Welcome

Whether you or a loved one has recently been diagnosed with Mast Cell Activation Syndrome (MCAS), or you’re just starting to learn about this complex condition, we want you to know you’re not alone. Understanding MCAS can feel overwhelming at first, with its wide range of symptoms, triggers, and treatments, it’s normal to have many questions and uncertainties.

This page is designed to be your first step towards clarity and confidence, offering reliable, easy-to-understand information and practical guidance.

At Mast Cell Action, we’re committed to providing compassionate support and empowering you with knowledge so you can navigate your journey with hope and strength. Take your time exploring this page, and remember - we’re here for you every step of the way.

What is Mast Cell Activation Syndrome (MCAS)?

MCAS is a condition that can develop in both children and adults. It sits within a spectrum of mast cell disorders and may occur alongside conditions like mastocytosis or hereditary alpha tryptasemia syndrome (HATS). In MCAS, mast cells release chemicals (mediators) too often or in response to things that aren’t usually harmful, such as certain foods, fragrances, or changes in temperature. This can cause a wide range of symptoms affecting different parts of the body.

Triggers and symptoms vary widely between individuals and can change over time, making the condition difficult to manage. In some cases, symptoms become more frequent or severe as the condition progresses. The causes of MCAS aren’t fully understood, but genetics may play a role. For example, HATS is linked to extra copies of the alpha tryptase gene and can be identified with genetic testing. Find out more here.

Diagnosing MCAS

Getting an MCAS diagnosis can take time, as symptoms vary and overlap with other conditions. Many doctors are still unfamiliar with the condition, and testing can be inconsistent. Diagnosis is usually based on:

• Multi-system symptoms that come and go and may worsen with stress or illness
• Improvement with mast cell medications, known as a medication trial
• Lab tests for chemical mediators like methylhistamine or prostaglandins, taken during a symptom flare
• Ruling out other conditions with similar symptoms, such as asthma or ME/CFS

There’s currently no genetic test for MCAS, but research is ongoing.

Living with MCAS

Living with Mast Cell Activation Syndrome can be challenging, especially when symptoms are unpredictable and vary from day to day. You may find yourself reacting to things that never used to be a problem - like certain foods, fragrances, temperature changes, or stress - and it can take time to identify your personal triggers.

Many people with MCAS go through periods of trial and error while learning how to manage their condition. Finding the right combination of medication, lifestyle adjustments, and support can make a real difference. This might include pacing your activities, keeping a symptom diary, avoiding known triggers, or working with healthcare professionals who understand mast cell conditions.

Find out more about managing MCAS here.

First steps after diagnosis

Receiving a diagnosis of Mast Cell Activation Syndrome can bring a mix of emotions - relief at having an explanation, but also uncertainty about what comes next. It’s normal to feel overwhelmed at first, but there are steps you can take to begin building a sense of control and confidence.

Start by learning as much as you can at a pace that works for you. Keeping a symptom and trigger diary can help you and your doctors spot patterns over time. Many people begin treatment by introducing medications slowly and carefully, as those with MCAS can be sensitive to changes. Your healthcare team may suggest a “low and slow” approach to dosing, which is often more successful.

Where to get support

You don’t have to face MCAS alone. Support can make a real difference - whether you're newly diagnosed or have been managing symptoms for a while.

At Mast Cell Action, we offer a range of free support services to help you feel heard, understood, and connected. These include:

• Online events, peer support groups and webinars on topics like symptom management, pacing, and self-advocacy
• One-to-one support for those needing tailored guidance

• A private Facebook community offering day-to-day encouragement and shared experience

What you’ll find here

Resources on this page will help you:

• Understand what mast cells are and how MCAS affects the body
• Recognise common symptoms and triggers
• Learn about diagnosis and treatment approaches
• Find practical next steps after diagnosis

You are not alone. Many people with MCAS take time to find answers, but support and understanding can make a real difference.