What can MCAS symptoms look like?

MCAS can cause a wide range of symptoms because mast cells are found throughout the body and release multiple different chemicals during a reaction. Symptoms typically affect several body systems at the same time and can vary considerably from person to person.

They may include flushing, itching or hives, digestive symptoms, headaches, brain fog, fatigue, palpitations, dizziness, breathing difficulties and allergy-type reactions. Some people experience relatively mild symptoms, while for others they can have a significant impact on everyday life.

Symptoms can change over time

MCAS symptoms often fluctuate. You may have periods when symptoms are relatively stable and other times when they become more frequent, severe or affect different parts of your body. This is often referred to as 'a flare' or 'flare-up'.

Symptoms can also change over time. Some people notice a gradual change, while others experience a significant worsening following an illness, infection, medical procedure or another event.

Understanding your usual pattern can make it easier to recognise when something has changed.

Symptoms can affect different body systems

Mast cells are present throughout the body, so symptoms associated with mast cell activation can occur in many different body systems.

These can include the skin, digestive system, cardiovascular system, respiratory system and nervous system, as well as more general symptoms such as fatigue and pain.

The combination of symptoms experienced is individual - you don't need to experience every symptom or have symptoms affecting every body system.

Keeping track of your symptoms

When symptoms affect several parts of the body or change from day to day, it can be difficult to remember everything you have experienced. Keeping a simple record can help you identify patterns and explain what is happening to a healthcare professional. You might find it helpful to note your main symptoms, when they occur, how long they last, their severity and anything that appears to make them better or worse.

Photographs can also be useful for visible symptoms that may have disappeared by the time of an appointment.

Download our symptom tracker here.

When to seek medical advice

Many symptoms associated with MCAS can also occur in other health conditions. If you have new, persistent, worsening or unexplained symptoms, speak to an appropriate healthcare professional rather than assuming they are caused by MCAS.

Seeking medical advice is particularly important if your usual symptoms change significantly or you develop something new.

If you are currently trying to understand unexplained symptoms, our information can also help you prepare for a conversation with your GP.

Recognising Anaphylaxis

Anaphylaxis is a serious and potentially life-threatening reaction that requires immediate treatment.

Symptoms can develop rapidly and may include difficulty breathing, swelling of the tongue or throat, wheezing, dizziness, collapse or loss of consciousness. Skin symptoms such as hives, flushing or swelling may occur, but are not always present.

If you think you or someone else is experiencing anaphylaxis, follow their emergency treatment plan if they have one and seek emergency medical help. Learn more about anaphylaxis from Anaphylaxis UK.