reactions
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IgG1 and IgG4 subclasses — IgG4 is responsible for food intolerance and sensitivity through mast cell receptors
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Vitamin D3 — deficiency is common and it has anti-allergic properties; he recommends 5,000 IU daily for most people
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Glutathione — the body's primary antioxidant; chemical bombardment causes oxidative stress and depletes it
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IL-6 (interleukin-6) and VEGF (vascular endothelial growth factor) — both measurable through standard labs like Quest and LabCorp, and strongly correlated with symptom severity
He also notes a simple, no-cost clinical screening: scratch the underside of the forearm in one continuous line. If the scratch turns red within two minutes, mast cell activation is likely. No allergens needed — the mechanical pressure alone triggered the response.
For environmental exposures, Dr. Theoharides also recommends measuring heavy metals (blood for recent exposure, urine for up to six months, hair for long-term) and mycotoxins in the urine — noting that roughly 50% of mycotoxin exposure comes not from moldy buildings but from food.
What Can Help
Avoid the trigger first. Once you know what activates your mast cells, removing or reducing that exposure is the most powerful first step.
Block the mast cells. Rather than trying to desensitize to every possible trigger — an approach that becomes unwieldy when there are hundreds of them — Dr. Theoharides's strategy is to block mast cell activation directly. Some natural compounds that help:
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Luteolin, a flavonoid with demonstrated mast cell-stabilizing properties. Because it isn't well absorbed from the gut in standard form, he recommends liposomal preparations made with olive oil to improve bioavailability.
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Vitamin D3 (approximately 5,000 IU daily) — anti-allergic and widely deficient even in sunny climates, because dietary vitamin D must be converted through both the liver and kidneys to become active
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Berberine — particularly useful for those exposed to mycotoxins or pathogen-derived toxins
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Glutathione — can be administered intranasally, orally, or by injection depending on the clinical situation
Restore gut health and reduce systemic inflammation first. As Haylie notes from her clinical practice, desensitization and other approaches work better once the gut is healed and the inflammatory load is reduced. The gut-brain axis is highly active, and the microbiome plays a significant role in how the immune system responds to triggers.
Track your biomarkers. Using measurable markers — IL-6, VEGF, vitamin D3, glutathione — means you can track whether your interventions are working. The body will tell you if you're heading in the right direction.
Practical Tips for Chemically Sensitive Travelers
Both Haylie and Dr. Theoharides have navigated significant chemical exposure through travel and offer practical guidance:
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Standard 3M masks do not filter odors. You need a mask with activated charcoal to block chemical smells, including jet fuel.
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Jet fuel at airports is a significant trigger for mast cell activation — be proactive before and after flights.
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Hotel sheets, carpets, and cleaning products are common exposure points. Haylie sends emails, leaves notes, and speaks to the front desk about fragrance-free accommodations. Being vocal matters — hotels use scented products because they believe customers want them.
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Take D3K2 at time of exposure — Haylie uses this as a transient immune support strategy when traveling or entering chemically loaded environments.
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Consider a travel supplement kit with beet-derived vitamin C, D3K2, and liposomal luteolin for high-exposure situations.
A Note on Mycotoxins
Dr. Theoharides closes with an important reminder: mold exposure isn't limited to water-damaged buildings. Approximately 50% of mycotoxin exposure comes from food — mold grows on food constantly, and its volatile toxins can trigger mast cell activation, neurological symptoms, and immune dysregulation.
He shared a case from Massachusetts in which a group of people became severely ill from marijuana they'd purchased legally — not from the cannabis itself, but from mold that had contaminated improperly stored inventory. Botrytis neurotoxicity. A complete psychotic break. Eventually tracked down through mycotoxin testing.
If mold exposure is suspected, urine mycotoxin testing from at least two time points within three months is recommended.
About Dr. Theoharis Theoharides
Dr. Theoharis Theoharides is a Professor and Vice Chair of Clinical Immunology and Director at the Institute for Neuro-Immune Medicine-Clearwater, and Adjunct Professor of Immunology at Tufts School of Medicine. He received his BA, MS, MPhil, PhD, and MD degrees from Yale University, where he also received the Winternitz Prize in Pathology. He has 485 publications with over 46,000 citations, an h-index of 106, is rated the worldwide expert on mast cells by Expertscape, and has been inducted into the Rare Diseases Hall of Fame and the World Academy of Sciences.
Connect with Dr. Theoharides:
About Haylie Pomroy
Haylie Pomroy is the Founder and CEO of The Haylie Pomroy Group and a New York Times bestselling author of The Fast Metabolism Diet. With over 25 years of experience in nutrition, biochemistry, and patient advocacy — and her own journey with autoimmune disease and chemical sensitivity — she brings both clinical expertise and lived experience to every conversation.
Learn more and connect with Haylie:
Transcript
Haylie Pomroy: Welcome to Fast Metabolism Matters, where we examine the scientific approach to how your metabolism influences every aspect of your life. I'm Haylie Pomroy, number one New York Times bestselling author. For the past 30 years, I have been creating a support system for vibrant health.
I was in my early 20s battling a life-threatening autoimmune disorder when I learned how vital metabolic health is to our whole being. Join me as I share these insights, and together, let's find out why having a fast metabolism matters.
Today we're going to be talking about multiple chemical sensitivity. Given the conversation that's happening right now about what all these chemicals are doing in our bodies, and what it actually means for the individual, I think this is incredibly important. I am joined by our professor of clinical immunology — the executive director of the Center for Excellence in Neuroinflammation Research. Dr. Theoharis Theoharides, thank you so much for being here with me today.
Dr. Theoharis Theoharides: It was a real pleasure to be with you once more, Haylie.
Haylie Pomroy: Your podcasts have just gone crazy — everybody loves the science that you bring to us in a way that we can apply to real life. Dr. Theoharides trained at Yale School of Medicine, holds a Doctor of Medicine and a Doctor of Philosophy in Pharmacology from Yale University, a Master's of Philosophy in Immunopharmacology and a Master's in Science in Neuroimmunology from Yale, and a Certificate of Global Leadership and Management from the Fletcher School at Tufts University — among many other credentials and honors.
What has been resonating with so many of our community members is your compassion and empathy for what they're going through, and the real-life practical data you give us to change our lives. Let's dive in. I want to talk about multiple chemical sensitivity. How would we define that?
Dr. Theoharis Theoharides: Well, it's almost impossible to define, and it's known by different names, including idiopathic environmental illness. Basically, it's a set of rather complex symptoms that develop after exposure to even tiny amounts of various environmental substances. It could be chemicals like benzene, even alcohol. It could be formaldehyde found sometimes in cotton clothes — added so they don't wrinkle. It could be preservatives and dyes found in foods. The list goes on and on.
