MCAS: Why So Many People Feel Stuck — and Where I Start Instead
What Is MCAS (Mast Cell Activation Syndrome) ?
Mast Cell Activation Syndrome (MCAS) and histamine intolerance have become some of the most talked-about conditions in the functional medicine world. More people are recognizing symptoms like flushing, hives, food sensitivities, anxiety, insomnia, panic, migraines, dizziness, heart palpitations, POTS (postural orthostatic hypertension) digestive issues, and unexplained inflammation—but many are still left wondering what is actually driving these reactions.
Mast Cell Activation Syndrome (MCAS) occurs when mast cells release inflammatory chemicals — including histamine, prostaglandins, leukotrienes, tryptase, cytokines and dozens of other immune mediators — too easily or too often. Instead of responding appropriately to genuine threats like parasites or allergens, mast cells start overreacting to non-threats.
Because mast cells live almost everywhere in the body — the skin, lungs, digestive tract, bladder, blood vessels, brain and connective tissue — symptoms can appear virtually anywhere. This is one reason MCAS is often mistaken for multiple unrelated conditions.
Symptoms:
Hives, flushing or itching
Food sensitivities
IBS, bloating or diarrhea
Migraines
Anxiety or panic attacks
Heart palpitations
Dizziness or POTS symptoms
Brain fog
Chronic fatigue
Sinus congestion
Asthma-like symptoms
Frequent urination
Interstitial cystitis
Hormone-related symptom flares
In fact when multiple systems and barriers are impacted, I often suspect MCAS. This might look like an adult (or child) with eczema/skin rashes, frequent urination AND diarrhea.
What Causes MCAS?
This is probably the biggest question I get and in my practice, I rarely see MCAS develop “out of nowhere”, although it can feel like it did!
A comprehensive in depth intake typically reveals an immune system that has been carrying an excessive burden for years. For children, this “immune load” almost always involves mold or mycotoxin exposure from water damaged buildings. Remember the body doesn’t just decide to stop working.
Common contributors include:
Mold exposure and mycotoxins
Lyme disease and tick-borne infections
Epstein-Barr Virus (EBV)
Bartonella
Chronic viral infections
COVID and spike proteins- we can test for this!
Environmental toxins
Gut infections
Parasites
Candida overgrowth
Hormonal fluctuations
Nutrient deficiencies
Chronic psychological stress
Trauma
Sleep deprivation
None of these automatically causes MCAS. Rather, they continually signal danger to the immune system until mast cells become increasingly reactive and lose their normal threshold for activation.
Chronic Infections and MCAS
Many chronic infections are capable of activating mast cells directly. Covid, Lyme disease, Bartonella, Babesia, chronic viral infections like Epstein Bar Virus (EBV), mold-related illness, intestinal infections, and even persistent dysbiosis all stimulate inflammatory cytokines that keep the immune system on high alert.
Consequently, these infections can lead to chronic immune activation and with this chronic immune activation, the system continues to behave as though there is an unresolved threat and mast cells continue to break open releasing their contents, leading to a bucketful of miserable and confusing symptoms.
Why Mold and MCAS Are So Closely Connected
Mold is one of the first things I think about when I see someone with significant mast cell activation. Very often, when we go far enough back through the history, there has been a significant mold or water-damaged building exposure somewhere along the way. It may not have been the moment all of the symptoms started, and the person may not have made the connection at the time, but it can be an important triggering event that begins to change how the immune system responds and set up susceptibility later on.
What makes mold particularly challenging is that it doesn't necessarily affect just one system. Exposure can create immune signaling across the respiratory tract, gut, skin and nervous system at the same time. These are also some of our most important barrier and immune-surveillance systems. When that signaling continues, we can begin to see increasing sensitization and immune dysregulation across multiple areas of the body. The person who once tolerated most foods, supplements, smells and environments may suddenly find that their threshold for everything seems to be getting smaller.
This is where the MCAS picture can become much more obvious. There may be new food reactions, histamine intolerance, flushing, itching, rashes, headaches or migraines, dizziness, brain fog, heart-rate changes, sleep disruption, temperature sensitivity, chemical or fragrance sensitivity, and reactions to supplements that were previously well tolerated. Sometimes there aren't many classic “allergy” symptoms at all. The nervous system may be where the mast cell activity is showing up most strongly, with migraines, sensory sensitivity, agitation, insomnia, nerve pain or dysautonomia-type symptoms.
