What is Mast Cell Activation Syndrome (MCAS)?

Mast Cell Activation Syndrome (MCAS) is a condition that causes mast cells to release an inappropriate amount of chemicals into your body. This causes allergy symptoms and a wide range of other symptoms.

Mast cells are blood cells that are part of your immune system. They help you fight infections, but they are also involved in allergic reactions. Mast cells live longer than normal cells, and they grow in your bone marrow, your gastrointestinal tract, your skin, and your airways. 

When you come into contact with an allergen, or substance that causes allergies, mast cells release chemicals called mediators. Some chemicals are released right away, and some take longer. 

One of those chemicals is histamine, which might cause allergy symptoms. These include:

  • Expanding blood vessels
  • Itchy skin
  • Swollen skin
  • Mucus buildup
  • Tightened airways
  • Wheezing
  • Headaches
  • Anaphylaxis

In a healthy person, these chemicals help protect and heal. In someone with MCAS, they have a negative effect. 

Sometimes mast cells can be activated or triggered by things like:

  • Infections
  • Medications
  • Insect venom
  • Fragrances
  • Stress
  • Exercise
  • Food 

People who have MCAS might have a lot of allergy symptoms and lots of episodes of anaphylaxis without a clear cause. 

Signs and Symptoms

There are many different symptoms that affect lots of your body systems all at once. These can happen after eating foods, smelling certain fragrances, exercising, and many other things. 

Some key signs include:

  • Symptoms in more than one system
  • Symptoms that come and go or are cyclical
  • Lots of different triggers
  • Difficulty figuring out what the triggers are
  • A dramatic change in symptoms 

Some key symptoms include:

  • Swelling
  • Itching
  • Rashes
  • Inflammation
  • Vomiting
  • Headaches
  • Chronic pain
  • Flushing 
  • Diarrhea
  • Constipation
  • Fast heart beat
  • Low blood pressure
  • Fatigue
  • Fainting
  • Sweats
  • Abdominal pain

Diagnosing and Treating Mast Cell Activation Syndrome

Getting diagnosed can be complicated. It’s common for patients to see lots of different doctors. This can happen because there are usually lots of symptoms that might look like other conditions, and it’s hard to pinpoint their exact cause. 

Your doctor might test for Tryptase, Histamine, and Prostaglandin levels, but there are no definitive tests. There are three specific things your doctor will look for, though:

  1. Allergy symptoms and other symptoms in two or more organ systems that keep coming back or are chronic
  2. Higher than normal levels of Tryptase, Histamine, or Prostaglandins in your blood
  3. Getting better after using antihistamine medications or other drugs that block chemicals released by mast cells

If you meet all three of these criteria, your doctor might diagnose you with MCAS. 

There is no cure for the condition. You will need to avoid triggers and may need to use medications to get symptoms under control.

Antihistamine medications and other drugs that block these chemicals can help. These can include:

  • First-generation H1 blockers
    • Diphenhydramine
    • Hydroxyzine
  • Second-generation H1 blockers
    • Loratidine
    • Cetirizine
    • Fexofenadine
  • H2 blockers
    • Ranitidine 
    • Famotidine
  • Leukotriene inhibitors
    • Montelukast
    • Zafirlukast
  • Corticosteroids
  • Monoclonal antibodies
    • Omalizumab

If you have anaphylactic reactions, your doctor might also give you an auto-injector epinephrine pen to use in emergencies.

Sometimes people also react to ingredients in the medications, which means it can take some time to find the right treatment. It might be a good idea to look into the Medic Alert Service.

Stress can also cause mast cells to be activated. Plus, having symptoms from MCAS can cause more stress and worry. This can lead to a vicious cycle of symptoms. It’s important to manage your stress.

There is a relationship between Mast Cells and Dysautonomia. One study of patients with EDS and POTs found 66% had symptoms consistent with MCAS, as such there is some speculation that mast cells can be altered as part of a connective tissue disorder such as EDS.

Support for Mast Cell Activation Syndrome

New Zealand Foundation for Mast Cell Activation Disorders is the official Charitable Trust in New Zealand Aotearoa for Mastocytosis and Mast Cell Activation Syndrome.

October 20th is the annual awareness day of Mast Cell Activation Disorders.