And because there are such complicated and multiple triggers, and because people have symptoms even to tiny amounts, many colleagues unfortunately don't believe that this is a real problem.
Haylie Pomroy: When I was diagnosed with my autoimmune disorder, they were doing a lot of tracking back — looking at what had changed in my health. One of the most interesting questions they asked was whether I got carsick in traffic. They said that was sometimes an overlooked symptom in individuals with multiple chemical sensitivity.
I was always sensitive as a kid to perfumes and dyes — I would rash. But it wasn't until I got a heavy malathion exposure that I was pushed over the limit. That was the trigger for my ITP, my autoimmune disorder. After that, I knew what had pushed me over the edge and what to address.
When we talk about multiple chemical sensitivity — are these typically people who are sensitive to cigarette smoke and perfumes, who then go through the world as the canary in the coal mine once their bodies are out of balance?
Dr. Theoharis Theoharides: Well, first of all, you mentioned something very important. Individuals may have symptoms when they're exposed, but many of them also develop autoimmune problems over a period following that first exposure. Looking back, individuals with various autoimmune problems can often link the original symptoms of autoimmunity to such exposures — which is another factor that just doesn't enter into our thinking about what these exposures may do. We usually worry about an immediate reaction, not necessarily the chronic reactions.
I would definitely call them the canary in the mine. I used to travel with a lady who had multiple chemical sensitivity, and every time we went through customs — forced to walk through duty-free — she would absolutely collapse, hit by so many perfumes. There was no way around it. You literally have to wear a chemical mask.
Haylie Pomroy: Duty-free is my nightmare. I literally pack a thick sweatshirt specifically to put over my face and run through. They shouldn't be able to do that.
Dr. Theoharis Theoharides: They shouldn't. And I've written to various countries about airports and no one has ever replied. And before we go on, it's important to say that even the so-called 3M masks that became very prevalent during the pandemic — the ones that can prevent viruses — do not actually clear odors. One has to have a mask with activated charcoal in it, and there are such masks. That would be my advice for anybody who's sensitive to odors, especially jet fuel. Whenever we get to an airport, you smell jet fuel no matter where you are, and that could be very, very triggering.
Haylie Pomroy: It is terrible — especially if you end up on the runway for a long period of time. For me, my response is nausea first, and then mast cell activation second.
Dr. Theoharis Theoharides: Yes, we will talk about that for sure.
Haylie Pomroy: For those of us who feel a clear chemical response — would it be fair to say that there are many people having a negative immunological impact even if they don't have visible reactions the way I do with hives, rashes, and swelling? Is it safe to say that chemical exposure is having a negative impact on everybody?
Dr. Theoharis Theoharides: I dare say that it has an impact on everybody. It's just that some individuals, for reasons we will discuss shortly, are more sensitive, and therefore more likely to have both severe symptoms and chronic sequelae of the problem.
We've known people, for instance, that work in newly renovated offices where a new rug would emanate chemical smells from the glue used to put the carpet down. When cleaning crews come in, they use very strong supplies that linger. There are certain types of lights — especially fluorescent lights — that have a tremendous impact and are likely to cause migraines, headaches, and dysautonomia. People get disoriented.
I remember checking into a five-star hotel in Europe and the moment you walked onto the carpet you could smell whatever they had used. Even I — who don't consider myself to have allergies — was absolutely bothered. I couldn't breathe. So you can imagine other people who are already so sensitive.
And we're still dealing with lead problems in schools in 2025. I mean, give me a break.
Haylie Pomroy: We're seeing clusters of both infection and disease — like glioblastoma — in work environments too, and I love that we're starting to look at the environmental factors that contribute to that.
I want to share something with our community: you may not react the way I do. Maybe you have more functional detoxification pathways, or you don't have methylation problems, or you haven't had a big toxic burden. But if there's something to be filtered, you are the filter. I would love to see products like synthetic air fresheners not be allowed in public settings. All these flowery scents exist because companies believe the consumer wants them — so be vocal. Every hotel I walk into that has scented sheets or carpets, I send an email, leave a note, go to the front desk. Be a positive force for change.
Dr. Theoharis Theoharides: There is an organization out of the Charité Hospital in Berlin that can actually inspect hospitals, hotels, spas, and other facilities upon request to certify them as free of anything associated with multiple chemical sensitivity — no scented soaps, et cetera. That is something we should promote for the United States as well, so that individuals who are sensitive can select places where they're safe.
I had a patient who had an RV outfitted with special filters and would only travel by RV because he was so sensitive. But what really triggered my deep interest in this area is that all the triggers associated with multiple chemical sensitivity are triggers of a unique immune cell called the mast cell — which brings us to mast cell activation disorders.
Haylie Pomroy: I want to say something to our community before we go there. We've been using the word sensitive, and I know for me and for a lot of our community members, that word can sometimes feel like it implies weakness. I'm a physically strong person — I ride 1,400-pound horses. When someone says I'm sensitive to perfume, it can feel like that projects a layer of weakness.
But what I love about the Institute, and especially you, Dr. Theoharides, is that you've helped me understand that I'm having an immunological response. It's not that I can't deal with it — I'm actually having an immunological response. I'm fortunate in that I get visible physical reactions: rashes, lip swelling, blisters. No one can say I'm just picky. But there are so many people whose reactions show up as anxiety, depression, or behavioral changes — like children who walk into scented hotel rooms and seem like a different kid. Hotel sheets alone can contain fungicides, perfumes, and other chemicals.
The word sensitivity makes it seem like you could muscle through it cognitively. I want to reframe that. Please explain what's actually happening in the immune system in individuals like us.
Dr. Theoharis Theoharides: You're absolutely right that there are so many symptoms involving the brain and the nervous system, which complicates things even more. When these immune cells called mast cells — which are found everywhere in the body, including the brain — get activated, they can release chemicals that can affect every organ and tissue of the body. Not necessarily all of them at the same time, but eventually all of them are affected.
Haylie Pomroy: Is it the chemical compounds that trigger the mast cell, or is the mast cell part of the immune system?
Dr. Theoharis Theoharides: Most of the time it is the actual chemicals. Mast cells have been known primarily to react to what is called immunoglobulin E, or IgE — but that's one of about 300 receptors they have on their surface. So they can respond to chemicals, to fungi, to bacteria, to viruses, to stress, to changes in temperature, to changes in vibration. The allergic response is just the tip of the iceberg.
In addition to responding directly to chemicals, the mast cell can respond indirectly as well. When we smell something, the odor is picked up through the olfactory nerve and travels to the part of the brain that regulates homeostasis — the hypothalamus. The hypothalamus releases a hormone called corticotropin-releasing hormone, or CRH. CRH then stimulates the mast cells — it's a second layer of activation — and resets reactivity to practically everything.
Haylie Pomroy: So we smell it, the signal goes up the olfactory nerve, the hypothalamus responds — is that our primal immune response, designed to protect us?
