In this article, you will learn:

  • What are mast cells
  • What are mast cell disorders, including mast cell activation syndrome (MCAS)
  • Symptoms of MCAS
  • Common Root Causes
  • How to Get a Diagnosis for MCAS
  • How to Treat MCAS
  • How to Get Support and Raise Awareness


What are mast cells?

Mast cells are a type of white blood cell that regulate the immune system. They play an important role in how the immune system responds to an infection. Mast cells are produced by bone marrow and are released in an immature form into the blood until they reach the tissues, where they mature. They are found throughout the body and are located between the boundaries of tissues and the external environment e.g.  skin around the blood vessels and the lining of the gut. They are found in most tissues, in particular locations of the body that are close to the environment like the skin and the intestines so that they can detect pathogens immediately upon entering the body.

Mast cells store a number of different chemical mediators, including histamine, tryptase and chymase. These mediators are released selectively when there is a mast cell or allergic reaction.

What are mast cells infographic


What are mast cell disorders?

In healthy people, mast cells operate to effectively protect the body against infections from pathogens. For someone who has mast cell disease, these cells behave badly, inappropriately activating in response to a variety of triggers such scents, temperature changes, foods, exercise, among others. Mast cell disorders can be primary (mastocytosis), secondary (reactive) or idiopathic.

The primary mast cell disorder, mastocytosis, occurs when there is an abnormal accumulation of mast cells in one or more organ systems. It is a rare condition, impacting fewer than 200,000 people in the US alone. Secondary mast cell disorders are the most common and include allergic reactions, anaphylaxis, urticaria, among others.

Once primary and secondary mast disorders are ruled out, your medical practitioner will make a final assessment as to whether there is enough evidence to diagnose an idiopathic mast cell disorder, which arise spontaneously and for which the cause is unknown. Mast cell activation syndrome falls within this category. There is no consensus around the definition or diagnosis for MCAS, which is why your doctor may be unfamiliar with the condition or question whether it exists.

MCAS is a type of mast cell disease in which the mast cells are inappropriately triggered and “degranulate”, releasing mast cell mediators into the body. Mast cells carry over 200 chemical mediators but the ones most commonly detected in the blood with MCAS are:

  • Histamine
  • Serine proteases such as tryptase and chymase
  • Serotonin

Symptoms of MCAS

Symptoms of MCAS can be broadly categorized into the following areas:

  1. Skin related symptoms: itching, hives (urticaria), flushing, swelling
  2. Gastrointestinal symptoms: diarrhea, nausea, abdominal cramps, bloating
  3. Heart related symptoms: low blood pressure, weak or rapid pulse, dizziness
  4. Lung related symptoms: wheezing, shortness of breath, throat swelling, coughing

It’s important to note that you may only experience some of these symptoms, the severity of which can change quickly. Each case is individual and two people with MCAS may have very different symptoms.  

Common triggers for MCAS

Some potential mast cell triggers include:

  • Strong scents, perfumes, natural odors
  • Stress
  • Environmental changes: air pressure, sudden temperature changes, changes in levels of pollution or pollen etc.
  • Exercise
  • Alcohol
  • Certain foods or beverages, particularly those that are high in histamine such as cheese and shellfish
  • Drugs (NSAIDs, opioids, antibiotics)
  • Sunlight
  • Fatigue
  • Insect bites
  • Exposure to mold, Lyme disease or co-infections
  • Infections (bacterial, viral or fungal)
  • Heavy metal toxicity
  • Medications that liberate or block DAO (diamine oxidase, the enzyme that breaks down histamine)

Common root causes

The root cause for MCAS will vary by individual. Some of the more common root causes are listed below:

  1. Poor gut health – IBD, SIBO
  2. Infections
  3. Toxicity (including heavy metal toxicity)
  4. Genetic factors

There is very little literature on the root causes of MCAS because there is still much to be discovered about this condition. As awareness is raised and doctors gain more familiarity with MCAS, we will slowly start to gather more data around the condition and gain additional clarity on the root causes.


How to Get a Diagnosis

One paper proposes practitioners ask the following questions when diagnosing MCAS:

  1. Are there symptoms indicating the release of mast cell mediators impacting 2 or more organ systems (e.g. skin, respiratory, gastrointestinal, cardiovascular)?
  2. Following an episode, is there a “transient” increase in a mast cell mediator (a common test, is to check the levels of the mast cell mediator serum tryptase up to 4 hours after the onset of symptoms)
  3. Do these symptoms respond to specific treatments that effect mast cell mediators (e.g. H1 antihistamines)?

Other doctors may take a similar approach to a diagnosis, doing a thorough background check on historical symptoms and testing for other mast cell mediators in the blood. For more information, please see our post on how to get a HIT or MCAS diagnosis.


How to Treat MCAS

Because of the range of symptoms and the fact that each individual case is unique, treatment for MCAS is highly individualized and requires a trial and error approach. Generally speaking, the following treatments have been commonly prescribed:

  1. Avoiding triggers – it is critical that a patient understand his / her triggers and work to avoid them as much as possible
  2. Medications – treatment will typically start with antihistamines and can move on to other products. Generally speaking, a positive response to medications can be seen within 1-2 months. Patients will move through multiple medications until a personalized medical protocol can be determined
  3. Natural medications – natural supplements such as Quercetin (natural antihistamine), Vitamin C and Magnesium can be used but it’s important to keep in mind that not all patients will respond the supplements
  4. Symptomatic treatment – for example gastric complaints may be treated directly with proton-pump inhibitors and interstitial cystitis may be treated with amphetamines and so on
  5. Diet – staying away from foods that cause a reaction (not all high histamine foods will cause a reaction, it’s important to note which ones you’re sensitive to) and incorporate foods that naturally raise your DAO levels such as saturated fats and foods that are high in iron, vitamin B12, among others

It is important to remember that the above options may not be treating the root cause of a patient’s MCAS, which must be addressed in order to achieve long-term results.

How to Get Support and Raise Awareness

To get support on MCAS and raise awareness on the condition, join our community forum, learn about the importance of communities in the healing process, and actively seek a medical practitioner who understand the condition.


Akin, C., Valent, P. and Metcalfe, D. (2010). Mast cell activation syndrome: Proposed diagnostic criteria. Journal of Allergy and Clinical Immunology, 126(6), pp.1099-1104.e4.

Cookson, H., Clive G. (2016). An Update on Mast Cell Disorders. Clin Med (Lond), 16(6): 580–583.

Molderings, G. J. et al. (2011) ‘Mast cell activation disease: a concise practical guide for diagnostic workup and therapeutic options’, Journal of Hematology & Oncology, 4(1), p. 10. doi: 10.1186/1756-8722-4-10.

Molderings, G.J., Haenisch, B., Brettner, S. et al. Naunyn-Schmiedeberg’s Arch Pharmacol (2016) ‘Pharmacological treatment options for mast cell activation disease’, 389: 671.

Urb, M. and Sheppard, D. (2012). The Role of Mast Cells in the Defence against Pathogens. PLoS Pathogens, 8(4), p.e1002619.