Mast Cell Activation Syndrome

Mast cells are immune sentinels stationed throughout the body, concentrated in areas exposed to the external environment: skin, airways, gut lining, and blood vessels. When functioning normally, they release targeted bursts of histamine and other mediators to fight pathogens and coordinate healing. In Mast Cell Activation Syndrome (MCAS), these cells become hypersensitive and degranulate excessively in response to triggers that would not normally provoke a reaction. The result is a wide range of symptoms that can seem unrelated: flushing, hives, rapid heart rate, GI distress, headaches, brain fog, and sensitivity to foods, chemicals, or temperature changes.

SARS-CoV-2 appears to activate mast cells through multiple pathways. The spike protein can directly trigger mast cell degranulation. Persistent viral fragments may sustain this activation long after the acute infection resolves. Elevated inflammatory cytokines further prime mast cells to overreact. This creates a feedback loop: activated mast cells release more histamine and inflammatory mediators, which increase tissue inflammation, which further sensitizes mast cells. Many Long COVID patients who develop new food sensitivities, chemical intolerances, or unexplained allergic reactions after their infection are experiencing this cycle.

Management of MCAS in Long COVID focuses on stabilizing mast cells and reducing the histamine burden. Quercetin is a natural flavonoid with mast cell stabilizing properties that may help reduce degranulation. N-acetylcysteine (NAC) supports glutathione production, which may help modulate oxidative triggers of mast cell activation. Low-histamine dietary modifications can reduce the total histamine load on the body. Dr. Groysman screens for MCAS patterns in his Long COVID patients, particularly those who report new onset sensitivities, because addressing mast cell activation early may help prevent the cascade from becoming entrenched.