Dr. Theoharis Theoharides: It is. Millions of years ago we didn't have perfumes. Animals smell danger — and that's the important thing. We literally smell danger, and this danger puts us into a fight-or-flight reaction, which triggers the mast cells to orchestrate a response to that danger.
Haylie Pomroy: I just want to punctuate that for everyone. We are smelling danger, and our immune system responds to that danger — and the danger can be a perfume, a fabric softener, jet fuel. Our body responds because it knows it's not good for us.
Dr. Theoharis Theoharides: Absolutely correct. And what is also important — many papers have shown that acute physiological and psychological stress can worsen chemical sensitivities, and that brings us back to exactly what we discussed. A stressful trigger, whether it's physiological — an infection — or psychological, will release CRH, which lowers the reactivity threshold. So while you might have needed 100 units of something to trigger the mast cells, now you need only 10. That's why even small amounts of triggers can cause symptoms — which is central to the definition of multiple chemical sensitivity.
And this is why I like framing this around the mast cell: now we have a concrete physiological response. It's not sensitivity anymore. The mast cells are activated, and they release chemicals that cause all the problems these individuals are describing. This is why, in the United States, there's no diagnostic code for multiple chemical sensitivity — they use other codes, unfortunately including psychosomatic disease, which is pure nonsense. The code we should be using is mast cell activation, unspecified.
Haylie Pomroy: When you mentioned the diagnostic code — who typically diagnoses this? Do you go to an immunologist or an allergist?
Dr. Theoharis Theoharides: The first person you encounter will usually be your general practitioner, pediatrician, or internist. The moment they hear multiple symptoms and sensitivities, they'll probably send you to an allergist. And the allergist invariably doesn't believe this is real — so you're stuck. This is why our institute is so unique, because we're not going to second-guess you. We hear what you have and we try to get to the bottom of it. And since we believe that mast cell activation is involved in virtually every individual who is having these sensitivity symptoms, if we block the mast cells, we will do a lot of good no matter what the triggers might be.
Haylie Pomroy: For those who haven't seen our previous podcasts on mast cells — can you explain what a mast cell is and what mast cell activation means in the body?
Dr. Theoharis Theoharides: Sure. Mast cells are unique immune cells that come from the bone marrow, but they do not circulate as mature cells. They go into the blood and into the tissues, where they take on different characteristics depending on the tissue. They are invariably found around blood vessels and next to nerve endings — uniquely. And they're found in all organs exposed to the outside world: eyes, nose, mouth, lungs, skin, gut. They sense what's happening in the outside world, but they also throw little tentacles between the cells that make up blood vessels — called endothelial cells — and sense what's happening inside the blood as well. They are truly the canary in the mine.
In the brain, mast cells are found specifically around the blood-brain barrier and in the areas that regulate all our body functions — homeostasis — which includes the hypothalamus, hippocampus, and amygdala.
Think of a mast cell as a soccer ball with about a thousand ping-pong balls inside it, each containing about a hundred different chemicals. If you go into an anaphylactic reaction — the worst case — the cell will explode and release the contents of all those granules. Over the following six hours, it will create another hundred or so molecules to be released. This is called the late-phase reaction. Out of the 300 or so molecules that a mast cell releases, we only treat primarily two: histamine and leukotrienes. We have no idea what the others do — including proteolytic enzymes like tryptase and chymase, which I call meat tenderizers. Within 24 hours, the cell restocks itself and is ready to go again. It doesn't die.
Haylie Pomroy: So we typically think of mast cells in terms of leukotrienes and the lung response, and histamine — but there are many other components. And some of those enzymes are active in things like bug bites and bee stings, creating the wheal and itch and redness.
Dr. Theoharis Theoharides: Exactly. And the first thing I do if I suspect someone has these issues is a simple test: I just roll up their sleeve and scratch the underarm in one continuous line. If that scratch turns red within about two minutes, I know there are mast cell and chemical sensitivity issues — because just the pressure of the scratch triggered the mast cells. No allergen. No IgE.
Haylie Pomroy: Just trauma to the tissue. So are there biomarkers or lab tests a person can request if they suspect this? My dad was a chemical engineer who experienced a chemical spill himself and ended up with Bell's palsy as a result. He had a full recovery with detox and antioxidant support, but he was always chemically sensitive afterward. When we were looking at labs, what kind of tests do you run in your clinic?
Dr. Theoharis Theoharides: The quickest approach — though not done in clinic directly — is a skin test with molecules likely to trigger a reaction. This covers both IgE-mediated reactions and direct mast cell activation. For example, to test for reactivity to positively charged molecules, we inject a tiny amount of morphine into the skin — that triggers mast cells without IgE being involved at all. An allergist who is interested can assemble a panel of about 100 different triggers and inject tiny amounts to check for a local reaction. This is confirmatory — individuals usually already know their triggers — but it also opens the door to immunotherapy, where giving tiny amounts repeatedly over time can reduce reactivity. For foods, this can be done sublingually.
Haylie Pomroy: Do you find that once a person has multiple chemical sensitivity, the gut needs to be healed first before they're responsive to those kinds of approaches? A lot of allergists refer patients to me because by the time someone has developed MCS, we need to first heal the gut and reduce systemic inflammation before they'll respond to desensitization.
Dr. Theoharis Theoharides: I agree with you a hundred percent. Desensitization doesn't work for every trigger, and these individuals have so many triggers that it becomes almost a nonsensical approach to try to cover them all. That's why our approach has always been to block the mast cells. Blocking the mast cells is helpful not only in typical allergies and mast cell activation disorders — of which I consider MCS to be one — but it blocks the mast cells from developing further sensitivities, and allows any other approach to work better.
And coming back to your point — since we know the gut-brain axis is very active, and the microbiome plays a significant role, we do have to bring balance to the body first. We look at vitamins, at foods that may be triggering the mast cells, at foods that contain histamine and make things worse in addition to triggering the mast cells. All of those have to be reduced or eliminated first, and then we come in with the second phase of the approach.
Haylie Pomroy: In our community we use the philosophy of remove, restore, and re-inoculate — try to identify and control the triggers, then restore balance and homeostasis, and then rebuild. Every body is different.
I want to circle back to something you said, because it's a reality in my life: when I'm under stress, I am ten times more reactive. My dyslexia is worse. My dysgraphia is worse. My chemical sensitivity is so much worse. Is that because of the inflammatory response in the brain? What's happening there?
Dr. Theoharis Theoharides: As we discussed earlier, the brain will release CRH — and CRH is released not only in the brain, but in the skin, in the gut, in the bladder. We were among the first to show this. It resets the reactivity of the mast cells so they fire more easily and to many more triggers. That's why it's so important to block the mast cells.
