MCAS: understanding symptoms, triggers and when to seek help

Flushing, digestive upset and a racing heart can feel like unrelated problems. When symptoms recur together, it is worth discussing the pattern with a doctor. Mast cell activation syndrome (MCAS) is one possible explanation, but these symptoms can also have other causes.

This article draws on allergy guidance and patient education resources to help you understand MCAS and prepare for a useful medical conversation.

What is MCAS?

Mast cells are immune cells found throughout the body, including the skin, digestive tract and airways. They release chemical messengers, known as mediators, which help the body respond to threats. Histamine is one of these messengers.

In MCAS, inappropriate or excessive mast cell activation can produce symptoms in several body systems. Symptoms may fluctuate and look different from one person to another. [Mast Cell Action](https://www.mastcellaction.org/about-mcas)

Looking at the whole symptom history can help a clinician understand how different complaints may relate to one another. Symptoms and individual triggers provide a starting point for discussion, rather than a checklist for self-diagnosis.

What symptoms can occur?


Typical episodes can involve:

- **Skin:** flushing, itching, hives or swelling.

- **Gut:** abdominal cramps, nausea, vomiting or diarrhoea.

- **Breathing:** wheezing or breathlessness.

- **Circulation:** a racing pulse, low blood pressure or faintness.

These symptoms warrant assessment, particularly when several occur together. [AAAAI: MCAS](https://www.aaaai.org/conditions-treatments/related-conditions/mcas)

People living with mast cell disorders also report fatigue, headache and brain fog. These are non-specific symptoms: they do not, by themselves, establish MCAS. [The Mast Cell Disease Society: patient perspectives](https://www.mastcellaction.org/assets/_/2021/09/13/d413ffbd-2d8d-4ab0-be1c-ee240788bd77/mcas-patients-perspective.pdf?v=1)

## What can trigger a flare?

Potential triggers include temperature changes, alcohol, certain foods or medicines, infections, exercise, stress and fragrances. A trigger for one person may be well tolerated by another. [Mast Cell Action](https://www.mastcellaction.org/about-mcas)

The aim is to identify reproducible patterns, not to assume that every food or everyday exposure is harmful. A symptom diary can help record what happened, when it started, possible exposures and any treatment taken. Photographs of visible skin changes may also help your clinician understand an episode. [Mast Cell Action resources](https://www.mastcellaction.org/resources)

## How is MCAS assessed?

Symptoms alone are not enough. Widely used consensus criteria look for three elements: recurrent systemic episodes affecting more than one body system; a measurable rise in mast cell mediators during an episode; and improvement with appropriate treatment.

Assessment may include blood tryptase measured during a reaction and compared with a baseline sample, and selected urine tests. Timing matters. An allergy or immunology specialist can advise on testing and investigate alternative explanations. Improvement after an antihistamine alone does not confirm MCAS. At the CWC we find testing for mould, mycotoxins, the gut microbiome and stool PCR analysis can alps help. [AAAAI diagnostic guidance](https://www.aaaai.org/conditions-treatments/related-conditions/mcas)

## What can help?

Care is individual. Depending on the assessment, a clinician may recommend antihistamines or other medicines that target mast cell mediators. Treatment should be reviewed for benefit and side effects. [AAAAI treatment information](https://www.aaaai.org/conditions-treatments/related-conditions/mcas)

Practical adjustments can also help make daily life more manageable. Introduce changes gradually and seek professional support, especially if food reactions are leading to a restricted diet. A long list of exclusions is not a substitute for an assessment or an individual nutrition plan. [Mast Cell Action self-management toolkit](https://www.mastcellaction.org/assets/_/2023/06/26/6fb5eecf-26e1-40a8-a724-0ea2d7310952/mcas-self-management-toolkit.pdf?v=1)

## When to seek urgent help

**Sudden throat or tongue swelling, severe breathing difficulty or collapse can indicate anaphylaxis. Use your prescribed adrenaline auto-injector immediately if available and call 999. Do not wait for a rash.** Follow your emergency plan; do not stand or walk. If symptoms have not improved after five minutes, use a second auto-injector if available. [NHS anaphylaxis guidance](https://www.nhs.uk/conditions/anaphylaxis/)

## A thoughtful first step in Cardiff

You do not need to arrive at an appointment with a diagnosis. Bring your symptom history, current medicines and supplements, previous results and the questions that matter to you.

Cardiff Wellness Centre offers GP-led consultations with a detailed medical and lifestyle history. If recurring symptoms are affecting your wellbeing, [book a consultation](https://cardiffwellnesscentre.janeapp.co.uk/) to discuss your concerns and appropriate next steps. Specialist assessment may be needed.

The centre also offers the following tests, where clinically appropriate:

- **Mould blood test — £230.**

- **PCR stool test for toxins — £210.**

Your clinician can explain what each test measures, its limitations and whether it is appropriate for your symptoms. These tests do not establish an MCAS diagnosis.

*Educational information, not an individual diagnosis or treatment plan. [Dr Tania Dempsey](https://drtaniadempsey.com/mast-cell-activation-syndrome/) is acknowledged as an educational source; this article does not imply her endorsement of Cardiff Wellness Centre.*