MCAS(Mast Cell Activation Syndrome)

Alex Oh • 11 July 2026

Have you heard of MCAS or suffer from it?  It seems to be a growing diagnosis, especially for perimenopausal women.


Mast Cell Activation Syndrome (MCAS) causes episodic, multi-system symptoms due to overactive mast cells releasing chemical mediators like histamine, affecting the skin, gut, respiratory system, cardiovascular system, and more.


Common Symptoms:

MCAS symptoms are highly variable and can affect multiple organs simultaneously, often fluctuating in severity and frequency. Common manifestations include:

  • Skin and mucous membranes: Flushing, hives (urticaria), itching, swelling, and angioedema (rapid swelling of skin, lips, or airways) which can be life-threatening in severe cases (anaphylaxis) 
  • Gastrointestinal: Nausea, vomiting, diarrhea, abdominal cramping, bloating, and food intolerances 
  • Cardiovascular: Rapid heartbeat (tachycardia), low blood pressure, dizziness, fainting, and lightheadedness 
  • Respiratory: Shortness of breath, wheezing, nasal congestion, and throat tightness 
  • Neurological and cognitive: Brain fog, headaches, fatigue, difficulty concentrating, and mood changes 
  • Musculoskeletal: Joint pain, muscle aches, and generalized weakness


Triggers and Episodic Nature

Symptoms often come and go, sometimes triggered by infections, medications, foods, insect stings, stress, or environmental factors. The severity can range from mild discomfort to life-threatening anaphylaxis, and the same individual may experience different symptoms at different times 

Severe Reactions

In rare cases, MCAS can cause anaphylaxis, characterized by rapid swelling of the skin and airways, severe drop in blood pressure, and difficulty breathing. Immediate medical attention is required in such situations


Diagnosis Considerations

Because MCAS symptoms overlap with many other conditions, diagnosis typically requires lab tests during or shortly after an episode (e.g., serum tryptase, urine histamine or prostaglandins) and a positive response to medications targeting mast cell mediators, such as antihistamines or leukotriene receptor antagonists 

Fluctuations in Estradiol and Progesterone can drive up histamine through mast cell degranulation and downregulate DAO (which helps break down histamine).

Progesterone stabilizes mast cells and upregulates DAO production.

Histamine is not just an immune mediator but functions as a major neurotransmitter.  For example,histamine acts as wake promoting neurotransmitter which can drive hyperarousal and insomnia.  Therefore, thorough testing of hormones would be recommended.



Practical Advice

Keeping a symptom diary can help track triggers and patterns, aiding healthcare providers in diagnosis and management. Identifying and avoiding triggers, along with appropriate pharmacological/herbal treatment, can help reduce the frequency and severity of symptoms 


MCAS is a complex, multi-system disorder with unpredictable symptoms, making individualized care and careful monitoring essential for effective management.