And as we've discussed before, some natural molecules can block the mast cells — such as the flavonoid luteolin. The challenge is that luteolin is not absorbed well from the intestine in standard form. That's why I helped formulate it as liposomes mixed with olive oil to increase absorption from the gut. One such product is called PureLute, made by the company Algonot.
Vitamin D3 is also known to be anti-allergic, and about 40% of people are deficient — even those who think they get enough sun. Dietary pro-vitamin D in the skin has to be converted through both the liver and kidneys to become active vitamin D3. For those individuals, I'm a proponent of about 5,000 IU of vitamin D3 per day.
Haylie Pomroy: I carry a little travel kit, and one of the things I take at time of exposure is D3K2. I take beet-derived vitamin C at 3 grams, and I take a larger dose of D3K2 when I'm about to get on a plane or walk through an airport. Even though it's fat-soluble, it has a really strong effect for me — it makes me less reactive. I feel stronger and heartier. So I'm glad you brought that up.
Dr. Theoharis Theoharides: Going back to what can be measured — I always measure total IgE to assess for bona fide allergies. I measure the IgG subclasses IgG1 and IgG4, because IgG4 is responsible for food intolerance and sensitivity through different mast cell receptors. I measure vitamin D3. I measure glutathione, because glutathione is the primary antioxidant our body has, and whenever we're chemically bombarded, we will have oxidative stress. We can give glutathione intranasally, orally, or by injection.
I also measure at least two other molecules that are not exclusive to mast cells, but that I've found strongly correlated with symptom severity: interleukin-6 (IL-6) and vascular endothelial growth factor (VEGF). Both of these can be measured by many standard labs, including Quest and LabCorp.
Haylie Pomroy: I'm so grateful you brought those up. We've been running them at the Institute and on clients from a nutrition perspective, requesting that their doctors order them. The correlation has been really profound. And it gives us the ability to use these biomarkers to track progress — the body will tell us if we're going down the right path.
Dr. Theoharis Theoharides: And certain chemicals can also be measured. Heavy metals, for instance — they stay in the blood for only a couple of months, in urine for about six months, and in hair indefinitely. So if you do a blood test and it's negative, that doesn't mean you were never exposed.
The same is true with mycotoxins. We tend to think mycotoxins come only from mold in water-damaged buildings, but about 50% actually come from food — mold grows on food constantly. Coffee is one notable example. There are laboratories that can measure mycotoxins in the urine. I usually ask for at least two measurements within three months.
I was involved in a case in Massachusetts where, after cannabis was legalized, a number of people became seriously ill and no one could figure out why. It turned out that one particular facility had stored such large quantities that it had gotten molded. When people used the cannabis, they were actually responding to the mold in it, not the cannabis itself. Mold is everywhere.
Haylie Pomroy: We had a case that was identified as Botrytis neurotoxicity — the patient went into a complete psychotic state. It was eventually tracked down through mycotoxin testing. This is the kind of thing we talk about in our clinical applications all the time.
Dr. Theoharides, thank you so much for coming into our community through this podcast and bringing all of this amazing information. Multiple chemical sensitivity is a topic that's near and dear to my heart, affecting so many of our patients with chronic disease, autoimmune disorders, ME/CFS, and myalgic encephalomyelitis. Please promise you'll come back.
Dr. Theoharis Theoharides: Of course. Let me just finish by saying that people exposed to mold or toxins from various pathogens would benefit from a natural molecule called berberine — whether taken prophylactically or after the fact.
And the company I mentioned earlier, Algonot, has another protocol called Brain Gain, which contains five different ingredients that can help when someone is exposed to toxins that may affect the brain — and pretty much every toxin does affect the brain. Just keep in mind that you want to look for products that are as well described and well sourced as possible.
Haylie Pomroy: Thank you so much. This was amazing. People are going to love it, and I hope to see you very soon.
Dr. Theoharis Theoharides: Stay well, Haylie. Talk soon.
If you've ever been told you're "too sensitive" to perfume, cleaning products, or jet fuel — or watched your child fall apart in a scented hotel room and been dismissed as overreacting — this episode is going to change the way you understand what's actually happening in your body.
Haylie Pomroy sits down with Dr. Theoharis Theoharides, Professor of Clinical Immunology, Executive Director of the Center for Excellence in Neuroinflammation Research, and Director of the Institute for Neuro-Immune Medicine-Clearwater, for one of the most clinically rich and personally candid conversations on the show. The topic: multiple chemical sensitivity (MCS), mast cell activation, and the science that finally validates what so many patients have been told is "all in their head."
What Is Multiple Chemical Sensitivity?
Multiple chemical sensitivity — also known as idiopathic environmental illness — is a complex set of symptoms that develop after exposure to even tiny amounts of various environmental substances. The list of triggers is long: benzene, alcohol, formaldehyde (found in wrinkle-resistant cotton clothing), preservatives and dyes in food, perfumes, cleaning products, jet fuel, fluorescent lighting, mycotoxins from mold.
"Because they're such complicated and multiple triggers, and because people have symptoms even to tiny amounts, many colleagues unfortunately don't believe that this is a real problem," Dr. Theoharides explains.
There is currently no diagnostic code for MCS in the United States. Patients who present with multiple symptoms and sensitivities are often sent to allergists, who frequently dismiss the condition as non-real. Without a medical framework to hold it, patients are left without validation, without treatment, and without answers.
Dr. Theoharides's position: the code we should be using is mast cell activation, unspecified — because at the biological root of multiple chemical sensitivity is the mast cell.
The Canary in the Coal Mine
Dr. Theoharides uses a vivid image to describe people with MCS: they are the canary in the coal mine. They react to what everyone is being exposed to — they just react first and more severely.
"I dare say it has an impact on everybody. It's just that some individuals, for reasons we will discuss, are more sensitive, and therefore more likely to have both severe symptoms and chronic sequelae of the problem."
Haylie shares her own story. She was always sensitive to perfumes and dyes as a child — would rash, react, feel sick in traffic. But it wasn't until a heavy malathion exposure in California that her immune system was pushed over the edge, triggering her ITP diagnosis. Looking back, she can now trace the line between chemical exposure, immune response, and the onset of her autoimmune disorder.
This is more common than most people realize. Many individuals with autoimmune conditions can, when they trace backward, link the original onset to a significant environmental exposure. "We usually worry about an immediate reaction, not necessarily the chronic reactions," Dr. Theoharides notes.
What's Actually Happening in the Body
The key to understanding MCS is understanding mast cells.
Mast cells are unique immune cells that originate in the bone marrow and travel to tissues throughout the body — around blood vessels, next to nerve endings, and in every organ exposed to the outside world: the eyes, nose, mouth, lungs, skin, and gut. In the brain, they're found specifically around the blood-brain barrier and in the areas that regulate the body's core functions — the hypothalamus, hippocampus, and amygdala.
