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.

Tools for You

• Validated Mast Cell Activation Syndrome Questionnaire (Questionnaire)

• Mast Cell Activation Syndrome Questionnaire (Questionnaire)

• 7 Root Causes of MCAS (Link to eds.clinic Website)

Helpful Video links on what is MCAS?

• What is MCAS Playlist (YouTube)

• Basics of POTS and MCAD self-care - Leslie Russek PT (61 min Video)

Identify and Avoid Triggers

Because mast cells in MCAS patients are hyper-reactive, they can "explode" or degranulate in response to a wide array of stimuli that do not affect the general population.

• Common Triggers: These include temperature changes (hot showers or cold air), emotional stress, physical trauma, and environmental factors like fragrances, mold, or certain chemicals.

• Physical Irritants: Mechanical pressure from tight clothing or adhesives (like medical tape) can also trigger a localized or systemic reaction.

• Journaling: Patients are encouraged to keep a symptom journal to track what they eat and what they are exposed to, which can help identify specific, individualized patterns.

Antihistamines (Under Doctor Care)

Treatment often begins with blocking the effects of histamine, one of the primary inflammatory chemicals released by mast cells.

• H1 Blockers: These are traditional allergy medications such as cetirizine (Zyrtec), loratadine (Claritin), or fexofenadine (Allegra).

• H2 Blockers: These medications, such as famotidine (Pepcid), are typically used to reduce stomach acid but are vital in MCAS for blocking histamine receptors found in the gut and other tissues.

• Dosing Protocols: For MCAS, doctors often recommend a "cocktail" of both H1 and H2 blockers, sometimes at higher-than-standard doses (e.g., twice daily) to effectively manage symptoms.

Low-Histamine Diet

While not all patients respond to dietary changes, many find that reducing the "histamine bucket" in their body helps stabilize their system.

• Foods to Limit: Patients should avoid aged and fermented foods (like aged cheeses, wine, and sauerkraut), leftovers (which develop histamine over time), and high-histamine produce such as spinach, tomatoes, and eggplant.

• Elimination Strategy: It is often recommended to follow a strict low-histamine diet for about three weeks before slowly reintroducing foods one by one to monitor for adverse reactions.

Stress Management

Psychological and emotional stress are well-documented direct triggers for mast cell degranulation.

• The Stress-Flare Connection: Stress signals the brain to activate the sympathetic nervous system, which can cause mast cells to release inflammatory mediators throughout the body.

• Calming Modalities: Techniques such as meditation, yoga, diaphragmatic breathing and vagal nerve techniques are suggested to help calm the nervous system and bring the body back into a state of balance (homeostasis).

• Neurological Impact: Managing stress is particularly important because mast cell mediators can cross the blood-brain barrier, contributing to "leaky brain" and symptoms like brain fog and anxiety

Tools for You

• Swedish list of histamine foods referenced in Mast Cells in the Gut (Handout)

Helpful Video links on MCAS Treatment?

• MCAS Treatment Playlist (YouTube)

• Basics of POTS and MCAD self-care - Leslie Russek PT (61 min Video)

• OT Emily:Oh The pOTsabilities - Emily Rich OT (YouTube channel)

• DINET - Dysautonomia Information Network (Website)

• Dysautonomia International on YouTube (YouTube)

• Dysautonomia International (Website)

• Dysautonomia - The EDS Clinic Learning Center (Website)

• MCAS - The EDS Clinic Learning Center (Website)

• Leslie Russeks "Hypermobility 101" (Website)

• Bendy Bodies Podcast - Linda Bluestein MD (Website)

• Elevation Wellness - Patricia Stott PT (YouTube channel)

• Dr Claire - Claire Francomano MD (YouTube channel)

• Movement & Exercise (M&BPC Website)

• Mindfulness Activities (M&BPC Website)