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Mast Cell Activation Syndrome (MCAS)

MCAS is also commonly referred to as Mast Cell Activation Disorder (MCAD)

Let’s start with “what’s a mast cell?”

Mast Cells
Human Mast Cells (looking like blueberries.)

Unless you’re a medical professional you’ve probably never heard of them. I certainly hadn’t. Mast cells are best known for being a key player in serious allergic reactions… like someone having anaphylaxis from bee stings or peanuts, or an asthma attack triggered by something like smoke.

These cells are part of the immune system and play a vital role in chemical transmission throughout the body, though the details are still poorly understood. These little cells are activated and actually explode (fancier term- degranulate) to release a huge variety of chemicals, presumably depending on what activated them. These chemicals are used to mediate other reactions like digestion and many other things yet to be discovered; this is why you’ll often hear these released chemicals referred to as mediators. One thing they do seem to know- mast cells promote inflammation and cell proliferation for wound healing.

Mast cells are born from stem cells in the bone barrow. They’re prolific, being found in most tissues throughout the body, but the greatest numbers are found in the gastrointestinal tract and skin. They’re even found in close contact with neurons, but the exact purpose is still a mystery under research.

What is MCAS?

This is what happens when mast cells aren’t working properly. For some reason (not yet known) these cells are releasing chemicals when they shouldn’t, resulting in a list of unpleasant symptoms. It’s speculated that maybe mast cells are altered genetically, maybe as a part of a connective tissue problem, or perhaps that MCAS is even autoimmune in nature. The fact is we don’t know yet, but researchers are working on it. Also important to know is that MCAS is NOT the same as mastocytosis. MCAS is essentially having a normal amount of mast cells that aren’t working correctly, whereas mastocytosis is a problem of too many mast cells thanks to a cell proliferating out of control (akin to cancer).

Watch mast cells degranulate…


I can’t do this justice, but these are common symptoms I often hear about in addition to my own. Yes, there is a lot of overlap with POTS symptoms. For a very thorough description Page 50 of: Presentation, Diagnosis, and Management of Mast Cell Activation Syndrome by Dr. Lawrence Afrin.

Mental: Anxiety, Brain fog- difficulty concentrating & recalling words/facts/memories, Depression, Mood swings, Panic attacks, Irritability

Gastrointestinal: Abdominal Pain, Constipation, Cramping, Diarrhea, Nausea

Dermatological: Chronically dry skin, Flushing, Foliculitis, Hives, Itching, Pale skin, Rashes, Dermatographia (skin writing- raised warm red welts from scratches)

Respiratory: Chronic congestion, Coughing, Nasal stuffiness, Wheezing, Difficulty breathing deeply

Cardiovascular: Heart palpitations, Dizziness, Fainting, Near-fainting, Lightheadedness, Low blood pressure, High blood pressure

Vision: Blurred vision, Dry irritated eyes, Red eyes

Auditory: Sound sensitivity, Tinnitus

Pain: Headaches, Migraines, Joint pain, Chest pain, (Abdominal pain)

Other: Weight gain and retention despite low calorie intake and exercise, Slow time to heal wounds

Anaphylaxis If too many mediators are spilt into your system, you may also experience anaphylaxis, which primarily includes: difficulty breathing, itchy hives, flushing or pale skin, feeling of warmth, weak and rapid pulse, nausea, vomiting, diarrhea, dizziness and fainting.

Anecdotally, those who react immediately after exposure to a trigger are called “shockers,” and those that react later are called “leakers.”

Common triggers

These common triggers are things that can cause symptoms, or just make those symptoms so much worse.

  • Specific foods (specific to patient)
  • Emotional and physical stress
  • Exercise
  • Hot or cold temperatures
  • NSAIDS (non-steroidal anti-inflammatory drugs), antibiotics, and other medications
  • Skin friction or pressure
  • Strong scents or smells (even from innocent perfumes)
  • Bug bites

A fantastic review of MCAS and how to test for it, by Dr. Andrew White of Scripps:

More References:

Mast Cell Activation Syndrome- A Review:

Mast cell activation disease: a concise practical guide for diagnostic workup and therapeutic options:

Presentation, Diagnosis, and Management of Mast Cell Activation Syndrome by Dr. Lawrence Afrin:

Mayo Clinic- Anaphylaxis:


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