Think of a mast cell as a soccer ball filled with roughly a thousand ping-pong balls, each containing a different chemical compound. When triggered, the cell can explode — releasing the contents of all those granules, and then manufacturing another hundred or so molecules over the following six hours. Within 24 hours, it restocks itself and is ready to fire again.
Most medical treatment focuses on just two of the 300-plus molecules mast cells release: histamine and leukotrienes. "We have no idea what the others do," Dr. Theoharides says — including proteolytic enzymes like tryptase and chymase that he calls "meat tenderizers."
Mast cells can be triggered not just by the 300 or so allergens they're classically associated with — they have roughly 300 receptors on their surface and respond to chemicals, fungi, bacteria, viruses, stress, temperature changes, and even vibration. The allergic response most people are familiar with is, as Dr. Theoharides puts it, "the tip of the iceberg."
Why Stress Makes Everything Worse
Here's the piece that brings the science home for so many patients: stress dramatically lowers the threshold for mast cell activation.
When you smell something — even a perfume — that signal travels up the olfactory nerve to the hypothalamus. The hypothalamus releases a hormone called corticotropin-releasing hormone (CRH). CRH, in turn, stimulates the mast cells. So the act of smelling a potential danger resets the reactivity of your entire immune response.
"Millions of years ago, we didn't have perfumes," Dr. Theoharides explains. "We and animals would smell danger — and that's the important thing. We literally smell danger, and this danger puts us into fight-or-flight, which triggers the mast cells to orchestrate a response."
A perfume. A scented laundry detergent. Jet fuel. Your body doesn't know the difference between that and a predator. It responds accordingly.
And stress — physiological or psychological — releases that same CRH, which lowers the bar for how much exposure it takes to trigger a reaction. While you might have needed 100 units of something to set off a response under normal circumstances, under stress you might only need 10. This is why, as Haylie describes, her chemical sensitivity is dramatically worse when she's stressed or depleted — and why stress doesn't "cause" MCS so much as amplify it.
"It's not sensitivity anymore," Dr. Theoharides says. "The mast cells are activated, and they can release chemicals that cause all the problems these individuals are describing."
The Word "Sensitive" Is Misleading
One of the most powerful moments in this conversation is when Haylie pushes back on the language.
"The word sensitive sometimes makes a person feel like you could muscle through it or use your brain cognitively to just suck it up and get through it," she says. "I'm actually having an immunological response. It's not that I can't deal with it."
This reframe matters enormously for patients. MCS is not a personality trait or a character weakness. It is a measurable, physiological immune response. And the fact that not everyone reacts visibly — with hives, blistering lips, or rashes like Haylie — doesn't mean others aren't being affected. Brain fog, anxiety, depression, cognitive difficulties, and behavioral changes in children can all be manifestations of mast cell activation in response to chemical exposure. They're just harder to point to.
Testing: What to Ask For
If you suspect mast cell activation or chemical sensitivity, Dr. Theoharides recommends the following labs:
- Total IgE — to assess for classic allergic reactions
- IgG1 and IgG4 subclasses — IgG4 is responsible for food intolerance and sensitivity through mast cell receptors
- Vitamin D3 — deficiency is common and it has anti-allergic properties; he recommends 5,000 IU daily for most people
- Glutathione — the body's primary antioxidant; chemical bombardment causes oxidative stress and depletes it
- IL-6 (interleukin-6) and VEGF (vascular endothelial growth factor) — both measurable through standard labs like Quest and LabCorp, and strongly correlated with symptom severity
He also notes a simple, no-cost clinical screening: scratch the underside of the forearm in one continuous line. If the scratch turns red within two minutes, mast cell activation is likely. No allergens needed — the mechanical pressure alone triggered the response.
For environmental exposures, Dr. Theoharides also recommends measuring heavy metals (blood for recent exposure, urine for up to six months, hair for long-term) and mycotoxins in the urine — noting that roughly 50% of mycotoxin exposure comes not from moldy buildings but from food.
What Can Help
Avoid the trigger first. Once you know what activates your mast cells, removing or reducing that exposure is the most powerful first step.
Block the mast cells. Rather than trying to desensitize to every possible trigger — an approach that becomes unwieldy when there are hundreds of them — Dr. Theoharides's strategy is to block mast cell activation directly. Some natural compounds that help:
- Luteolin, a flavonoid with demonstrated mast cell-stabilizing properties. Because it isn't well absorbed from the gut in standard form, he recommends liposomal preparations made with olive oil to improve bioavailability.
- Vitamin D3 (approximately 5,000 IU daily) — anti-allergic and widely deficient even in sunny climates, because dietary vitamin D must be converted through both the liver and kidneys to become active
- Berberine — particularly useful for those exposed to mycotoxins or pathogen-derived toxins
- Glutathione — can be administered intranasally, orally, or by injection depending on the clinical situation
Restore gut health and reduce systemic inflammation first. As Haylie notes from her clinical practice, desensitization and other approaches work better once the gut is healed and the inflammatory load is reduced. The gut-brain axis is highly active, and the microbiome plays a significant role in how the immune system responds to triggers.
Track your biomarkers. Using measurable markers — IL-6, VEGF, vitamin D3, glutathione — means you can track whether your interventions are working. The body will tell you if you're heading in the right direction.
Practical Tips for Chemically Sensitive Travelers
Both Haylie and Dr. Theoharides have navigated significant chemical exposure through travel and offer practical guidance:
- Standard 3M masks do not filter odors. You need a mask with activated charcoal to block chemical smells, including jet fuel.
- Jet fuel at airports is a significant trigger for mast cell activation — be proactive before and after flights.
- Hotel sheets, carpets, and cleaning products are common exposure points. Haylie sends emails, leaves notes, and speaks to the front desk about fragrance-free accommodations. Being vocal matters — hotels use scented products because they believe customers want them.
- Take D3K2 at time of exposure — Haylie uses this as a transient immune support strategy when traveling or entering chemically loaded environments.
- Consider a travel supplement kit with beet-derived vitamin C, D3K2, and liposomal luteolin for high-exposure situations.
A Note on Mycotoxins
Dr. Theoharides closes with an important reminder: mold exposure isn't limited to water-damaged buildings. Approximately 50% of mycotoxin exposure comes from food — mold grows on food constantly, and its volatile toxins can trigger mast cell activation, neurological symptoms, and immune dysregulation.
He shared a case from Massachusetts in which a group of people became severely ill from marijuana they'd purchased legally — not from the cannabis itself, but from mold that had contaminated improperly stored inventory. Botrytis neurotoxicity. A complete psychotic break. Eventually tracked down through mycotoxin testing.
If mold exposure is suspected, urine mycotoxin testing from at least two time points within three months is recommended.
