What is Mast Cell Activation Syndrome?

MCAS is a condition involving mast cells, which are an important part of the immune system that help the body respond to things such as infection, injury and other potential threats. Mast cells release chemical substances called mediators as part of this response. In MCAS, mast cells become activated inappropriately or excessively and release these mediators too readily, in excessive amounts or in response to triggers that would not usually cause a problem.

This can lead to a wide range of symptoms, which may come and go, change over time and vary considerably from person to person. MCAS can develop in both children and adults.

Why can MCAS affect so much of the body?

Mast cells are found in tissues throughout the body, so the effects of mast cell activation can be widespread. Symptoms typically affect several different body systems and can look very different from one person to another.

For some people symptoms are relatively manageable. For others, MCAS can have a substantial impact on everyday life.

Our understanding of MCAS continues to develop as more research is carried out.

Learn more about mast cells and mediators.

Symptoms and triggers

MCAS can cause symptoms across many different body systems. They may come and go, change in severity and sometimes affect several parts of the body at once. Find out more about MCAS symptoms here.

Triggers are also very individual and can change over time even within the same individual. These can include foods, fragrances, medications, infections, temperature changes, exercise, hormones and stress. Explore more information about triggers here.

If you are wondering if your symptoms might be MCAS, you can read more here.

Testing and diagnosis

Getting a diagnosis of MCAS can take time. There is no single test that can confirm MCAS in every person, and many of its symptoms can also occur in other conditions. Because symptoms typically affect many different parts of the body, people may see several different specialists, each focusing on one set of symptoms rather than the overall pattern. This can make it harder for the full picture to be recognised.

Diagnosis typically involves looking at your symptoms and medical history, test results, response to treatment and whether there could be another explanation for your symptoms. Explore more information about testing and diagnosis here.

Managing MCAS

There is no single approach to managing MCAS that works for everyone.

Management may include medication, understanding and reducing individual triggers, making practical adjustments and planning for times when symptoms become more difficult.

Finding the right approach can take time, and your needs may change as your symptoms change.

Explore managing MCAS here.

Living with MCAS

MCAS can affect much more than physical symptoms. It can influence work or education, relationships, eating, exercise, sleep, social activities and everyday plans.

Much of this impact can be invisible to others, but that doesn't make it easier to cope with. Hearing from people with lived experience can help people feel less alone, share practical ways of coping and build a greater sense of understanding and connection.

Read a selection of our community's stories here.

You are not alone. If you need support, find out how we can help here.

Help us change what it means to live with MCAS

Too many people affected by MCAS still struggle to find reliable information, appropriate support and understanding.

Mast Cell Action provides information, practical resources and support while working to improve awareness, research, diagnosis, treatment and care. But we can't do it without you. Your donation helps us be there for people today while working towards a better future for everyone affected by MCAS.

Find out more about donating to Mast Cell Action or fundraising to support this vital work.