Mast Cell Activation Syndrome (MCAS) is a condition in which mast cells, a type of white blood cell involved in the immune system, become overactive and release excessive amounts of chemical mediators such as histamine. This inappropriate release causes a wide range of symptoms affecting multiple body systems, often mimicking severe allergic reactions or anaphylaxis

. Mast cells normally help defend the body by releasing chemicals in response to allergens or infections. In MCAS, however, these cells react excessively and sometimes without a clear trigger, leading to symptoms such as swelling, hives, itching, flushing, diarrhea, vomiting, difficulty breathing, low blood pressure, and neurological issues like brain fog and headaches

. Symptoms typically involve two or more body systems, including the skin, cardiovascular system, gastrointestinal tract, respiratory system, and nervous system. The severity of episodes can vary, with some cases resulting in life- threatening anaphylaxis

. The exact cause of MCAS is not fully understood, but it may be linked to genetic factors such as mutations in the KIT gene. Triggers can include stress, temperature changes, certain foods, or environmental chemicals, though sometimes no specific trigger is identifiable

. In summary, MCAS is a disorder of mast cells causing them to release excessive chemicals, leading to recurrent and severe allergic-type symptoms across multiple organ systems, often without a clear cause