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Mast Cell Activation Syndrome (MCAS): A Common but not well known cause of allergies, eczema, faints, headaches, anaphylactic reactions, rashes, swelling, feeling inflamed, joint pains, anxiety, IBS

Updated: Jul 3

Are you struggling with menopausal symptoms despite being on HRT? Have allergies, eczema, hay fever, prone to anaphylactic reactions, fainting spells or IBS, fluid retention and weight gain, bloating, anxiety, poor sleep, joint pains, headaches, dry eyes, sinus problems?

Do you know a younger person struggling with similar symptoms? This blog is for you.

If you’ve had your hormones balanced but still have symptoms, you may have MCAS. MCAS symptoms include headaches, tiredness, brain fog, fluid retention, gut problems, joint problems, allergies, eczema, asthma, sinus problems, urticaria, and poor sleep.

Understanding Mast Cell Activation Syndrome (MCAS)

Mast Cell Activation Syndrome (MCAS) is a condition characterized by the overactivity of mast cells, which release excessive amounts of chemicals like histamine, tryptase, prostaglandins, and leukotrienes. These chemicals can cause a range of symptoms across various systems in the body. Here’s a look at the symptoms, diagnosis, treatment, prevalence, causes, and prognosis of MCAS.

Symptoms of MCAS

MCAS symptoms vary widely and can fluctuate. Common symptoms include:

- Skin: Hives, flushing, itching, swelling, and skin reactions.

- Digestive System: Stomach pain, nausea, vomiting, diarrhea, bloating, and acid reflux.

- Heart and Blood Vessels: Low blood pressure, rapid heart rate, dizziness, and fainting.

- Lungs: Wheezing, shortness of breath, and nasal congestion.

- Brain and Nerves: Headaches, brain fog, fatigue, and sleep problems.

- Muscles and Joints: Muscle pain, joint pain, and weakness.

- Mental Health: Anxiety, depression, and mood swings.

- Other: Severe allergic-like reactions (anaphylaxis) without clear triggers, symptoms worsened by stress or exercise. MCAS and POTS, Ehlers Danlos can co exist.

Diagnosis of MCAS

Diagnosing MCAS involves multiple steps:

1. Medical History: A thorough review of symptoms and potential triggers.

2. Lab Tests:

- Serum Tryptase: Elevated levels of tryptase in the blood.

- 24-Hour Urine Test: Checking for N-methylhistamine, prostaglandin D2, and leukotriene E4.

- Other Chemicals: Elevated levels of histamine, chromogranin A, and heparin.

3. Biopsies: In some cases, skin or gut tissue samples to check for increased mast cells.

4. Response to Treatment: Symptom improvement with mast cell-targeted therapies.

Management and Treatment of MCAS

The Global Consensus-2 guidelines provide a detailed management strategy for MCAS, including:

1. Avoiding Triggers: Identifying and avoiding known triggers, such as specific foods, medications, and environmental factors, is crucial.

2. Medications:

- Antihistamines:

  • H1 Blockers: Medications like cetirizine, loratadine, and fexofenadine . Higher doses may be more effective (e.g., cetirizine up to 10 mg twice a day, fexofenadine up to 180 mg three times a day).

  • H2 Blockers: Ranitidine and famotidine for additional histamine control.

  • Mast Cell Stabilizers: Cromolyn sodium and ketotifen to prevent mast cell degranulation.

  • Leukotriene Inhibitors: Montelukast ) and zafirlukast to manage symptoms related to leukotrienes.

  • Prostaglandin Inhibitors: Low-dose aspirin to reduce prostaglandin D2 levels, used cautiously.

  • Corticosteroids: Prednisone for short-term severe symptom control.

  • Other Medications: Omalizumab for allergic symptoms, benzodiazepines for anxiety.

3. Dietary Modifications: A low-histamine diet, avoiding foods that trigger symptoms.

4. Supplements: Vitamin C and quercetin for their antihistamine properties.

5. Managing Comorbidities: Treating associated conditions like Ehlers-Danlos syndrome (EDS) and Postural Orthostatic Tachycardia Syndrome (POTS).

6. Regular Monitoring: Continuous monitoring by healthcare providers to adjust treatment plans based on symptom changes.

7. Supportive Care: Psychological support and physical therapy to enhance quality of life.

Diamine oxidase (DAO),

DAO an enzyme involved in the breakdown of histamine and other biogenic amines in the body.L helps metabolize histamine ingested from foods or produced by the body, which is particularly relevant for individuals with histamine intolerance or mast cell disorders.

In individuals with reduced DAO activity or deficiency, histamine levels can build up in the body, leading to symptoms such as headaches, digestive issues, skin problems, and more, similar to those experienced in mast cell disorders.

Some research suggests that supporting DAO activity through diet or supplements may help manage symptoms associated with histamine intolerance or mast cell disorders.

Foods that are rich in DAO cofactors, such as vitamin B6, copper, and vitamin C, may help support DAO activity.

Examples include:

Foods high in vitamin B6: Chicken, turkey, salmon, tuna, chickpeas, potatoes, bananas, and sunflower seeds.

Foods high in copper: Shellfish, organ meats (like liver), nuts, seeds, and cocoa.

Foods high in vitamin C: Citrus fruits, strawberries, kiwi, bell peppers, broccoli, and Brussels sprouts.

A list of supplements that can help:

Supplements can play a supportive role in managing Mast Cell Activation Syndrome (MCAS), but it's crucial to discuss their use with a healthcare provider before starting, as individual needs and responses can vary. The top 3 easy to access supplements are: DAO supplements , taken just before meal. High dose slow release vitamin C is particularly useful. Magnesium and vitamin D and K2 can also help.

