What is MCAS?

“My body is constantly having an allergic reaction.”

This is my quick response when people ask what is mast cell activation syndrome (MCAS). In truth, this disease much more complicated than typical allergies.

My mast cells are overactive; they release chemicals, such as histamine, when they aren’t supposed to. These chemicals cause a variety of symptoms such as fatigue, hives, migraine, IBS, bone pain, muscle weakness, vomiting, tachycardia, dizziness, PMDD, and anxiety. Symptoms can range in severity from discomfort to disability. Mast cell reactions can can cause life-threatening complications, including anaphylaxis.

Certain foods and activities can make MCAS worse. For me, these triggers include exercise, fragrances, high histamine foods, hot or cold temperatures, hormone fluctuations, and stress. Everyone is different.

MCAS has been linked to Postural Orthostatic Tachycardia Syndrome (POTS) and Ehlers-Danlos Syndrome (EDS). 

Tests can help diagnose MCAS. However, no test, including tryptase, can rule out MCAS and false negatives are common. MCAS blood tests include:

  • Serum tryptase
  • Serum chromogranin A
  • Plasma histamine chilled on ice
  • Plasma PGD2 chilled on ice
  • Plasma PGF2a chilled on ice
  • Plasma heparin chilled on ice

PGD2, PGF2a, leukotriene E4, and n-methylhistamine are best measured by a 24-hour chilled urine test, but you must keep the container cold AT ALL TIMES. Random urines may also be helpful, but the specimen should be kept on ice and frozen immediately. Testing availability varies greatly and is ever-changing.

Each MCAS patient tolerates medication and supplements differently, but the goal is to reduce and block as many mast cell mediators (chemicals released by mast cells) as possible. Please talk to your doctor before adding any medications or supplements, and research all of the ingredients, as inactive ingredients can be triggers for MCAS. Here are a few examples:

  • Cetirizine blocks H1 histamine receptors
  • Famotidine blocks H2 histamine receptors
  • Montelukast sodium inhibits leukotrienes
  • Aspirin inhibits prostaglandins
  • Cromolyn sodium stabilizes mast cells
  • Ketotifen stabilizes mast cells
  • Vitamin C inhibits histamine production
  • Vitamin D stabilizes mast cells
  • Quercetin stabilizes mast cells
  • Tumeric decreases prostaglandins

For more information, check out the following resources:

For a longer read, I highly recommend Never Bet Against Occam: Mast Cell Activation Disease and the Modern Epidemics of Chronic Illness and Medical Complexity by Lawrence B. Afrin. Although many MCAS patients have mild symptoms, this book illustrates the complexity of MCAS.