Mold can also become part of a much larger immune picture. When the immune system has been under this kind of pressure, I often start looking at what else has been allowed to take hold or become harder for the body to manage—gut dysbiosis, fungal overgrowth, chronic or previously encountered infections, impaired barrier function and ongoing inflammatory signaling. At that point, treating every reaction individually can become an endless game of whack-a-mole.
This is why I don't look at MCAS as simply a histamine problem. Mast cell stabilizers, antihistamines, a low-histamine diet and supportive nutrients can certainly have a place, but I also want to know why the mast cells became so reactive in the first place. Mold isn't the only possible contributor, and the science doesn't support saying that it causes every case of MCAS, but clinically it is an exposure I don't want to overlook. When the history points us there, understanding what happened in the environment—and whether there is still an exposure keeping the system activated—can be an important part of putting the bigger picture together.
Many molds also produce mycotoxins capable of triggering significant immune activation. These toxins increase oxidative stress, damage epithelial barriers like the gut and sinuses, activate inflammatory pathways and can directly stimulate mast cells.
For some people, even walking into a water-damaged building for a few minutes can trigger headaches, flushing, anxiety, congestion, brain fog or gastrointestinal symptoms and depending on where this person is in their cycle, their daily stress load, even what day of the week it is can affect whether it happens one day and not the next. This is where I come in. To help you to draw the connections and put together the pieces so that you can heal.
The Nervous System and MCAS
One thing that isn’t discussed enough is the conversation happening between mast cells and the nervous system.
Mast cells constantly communicate with nerve endings and with microglia, the immune cells of the brain.
When mast cells become activated, they release inflammatory chemicals that can affect mood, concentration, motivation, sleep, pain perception and emotional regulation.
Likewise, when the nervous system perceives ongoing danger, it sends signals back to mast cells, encouraging further activation.
This creates a frustrating cycle where immune dysfunction fuels nervous system dysregulation, and nervous system dysregulation continues fueling immune dysfunction.
It’s one reason so many people describe feeling like they’re “not themselves. Individuals who may have once described themselves as “easy-going” and generally happy are finding themselves deeply depressed, lacking motivation and feeling like they can’t remember who they used to be.
Another interesting piece is that mast cells and nerves can activate each other. Mast-cell mediators can sensitize nearby nerve endings, while neuropeptides released from activated nerves can further stimulate mast cells. That can create a feedback loop of mast-cell activation → nerve irritation → more mast-cell signaling, particularly around sensory and trigeminal pathways.
This is also why someone can have significant mast-cell-related neurological symptoms without dramatic hives, swelling, or classic allergy symptoms. The dominant presentation may be migraine, brain fog, dysautonomia, sensory sensitivity, insomnia, nerve pain, or episodic anxiety/adrenaline sensations rather than skin symptoms.
Symptoms can include:
Brain fog, slowed processing, trouble finding words
Difficulty concentrating or feeling mentally “offline”
Headaches or migraines, including pressure-type headaches
Facial, sinus, jaw or trigeminal-type pain/pressure
Light or sound sensitivity
Dizziness, disequilibrium or feeling floaty
Tinnitus or ear pressure
Tingling, burning, crawling or electric sensations
Increased nerve sensitivity or neuropathic-type pain
Internal vibration or tremulousness
Muscle twitching
Restlessness or feeling neurologically “wired”
Sudden anxiety, agitation or a sense of adrenaline without an obvious psychological trigger
Irritability or emotional lability
Insomnia, especially feeling exhausted but unable to settle
Palpitations, heart-rate swings or orthostatic symptoms
Temperature dysregulation, flushing or chills
Nausea or motion sensitivity
Profound fatigue or a “crash” after a flare
Cognitive or neurological symptoms that fluctuate dramatically from hour to hour or day to day
Why Do MCAS Symptoms Flare During Hormonal Changes?
If you’ve ever noticed your symptoms worsen around ovulation, before your period or during perimenopause, you’re definitely not imagining it.
