Mast Cell Activation Syndrome (MCAS)
Evaluation and Care for Mast Cell Activation Syndrome
What is Mast Cell Activation Syndrome?
Mast cell activation syndrome (MCAS) is a condition in which mast cells — a type of immune cell — release excessive chemical mediators, causing recurrent episodes of severe allergic-type reactions (anaphylaxis) that affect two or more body systems at the same time.
Mast cells normally play a role in immune defense and allergic responses. In MCAS, activation occurs unpredictably and can produce symptoms across multiple organ systems. MCAS is diagnosed only after other conditions that could explain the symptoms have been ruled out.
What are common symptoms of MCAS?
MCAS symptoms occur in episodes and typically involve two or more of the following organ systems at the same time:
- Skin: Flushing, hives, itching, or swelling
- Gastrointestinal: Abdominal pain, cramping, nausea, vomiting, or diarrhea
- Cardiovascular: Rapid heart rate, lightheadedness, fainting, or low blood pressure
- Respiratory: Shortness of breath, wheezing, or throat swelling
Some patients also report headaches, difficulty concentrating, or brain fog, though these are not part of the core diagnostic criteria.
Symptoms come and go in episodes and can sometimes be mistaken for anxiety or other unexplained conditions. A key feature of MCAS is that symptoms are episodic and recurrent — not constant.
Is MCAS related to Ehlers-Danlos Syndrome?
Some patients with Ehlers-Danlos Syndrome (EDS) and hypermobility disorders report symptoms that overlap with mast cell activation. A growing number of clinical reports describe co-occurrence of:
- Connective tissue disorders (such as EDS)
- Dysautonomia (such as postural orthostatic tachycardia syndrome, or POTS)
- Mast cell activation
When symptoms of these conditions overlap, an integrated evaluation — rather than isolated symptom treatment — can help ensure accurate diagnosis and appropriate care.
How is MCAS diagnosed?
Diagnosis requires meeting all three of the following criteria:
1. Recurrent episodes of severe allergic-type symptoms affecting two or more organ systems at the same time
2. Laboratory-confirmed elevation of mast cell mediators (most commonly serum tryptase, measured within 1–4 hours of a symptomatic episode, showing a rise of at least 20% plus 2 ng/mL above your personal baseline)
3. Improvement of symptoms with medications that block mast cell mediators
Because MCAS symptoms can mimic many other conditions, your physician will also work to rule out other possible causes. Evaluation by a physician experienced with complex multisystem disorders and mast cell conditions is important.
How is MCAS treated?
Treatment is individualized based on which organ systems are affected and how severe the symptoms are. Management often includes:
- Trigger identification and avoidance (including specific foods, medications, or environmental exposures that provoke episodes)
- H1 antihistamines (such as cetirizine or loratadine) and H2 antihistamines (such as famotidine)
- Leukotriene receptor antagonists (such as montelukast)
- Mast cell stabilizers (such as cromolyn sodium or ketotifen)
- Aspirin (for flushing or blood pressure drops, when appropriate)
- Omalizumab or corticosteroids for symptoms that do not respond to other treatments
- An epinephrine autoinjector (EpiPen) — all patients with a history of severe systemic reactions should carry one at all times
Coordinated care with allergy/immunology is recommended.
When should you seek evaluation for MCAS?
Consider evaluation if you experience:
- Recurrent episodes of unexplained allergic-type reactions affecting multiple body systems
- Fainting, flushing, hives, and gastrointestinal symptoms occurring together without a clear cause
- Unusual sensitivities to medications
- Overlap with EDS or dysautonomia symptoms
Because MCAS can be difficult to recognize, a comprehensive evaluation helps reduce misdiagnosis and improve symptom management.
Why integrated care matters in MCAS
MCAS rarely exists in isolation. Patients may experience overlapping connective tissue, autonomic, or gastrointestinal symptoms. A whole-person approach to care ensures that treatment plans consider the full medical picture — not just isolated reactions — and that each condition is diagnosed using validated criteria before treatment is started.