Here is a more comprehensive list of supplements that may be helpful for some individuals with MCAS:

1. DAO supplements: DAO (Diamine Oxidase) supplements are typically used to help manage symptoms associated with histamine intolerance. Histamine intolerance occurs when there is an imbalance between the amount of histamine in the body and the ability to break it down. DAO is an enzyme that helps break down histamine in the gut, and taking DAO supplements can support this process.

Purpose: DAO supplements are intended to aid the breakdown of histamine, which can help reduce symptoms of histamine intolerance, such as headaches, digestive issues, skin problems, and respiratory symptoms.

How to Use: DAO supplements are usually taken before meals, as they work by breaking down the histamine in food. Follow the dosage instructions on the supplement packaging or as advised by a healthcare professional.

Effectiveness: The effectiveness of DAO supplements can vary from person to person. Some people with histamine intolerance may experience significant relief from symptoms, while others may notice less improvement.

Dietary Considerations: In addition to taking DAO supplements, managing histamine intolerance often involves dietary adjustments. This includes avoiding high-histamine foods such as aged cheeses, processed meats, fermented products, alcohol, and certain vegetables and fruits.

2. Quercetin: Quercetin is a flavonoid with anti-inflammatory and antioxidant properties. It may help stabilize mast cells and reduce histamine release. However, its effectiveness can vary among individuals.

3. Vitamin C: Vitamin C is an antioxidant that can help reduce inflammation and support immune function. It may also have antihistamine properties and support the activity of enzymes like DAO.

4. Vitamin B6: Vitamin B6 is involved in the synthesis of neurotransmitters and may help support the activity of DAO, the enzyme involved in histamine metabolism.

5. Omega-3 fatty acids: Omega-3 fatty acids, found in fish oil supplements, may help reduce inflammation and support immune function. They may be beneficial for individuals with inflammatory conditions like MCAS.

6. Probiotics: Probiotics can help support gut health by promoting the growth of beneficial bacteria. A healthy gut microbiome may help regulate immune function and reduce inflammation, which could be beneficial for individuals with MCAS.

7. Digestive enzymes: Digestive enzymes may help support digestion and nutrient absorption, which can be important for individuals with MCAS who may experience gastrointestinal symptoms.

8. Quinolinic Acid (QA): Some individuals with MCAS have been found to have elevated levels of QA, which may contribute to symptoms. Supplements that target QA metabolism, such as niacin or magnesium, may be considered in these cases.

9. Butyrate: Butyrate is a short-chain fatty acid that may help support gut health and reduce inflammation. It can be found in supplements or produced by certain gut bacteria from dietary fiber.

10. Adaptogens: Adaptogenic herbs like ashwagandha, rhodiola, and holy basil may help support the body's response to stress, which can be a trigger for mast cell activation in some individuals.

Prevalence and Causes of MCAS

Prevalence: MCAS is relatively new to medicine, with prevalence estimates suggesting it might affect up to 17% of the population to some extent, though severe cases are less common.

Causes (Aetiology): The exact cause of MCAS is not fully understood but likely involves:

- Genetics: Genetic mutations affecting mast cell function.

- Environment: Allergens, infections, stress, and certain foods as triggers.

- Immune System Issues: Dysregulation leading to inappropriate mast cell activation.

- Related Conditions: Often seen with other disorders like EDS and POTS.

Prognosis of MCAS

The prognosis for MCAS varies:

- Mild to Moderate Cases: Many patients improve significantly with the right treatment and lifestyle changes.

- Severe Cases: Some patients have persistent, severe symptoms despite treatment but can achieve stable periods.

- Chronic Condition: MCAS typically requires ongoing management, with symptoms potentially changing over time.


MCAS is a complex condition involving the overactivity of mast cells, leading to a wide range of symptoms. Effective management involves a personalized approach, including avoiding triggers, medications, dietary modifications, and supportive care. With proper treatment and monitoring, many patients can achieve significant symptom relief and improved quality of life.

For more detailed information, resources, and support, consider visiting reliable websites such as

- [The Mastocytosis Society](

For information on histamine-free diet, you can visit: Choose compatible with histamine intolerance and change filters to give you a list of what you can eat or a list of what you can’t eat.




1. Afrin, L. B., Ackerley, M. B., Bluestein, L. S., & Brewer, J. H. (2016). Mast Cell Activation Syndrome (MCAS): A Disorder Distinct from Mastocytosis. Immunology and Allergy Clinics of North America, 36(2), 233–252.

2. Molderings, G. J., Haenisch, B., Brettner, S., Homann, J., Menzen, M., Dumoulin, F. L., Panse, J., Butterfield, J., Afrin, L. B., & Sotlar, K. (2016). Pharmacological Treatment Options for Mast Cell Activation Disease. Naunyn-Schmiedeberg's Archives of Pharmacology, 389(7), 671–694.

3. Valent, P., Akin, C., Bonadonna, P., Hartmann, K., Brockow, K., Niedoszytko, M., Nedoszytko, B., Siebenhaar, F., Sperr, W. R., Elberink, J. N. G. O., & Butterfield, J. H. (2012). Standards and Standardization in Mastocytosis: Consensus Statements on Diagnostics, Treatment Recommendations and Response Criteria. European Journal of Clinical Investigation, 42(10), 1063–1073.

4. The Mastocytosis Society. (n.d.). Retrieved from

These references provide valuable information and support for individuals seeking further understanding and resources on Mast Cell Activation Syndrome.

Images courtesy of Google

By Dr Purity Carr

GP&Menopause Doctor



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