Mast Cell Activation Syndrome Main Info Page

What Is Mast Cell Activation Syndrome?

Mast Cell Activation Syndrome (MCAS) features inappropriate mast cell activation, causing not only typical symptoms of allergy but also a host of other symptoms across multiple organ systems. MCAS drives chronic multi-system inflammation and allergy and affects the skin, gastrointestinal, cardiovascular, respiratory, and neurologic systems; it is often a component of pain syndromes.

Most patients present with decades of chronic multisystem comorbid symptoms that are either inflammatory and or allergic in nature.

A mast cell is a type of white blood cell known as a mastocyte that contains a lot of histamine and heparin and thus plays a large role in allergies and anaphylactic reactions. This key player in the immune system is also involved with pathogenic defense, wound healing, inflammation and blood-brain-barrier function.

Histamine is a neurotransmitter that is released by cells as part of an allergic response or as a response to injury. A histamine release typically causes symptoms such as:

• Rashes
• Itching
• Swelling
• Stuffy nose

However, in MCAS these and other symptoms (see below) can often be chronic and more severe in nature.

Symptoms of Mast Cell Activation

Mast cells do not just release histamine; instead, they release their contents (which includes chemicals such as cytokines, chemokines and growth factors) into surrounding tissues, causing symptoms when chronically activated such as:

• Loose stools
• Joint pains
• Runny nose after meals
• Headaches
• Brain fog
• Palpitations
• Blood sugar instability
• Painful urination
• Increased urinary frequency
• Irritability
• Concentration problems
• Memory loss
• Neuropsychiatric issues
• Fatigue

Common Mast Cell Triggers

Mast-cell activation can look like a histamine intolerance, but with a mast cell activation, there are many more triggers for activation than happens with a histamine intolerance. Potential triggers of mast cell activation are:

• Fungi
• Sunlight
• Histamine-containing foods
• Alcohol
• Some medications
• Parasites
• EMFs
• Metals
• Pesticides
• BPA and other toxins
• Hormones

MCAS symptoms may flare during common allergy months in both the spring and fall. Researchers have discovered that allergic, environmental and emotional stress can result in brain mast cell activation, which can lead to a focal disruption of the blood-brain barrier, neuroinflammation and seizures.

In addition, once the blood-brain barrier is breached, pathogenic infections can cross into the brain and lead to conditions such as Lyme disease, PANS, PANDAS, autoimmune encephalitis as well as potentially to neurodevelopmental conditions such as autism, ADHD and Sensory Processing Disorder.

The takeaway from this is that if your child has allergies, eczema, asthma, an autoimmune disorder or other type of chronic inflammation, they may be vulnerable to an onset of these disorders due to Mast Cell Activation Syndrome.

Link to Toxicant and Synthetic Exposures in MCAS

Exposure to toxicants and synthetic chemicals is increasingly recognized as a root cause and perpetuating factor in MCAS. Pesticides, heavy metals, mold toxins (mycotoxins), plastics like BPA, flame retardants, and other environmental chemicals can directly activate mast cells and impair the body’s ability to regulate immune responses.

Dr. Claudia Miller, a physician and researcher at the University of Texas, developed a framework called TILT — Toxicant-Induced Loss of Tolerance — which offers an important lens for understanding why some people develop MCAS. Dr. Miller’s theory proposes that an initial exposure to a sufficient load of chemicals (from sources such as pesticides, contaminated water, indoor air pollution, or a moldy building) can cause a breakdown in the body’s tolerance, after which even small, everyday exposures to chemicals, foods, or other substances begin to trigger symptoms.

This is part of the “total load” model that Documenting Hope teaches. This loss of tolerance closely mirrors what is seen in MCAS, where the threshold for mast cell activation becomes increasingly low and the range of triggers increasingly broad. Reducing the total toxic burden through cleaner food, water, air, and personal care products is an important part of addressing the underlying drivers of MCAS rather than simply managing its symptoms.

Link to Infections

Because mast cells play a key role in the defense system against pathogens, people with chronic infections such as Lyme disease, Bartonella, fungal infections, herpetic viral infections, PANS and PANDAS may develop MCAS. In many of these cases, these infections are undiagnosed and untreated, thus leading to chronic mast cell activation.

The Role of the Nervous System in MCAS

The nervous system and the immune system are in constant communication, and in MCAS, this relationship can become a significant driver of symptoms. The autonomic nervous system (the branch responsible for regulating automatic functions like heart rate, digestion, and stress response) directly influences mast cell behavior. When the body perceives a threat, whether physical or emotional, the nervous system triggers a stress response that can activate mast cells and cause them to release histamine and other inflammatory mediators.