About Dr. Theoharis Theoharides
Dr. Theoharis Theoharides is a Professor and Vice Chair of Clinical Immunology and Director at the Institute for Neuro-Immune Medicine-Clearwater, and Adjunct Professor of Immunology at Tufts School of Medicine. He received his BA, MS, MPhil, PhD, and MD degrees from Yale University, where he also received the Winternitz Prize in Pathology. He has 485 publications with over 46,000 citations, an h-index of 106, is rated the worldwide expert on mast cells by Expertscape, and has been inducted into the Rare Diseases Hall of Fame and the World Academy of Sciences.
Connect with Dr. Theoharides:
About Haylie Pomroy
Haylie Pomroy is the Founder and CEO of The Haylie Pomroy Group and a New York Times bestselling author of The Fast Metabolism Diet. With over 25 years of experience in nutrition, biochemistry, and patient advocacy — and her own journey with autoimmune disease and chemical sensitivity — she brings both clinical expertise and lived experience to every conversation.
Learn more and connect with Haylie:
Transcript
Haylie Pomroy: Welcome to Fast Metabolism Matters, where we examine the scientific approach to how your metabolism influences every aspect of your life. I'm Haylie Pomroy, number one New York Times bestselling author. For the past 30 years, I have been creating a support system for vibrant health.
I was in my early 20s battling a life-threatening autoimmune disorder when I learned how vital metabolic health is to our whole being. Join me as I share these insights, and together, let's find out why having a fast metabolism matters.
Today we're going to be talking about multiple chemical sensitivity. Given the conversation that's happening right now about what all these chemicals are doing in our bodies, and what it actually means for the individual, I think this is incredibly important. I am joined by our professor of clinical immunology — the executive director of the Center for Excellence in Neuroinflammation Research. Dr. Theoharis Theoharides, thank you so much for being here with me today.
Dr. Theoharis Theoharides: It was a real pleasure to be with you once more, Haylie.
Haylie Pomroy: Your podcasts have just gone crazy — everybody loves the science that you bring to us in a way that we can apply to real life. Dr. Theoharides trained at Yale School of Medicine, holds a Doctor of Medicine and a Doctor of Philosophy in Pharmacology from Yale University, a Master's of Philosophy in Immunopharmacology and a Master's in Science in Neuroimmunology from Yale, and a Certificate of Global Leadership and Management from the Fletcher School at Tufts University — among many other credentials and honors.
What has been resonating with so many of our community members is your compassion and empathy for what they're going through, and the real-life practical data you give us to change our lives. Let's dive in. I want to talk about multiple chemical sensitivity. How would we define that?
Dr. Theoharis Theoharides: Well, it's almost impossible to define, and it's known by different names, including idiopathic environmental illness. Basically, it's a set of rather complex symptoms that develop after exposure to even tiny amounts of various environmental substances. It could be chemicals like benzene, even alcohol. It could be formaldehyde found sometimes in cotton clothes — added so they don't wrinkle. It could be preservatives and dyes found in foods. The list goes on and on.
And because there are such complicated and multiple triggers, and because people have symptoms even to tiny amounts, many colleagues unfortunately don't believe that this is a real problem.
Haylie Pomroy: When I was diagnosed with my autoimmune disorder, they were doing a lot of tracking back — looking at what had changed in my health. One of the most interesting questions they asked was whether I got carsick in traffic. They said that was sometimes an overlooked symptom in individuals with multiple chemical sensitivity.
I was always sensitive as a kid to perfumes and dyes — I would rash. But it wasn't until I got a heavy malathion exposure that I was pushed over the limit. That was the trigger for my ITP, my autoimmune disorder. After that, I knew what had pushed me over the edge and what to address.
When we talk about multiple chemical sensitivity — are these typically people who are sensitive to cigarette smoke and perfumes, who then go through the world as the canary in the coal mine once their bodies are out of balance?
Dr. Theoharis Theoharides: Well, first of all, you mentioned something very important. Individuals may have symptoms when they're exposed, but many of them also develop autoimmune problems over a period following that first exposure. Looking back, individuals with various autoimmune problems can often link the original symptoms of autoimmunity to such exposures — which is another factor that just doesn't enter into our thinking about what these exposures may do. We usually worry about an immediate reaction, not necessarily the chronic reactions.
I would definitely call them the canary in the mine. I used to travel with a lady who had multiple chemical sensitivity, and every time we went through customs — forced to walk through duty-free — she would absolutely collapse, hit by so many perfumes. There was no way around it. You literally have to wear a chemical mask.
Haylie Pomroy: Duty-free is my nightmare. I literally pack a thick sweatshirt specifically to put over my face and run through. They shouldn't be able to do that.
Dr. Theoharis Theoharides: They shouldn't. And I've written to various countries about airports and no one has ever replied. And before we go on, it's important to say that even the so-called 3M masks that became very prevalent during the pandemic — the ones that can prevent viruses — do not actually clear odors. One has to have a mask with activated charcoal in it, and there are such masks. That would be my advice for anybody who's sensitive to odors, especially jet fuel. Whenever we get to an airport, you smell jet fuel no matter where you are, and that could be very, very triggering.
Haylie Pomroy: It is terrible — especially if you end up on the runway for a long period of time. For me, my response is nausea first, and then mast cell activation second.
Dr. Theoharis Theoharides: Yes, we will talk about that for sure.
Haylie Pomroy: For those of us who feel a clear chemical response — would it be fair to say that there are many people having a negative immunological impact even if they don't have visible reactions the way I do with hives, rashes, and swelling? Is it safe to say that chemical exposure is having a negative impact on everybody?
Dr. Theoharis Theoharides: I dare say that it has an impact on everybody. It's just that some individuals, for reasons we will discuss shortly, are more sensitive, and therefore more likely to have both severe symptoms and chronic sequelae of the problem.
We've known people, for instance, that work in newly renovated offices where a new rug would emanate chemical smells from the glue used to put the carpet down. When cleaning crews come in, they use very strong supplies that linger. There are certain types of lights — especially fluorescent lights — that have a tremendous impact and are likely to cause migraines, headaches, and dysautonomia. People get disoriented.
I remember checking into a five-star hotel in Europe and the moment you walked onto the carpet you could smell whatever they had used. Even I — who don't consider myself to have allergies — was absolutely bothered. I couldn't breathe. So you can imagine other people who are already so sensitive.
And we're still dealing with lead problems in schools in 2025. I mean, give me a break.
Haylie Pomroy: We're seeing clusters of both infection and disease — like glioblastoma — in work environments too, and I love that we're starting to look at the environmental factors that contribute to that.
I want to share something with our community: you may not react the way I do. Maybe you have more functional detoxification pathways, or you don't have methylation problems, or you haven't had a big toxic burden. But if there's something to be filtered, you are the filter. I would love to see products like synthetic air fresheners not be allowed in public settings. All these flowery scents exist because companies believe the consumer wants them — so be vocal. Every hotel I walk into that has scented sheets or carpets, I send an email, leave a note, go to the front desk. Be a positive force for change.
