Mast Cell Activation Syndrome (MCAS)

What Is Mast Cell Activation Syndrome (MCAS)?

Mast Cell Activation Syndrome (MCAS) is a complex condition in which mast cells — a type of immune cell — release chemicals too easily, causing widespread inflammation and allergic-like symptoms throughout the body.

Mast cells normally help defend the body against allergens and infections by releasing chemicals like histamine. In MCAS, these cells become overactive and release excessive amounts of these chemicals without an appropriate trigger. This can affect many organs and systems, including the skin, digestive tract, cardiovascular system, and nervous system.

Common Signs & Symptoms

• Flushing, hives, or itching

• Nasal congestion or wheezing

• Rapid heartbeat (tachycardia) or low blood pressure

• Lightheadedness or fainting

• Fatigue and brain fog

• Nausea, bloating, or diarrhea

• Difficulty regulating body temperature

• Poor sleep quality

MCAS often overlaps with Ehlers-Danlos Syndromes (EDS) and Postural Orthostatic Tachycardia Syndrome (POTS), and may also mimic other conditions like allergies, autoimmune disorders, long COVID, or ME/CFS.

Treatment in Mast Cell Activation Syndrome (MCAS)

• Identify and avoid triggers

• Antihistamines (under doctor care)

• Low-histamine diet

• Stress management

Connection to Other Multisystem Disorders

Many people with Mast Cell Activation Syndrome also have conditions like Ehlers-Danlos Syndrome (EDS) or POTS.