This is why emotional stress appears on the list of MCAS triggers: it isn’t just psychological, it has a measurable biological impact. Many people with MCAS are stuck in a chronic state of nervous system dysregulation, sometimes called “fight-or-flight,” in which the body is perpetually primed for threat. This keeps mast cells on high alert, lowers the threshold for activation, and makes it harder for the body to resolve inflammation. Addressing nervous system dysregulation is therefore not a secondary concern in MCAS. It is a root-cause issue that must be part of any comprehensive healing approach.

Mast Cell Activation Syndrome Healing Checklist

Strategies for Regulating the Nervous System in MCAS

Because nervous system dysregulation can perpetuate the cycle of mast cell activation, calming and retraining the nervous system is an important part of recovery. Practices that activate the parasympathetic nervous system (the “rest and digest” state) can help lower the baseline level of immune activation over time.

Deep, diaphragmatic breathing is one of the simplest and most accessible tools: slow, extended exhales signal safety to the brain and can reduce mast cell reactivity in the moment. Many people advocate for the 4-7-8 breathing method. This is a technique that involves inhaling for 4 seconds, holding the breath for 7 seconds, and exhaling for 8 seconds.

Vagus nerve stimulation, whether through humming, gargling, cold water on the face, or dedicated devices (VNS devices), is another approach gaining attention for its ability to dampen inflammatory responses.

Somatic therapies, such as EMDR, Somatic Experiencing, or the Gupta Programme, are specifically designed to help the nervous system unlearn chronic threat responses, an important step for those whose MCAS is intertwined with trauma or prolonged stress.

Gentle movement practices like yoga or qigong, along with prioritizing deep and consistent sleep, also support nervous system recovery. Neurological chiropractic, gentle osteopathic manipulation or cranial sacral therapy are effective ways to help retrain the nervous system back into a state of safety.

Smoothing out blood sugar spikes and dips can reduce stress on the body, which can help to control inflammation that exacerbates MCAS. Be sure to emphasize fat, fiber and protein in your child’s diet while limiting or eliminating processed foods and sugar.

Check for Mold

Mold, mycotoxins and biotoxins are known and common triggers of MCAS. Your home or child’s school may have a mold issue, and you may not be aware of it. A common tipoff is if symptoms improve when the child is not a home or at school. Learn how to identify mold and water damage in your home here. We also recommend watching our interview of PJ Harlow here and our interview of Cory Levy about The Dust Test here. You can get a 15% discount off of the Dust Test with code HOPE15.

Trial a Low-Histamine Diet

To do this, avoiding certain high-histamine foods such as:

• Processed, cured or smoked meats
• Soy sauce and tamari
• Vinegar
• Beer
• Wine
• Other foods
• Leftover foods

Once histamine is created in leftovers, it cannot be destroyed. Although a low-histamine diet can help many, others may need to refine their diet by also incorporating:

• Gluten-free/dairy-free diet
• Ketogenic diet (see below)

Consider a Ketogenic Diet

Tania Dempsey MD noted that many of her patients tend to do better on a ketogenic diet rather than a low-histamine diet. Because a ketogenic diet removes all sugar and refined carbohydrates from the diet, it can do an excellent job at stabilizing blood sugar, cortisol and inflammation.

Detoxify Your Environment and Support the Gut and the Liver

A body cannot heal if it is in a chronic state of stress trying to deal with an onslaught of toxic exposures. This means cleaning up your home and work environments and removing as many synthetics as possible. This includes fragrances, detergents, personal care products that contain chemicals and removing any processed foods that contain chemicals.

Once you’ve cleaned your external environment, it is important to clean and support your internal environment. Detoxification requires a healthy liver and gut. A properly functioning liver is necessary for the breakdown of histamine; therefore, a poorly functioning liver may lead to a longer occurrence of histamine-related symptoms. Learn more about detoxification here.

Healing the gut and improving liver function will help your body eliminate any new or stored toxins but it will also help with reducing histamine and inflammatory responses. In addition, a healed gut is one that is not chronically constipated and thus allows toxins processed by the liver to be quickly eliminated from the body.

Integrate Supportive Supplementation

Your healthcare practitioner may recommend any of the following supplements to help with symptoms:

• Homeopathic histamine
• Hesperidin
• Ellagic acid
• Pomegranate

Be sure to consult a healthcare practitioner to see if any of these supplements are the right fit for you or your child.

Still Looking for Answers?

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