Dr. Theoharis Theoharides: There is an organization out of the Charité Hospital in Berlin that can actually inspect hospitals, hotels, spas, and other facilities upon request to certify them as free of anything associated with multiple chemical sensitivity — no scented soaps, et cetera. That is something we should promote for the United States as well, so that individuals who are sensitive can select places where they're safe.
I had a patient who had an RV outfitted with special filters and would only travel by RV because he was so sensitive. But what really triggered my deep interest in this area is that all the triggers associated with multiple chemical sensitivity are triggers of a unique immune cell called the mast cell — which brings us to mast cell activation disorders.
Haylie Pomroy: I want to say something to our community before we go there. We've been using the word sensitive, and I know for me and for a lot of our community members, that word can sometimes feel like it implies weakness. I'm a physically strong person — I ride 1,400-pound horses. When someone says I'm sensitive to perfume, it can feel like that projects a layer of weakness.
But what I love about the Institute, and especially you, Dr. Theoharides, is that you've helped me understand that I'm having an immunological response. It's not that I can't deal with it — I'm actually having an immunological response. I'm fortunate in that I get visible physical reactions: rashes, lip swelling, blisters. No one can say I'm just picky. But there are so many people whose reactions show up as anxiety, depression, or behavioral changes — like children who walk into scented hotel rooms and seem like a different kid. Hotel sheets alone can contain fungicides, perfumes, and other chemicals.
The word sensitivity makes it seem like you could muscle through it cognitively. I want to reframe that. Please explain what's actually happening in the immune system in individuals like us.
Dr. Theoharis Theoharides: You're absolutely right that there are so many symptoms involving the brain and the nervous system, which complicates things even more. When these immune cells called mast cells — which are found everywhere in the body, including the brain — get activated, they can release chemicals that can affect every organ and tissue of the body. Not necessarily all of them at the same time, but eventually all of them are affected.
Haylie Pomroy: Is it the chemical compounds that trigger the mast cell, or is the mast cell part of the immune system?
Dr. Theoharis Theoharides: Most of the time it is the actual chemicals. Mast cells have been known primarily to react to what is called immunoglobulin E, or IgE — but that's one of about 300 receptors they have on their surface. So they can respond to chemicals, to fungi, to bacteria, to viruses, to stress, to changes in temperature, to changes in vibration. The allergic response is just the tip of the iceberg.
In addition to responding directly to chemicals, the mast cell can respond indirectly as well. When we smell something, the odor is picked up through the olfactory nerve and travels to the part of the brain that regulates homeostasis — the hypothalamus. The hypothalamus releases a hormone called corticotropin-releasing hormone, or CRH. CRH then stimulates the mast cells — it's a second layer of activation — and resets reactivity to practically everything.
Haylie Pomroy: So we smell it, the signal goes up the olfactory nerve, the hypothalamus responds — is that our primal immune response, designed to protect us?
Dr. Theoharis Theoharides: It is. Millions of years ago we didn't have perfumes. Animals smell danger — and that's the important thing. We literally smell danger, and this danger puts us into a fight-or-flight reaction, which triggers the mast cells to orchestrate a response to that danger.
Haylie Pomroy: I just want to punctuate that for everyone. We are smelling danger, and our immune system responds to that danger — and the danger can be a perfume, a fabric softener, jet fuel. Our body responds because it knows it's not good for us.
Dr. Theoharis Theoharides: Absolutely correct. And what is also important — many papers have shown that acute physiological and psychological stress can worsen chemical sensitivities, and that brings us back to exactly what we discussed. A stressful trigger, whether it's physiological — an infection — or psychological, will release CRH, which lowers the reactivity threshold. So while you might have needed 100 units of something to trigger the mast cells, now you need only 10. That's why even small amounts of triggers can cause symptoms — which is central to the definition of multiple chemical sensitivity.
And this is why I like framing this around the mast cell: now we have a concrete physiological response. It's not sensitivity anymore. The mast cells are activated, and they release chemicals that cause all the problems these individuals are describing. This is why, in the United States, there's no diagnostic code for multiple chemical sensitivity — they use other codes, unfortunately including psychosomatic disease, which is pure nonsense. The code we should be using is mast cell activation, unspecified.
Haylie Pomroy: When you mentioned the diagnostic code — who typically diagnoses this? Do you go to an immunologist or an allergist?
Dr. Theoharis Theoharides: The first person you encounter will usually be your general practitioner, pediatrician, or internist. The moment they hear multiple symptoms and sensitivities, they'll probably send you to an allergist. And the allergist invariably doesn't believe this is real — so you're stuck. This is why our institute is so unique, because we're not going to second-guess you. We hear what you have and we try to get to the bottom of it. And since we believe that mast cell activation is involved in virtually every individual who is having these sensitivity symptoms, if we block the mast cells, we will do a lot of good no matter what the triggers might be.
Haylie Pomroy: For those who haven't seen our previous podcasts on mast cells — can you explain what a mast cell is and what mast cell activation means in the body?
Dr. Theoharis Theoharides: Sure. Mast cells are unique immune cells that come from the bone marrow, but they do not circulate as mature cells. They go into the blood and into the tissues, where they take on different characteristics depending on the tissue. They are invariably found around blood vessels and next to nerve endings — uniquely. And they're found in all organs exposed to the outside world: eyes, nose, mouth, lungs, skin, gut. They sense what's happening in the outside world, but they also throw little tentacles between the cells that make up blood vessels — called endothelial cells — and sense what's happening inside the blood as well. They are truly the canary in the mine.
In the brain, mast cells are found specifically around the blood-brain barrier and in the areas that regulate all our body functions — homeostasis — which includes the hypothalamus, hippocampus, and amygdala.
Think of a mast cell as a soccer ball with about a thousand ping-pong balls inside it, each containing about a hundred different chemicals. If you go into an anaphylactic reaction — the worst case — the cell will explode and release the contents of all those granules. Over the following six hours, it will create another hundred or so molecules to be released. This is called the late-phase reaction. Out of the 300 or so molecules that a mast cell releases, we only treat primarily two: histamine and leukotrienes. We have no idea what the others do — including proteolytic enzymes like tryptase and chymase, which I call meat tenderizers. Within 24 hours, the cell restocks itself and is ready to go again. It doesn't die.
Haylie Pomroy: So we typically think of mast cells in terms of leukotrienes and the lung response, and histamine — but there are many other components. And some of those enzymes are active in things like bug bites and bee stings, creating the wheal and itch and redness.