Estrogen naturally stimulates mast cells to release more histamine, while histamine can also increase estrogen activity.
This creates a feedback loop where rising estrogen can make histamine symptoms worse, and elevated histamine can further disrupt hormonal balance.
Many women notice increased migraines, anxiety, insomnia, flushing, itching or digestive symptoms during these higher-estrogen phases of their cycle.
Understanding your own hormonal rhythm can be incredibly helpful as oftentimes supports can be put into place to help shift these hormonal fluctuations and set you up for success around your cycle. Knowing when you are most susceptible is key! Do we need more supports during the beginning of your cycle, around ovulation or towards the end. Can we love on your liver a little more around various points in your cycle or do we need to shift the way you eat to help decrease immune reactivity and promote estrogen clearance and detoxification?
Can MCAS Be Reversed?
Healing can happen when enough of the underlying immune burden is reduced that mast cells no longer need to remain on constant alert.
That often means improving sleep, stabilizing blood sugar, restoring digestion, addressing nutrient deficiencies, calming the nervous system, treating chronic infections, removing mold exposure, and gradually helping the immune system to rebuild tolerance.
Ultimately, our goal is to raise the threshold at which the immune system reacts in the first place.
Mast cells are incredibly intelligent immune cells doing exactly what they believe they need to do to protect you and my job is to find out why they’ve remained on high alert for so long.
When we slow down enough to understand the full picture—the immune burden, the nervous system, the infections, the hormones, the gut, the environment—that’s when we can finally stop chasing symptoms and start creating lasting healing.
Why My Approach to MCAS Is Different
Our goal is not to simply suppress mast cells although this can be a game changer for some and many of my clients come to me on more than a few mast cell supports. They’re often taking Quercetin, Luteolin, DAO Enzymes, antihistamines, Ketotifen, Cromolyn Sodium—sometimes all at once. They’re following an extremely restrictive low-histamine diet and avoiding more and more foods and their world of what they feel they can tolerate continues to get smaller.
But our work doesn’t stop here. When someone develops Mast Cell Activation Syndrome, I want to understand why their immune system has become so reactive in the first place.
Is mold keeping the immune system activated?
Is Lyme disease, Bartonella, Babesia, Epstein-Barr virus, or another chronic infection continually stimulating mast cells?
Is gut inflammation preventing histamine from being broken down effectively?
Are hormone fluctuations increasing mast cell degranulations and histamine release?
Is poor sleep, blood sugar instability, chronic stress and nervous system dysregulation keeping the body in a constant state of perceived danger?
One of my primary goals is to help your immune system to rebuild immune tolerance. A healthy immune system doesn’t react to every food, smell, chemical, or environmental exposure. It knows the difference between what is dangerous and what isn’t. When that tolerance has been lost, mast cells often begin responding to harmless things as though they are threats. Over time, by reducing the immune burden and improving regulation, we can teach the immune system that it no longer has to stay on high alert. This is where healing happens!
Just a few of my favorite supports: Available via Fullscript for a 10% discount.
GI Hist - Neurobiologix: This formula supports more than gut histamine by helping regulate immune and inflammatory pathways throughout the body. By calming reactivity and supporting antioxidant and detox processes, it helps to improve digestive symptoms, immune balance, and systemic symptoms linked to histamine and inflammation..
Transfer Immune Factors - Researched Nutritionals: Transfer Immune Factors are a go-to for immune dysregulation and MCAS, especially in cases involving long-COVID and chronic EBV. Rather than suppressing symptoms, they help retrain immune communication, calm overactive inflammatory signaling, and improve immune tolerance — making them especially helpful for sensitive, reactive nervous and immune systems.
Phosphatidylcholine - Body Bio: a foundational cell-membrane and nervous-system stabilizer. It helps repair and protect cell membranes, calm inflammatory signaling, and support healthy immune tolerance. In MCAS and post-infectious states, mast cells and immune cells often have “leaky,” unstable membranes — PC helps quiet reactivity at the cellular level.
Important! Educational only. This content is not medical advice. Always work with a qualified healthcare provider before changing medications, supplements, or treatment plans.