Dr. Theoharis Theoharides: Exactly. And the first thing I do if I suspect someone has these issues is a simple test: I just roll up their sleeve and scratch the underarm in one continuous line. If that scratch turns red within about two minutes, I know there are mast cell and chemical sensitivity issues — because just the pressure of the scratch triggered the mast cells. No allergen. No IgE.
Haylie Pomroy: Just trauma to the tissue. So are there biomarkers or lab tests a person can request if they suspect this? My dad was a chemical engineer who experienced a chemical spill himself and ended up with Bell's palsy as a result. He had a full recovery with detox and antioxidant support, but he was always chemically sensitive afterward. When we were looking at labs, what kind of tests do you run in your clinic?
Dr. Theoharis Theoharides: The quickest approach — though not done in clinic directly — is a skin test with molecules likely to trigger a reaction. This covers both IgE-mediated reactions and direct mast cell activation. For example, to test for reactivity to positively charged molecules, we inject a tiny amount of morphine into the skin — that triggers mast cells without IgE being involved at all. An allergist who is interested can assemble a panel of about 100 different triggers and inject tiny amounts to check for a local reaction. This is confirmatory — individuals usually already know their triggers — but it also opens the door to immunotherapy, where giving tiny amounts repeatedly over time can reduce reactivity. For foods, this can be done sublingually.
Haylie Pomroy: Do you find that once a person has multiple chemical sensitivity, the gut needs to be healed first before they're responsive to those kinds of approaches? A lot of allergists refer patients to me because by the time someone has developed MCS, we need to first heal the gut and reduce systemic inflammation before they'll respond to desensitization.
Dr. Theoharis Theoharides: I agree with you a hundred percent. Desensitization doesn't work for every trigger, and these individuals have so many triggers that it becomes almost a nonsensical approach to try to cover them all. That's why our approach has always been to block the mast cells. Blocking the mast cells is helpful not only in typical allergies and mast cell activation disorders — of which I consider MCS to be one — but it blocks the mast cells from developing further sensitivities, and allows any other approach to work better.
And coming back to your point — since we know the gut-brain axis is very active, and the microbiome plays a significant role, we do have to bring balance to the body first. We look at vitamins, at foods that may be triggering the mast cells, at foods that contain histamine and make things worse in addition to triggering the mast cells. All of those have to be reduced or eliminated first, and then we come in with the second phase of the approach.
Haylie Pomroy: In our community we use the philosophy of remove, restore, and re-inoculate — try to identify and control the triggers, then restore balance and homeostasis, and then rebuild. Every body is different.
I want to circle back to something you said, because it's a reality in my life: when I'm under stress, I am ten times more reactive. My dyslexia is worse. My dysgraphia is worse. My chemical sensitivity is so much worse. Is that because of the inflammatory response in the brain? What's happening there?
Dr. Theoharis Theoharides: As we discussed earlier, the brain will release CRH — and CRH is released not only in the brain, but in the skin, in the gut, in the bladder. We were among the first to show this. It resets the reactivity of the mast cells so they fire more easily and to many more triggers. That's why it's so important to block the mast cells.
And as we've discussed before, some natural molecules can block the mast cells — such as the flavonoid luteolin. The challenge is that luteolin is not absorbed well from the intestine in standard form. That's why I helped formulate it as liposomes mixed with olive oil to increase absorption from the gut. One such product is called PureLute, made by the company Algonot.
Vitamin D3 is also known to be anti-allergic, and about 40% of people are deficient — even those who think they get enough sun. Dietary pro-vitamin D in the skin has to be converted through both the liver and kidneys to become active vitamin D3. For those individuals, I'm a proponent of about 5,000 IU of vitamin D3 per day.
Haylie Pomroy: I carry a little travel kit, and one of the things I take at time of exposure is D3K2. I take beet-derived vitamin C at 3 grams, and I take a larger dose of D3K2 when I'm about to get on a plane or walk through an airport. Even though it's fat-soluble, it has a really strong effect for me — it makes me less reactive. I feel stronger and heartier. So I'm glad you brought that up.
Dr. Theoharis Theoharides: Going back to what can be measured — I always measure total IgE to assess for bona fide allergies. I measure the IgG subclasses IgG1 and IgG4, because IgG4 is responsible for food intolerance and sensitivity through different mast cell receptors. I measure vitamin D3. I measure glutathione, because glutathione is the primary antioxidant our body has, and whenever we're chemically bombarded, we will have oxidative stress. We can give glutathione intranasally, orally, or by injection.
I also measure at least two other molecules that are not exclusive to mast cells, but that I've found strongly correlated with symptom severity: interleukin-6 (IL-6) and vascular endothelial growth factor (VEGF). Both of these can be measured by many standard labs, including Quest and LabCorp.
Haylie Pomroy: I'm so grateful you brought those up. We've been running them at the Institute and on clients from a nutrition perspective, requesting that their doctors order them. The correlation has been really profound. And it gives us the ability to use these biomarkers to track progress — the body will tell us if we're going down the right path.
Dr. Theoharis Theoharides: And certain chemicals can also be measured. Heavy metals, for instance — they stay in the blood for only a couple of months, in urine for about six months, and in hair indefinitely. So if you do a blood test and it's negative, that doesn't mean you were never exposed.
The same is true with mycotoxins. We tend to think mycotoxins come only from mold in water-damaged buildings, but about 50% actually come from food — mold grows on food constantly. Coffee is one notable example. There are laboratories that can measure mycotoxins in the urine. I usually ask for at least two measurements within three months.
I was involved in a case in Massachusetts where, after cannabis was legalized, a number of people became seriously ill and no one could figure out why. It turned out that one particular facility had stored such large quantities that it had gotten molded. When people used the cannabis, they were actually responding to the mold in it, not the cannabis itself. Mold is everywhere.
Haylie Pomroy: We had a case that was identified as Botrytis neurotoxicity — the patient went into a complete psychotic state. It was eventually tracked down through mycotoxin testing. This is the kind of thing we talk about in our clinical applications all the time.
Dr. Theoharides, thank you so much for coming into our community through this podcast and bringing all of this amazing information. Multiple chemical sensitivity is a topic that's near and dear to my heart, affecting so many of our patients with chronic disease, autoimmune disorders, ME/CFS, and myalgic encephalomyelitis. Please promise you'll come back.
Dr. Theoharis Theoharides: Of course. Let me just finish by saying that people exposed to mold or toxins from various pathogens would benefit from a natural molecule called berberine — whether taken prophylactically or after the fact.
And the company I mentioned earlier, Algonot, has another protocol called Brain Gain, which contains five different ingredients that can help when someone is exposed to toxins that may affect the brain — and pretty much every toxin does affect the brain. Just keep in mind that you want to look for products that are as well described and well sourced as possible.
Haylie Pomroy: Thank you so much. This was amazing. People are going to love it, and I hope to see you very soon.
Dr. Theoharis Theoharides: Stay well, Haylie. Talk soon.
