Mastocytosis is a rare condition caused by an excess number of mast cells gathering in the body's tissues.

Mast cells

Mast cells are produced in the bone marrow (the spongy tissue found in the hollow centres of some bones).

Mast cells live longer than normal cells. They're an important part of the immune system and help fight infection.

They are found in parts of the body that are vulnerable to infection, such as the skin, stomach and lining of the lungs.

When mast cells detect an allergen (a substance that triggers an allergic reaction), they release histamine and other chemicals into the bloodstream. Histamine makes the blood vessels expand and the surrounding skin itchy and swollen.

Mast cells sometimes mistake harmless substances, such as pollen, for infectious germs, and trigger the process of swelling (inflammation).

This can cause the skin to become red, swollen and itchy, and it can also create a build-up of mucus in the airways, which become narrower. This is known as an allergic reaction.

Read more about the symptoms of mastocytosis.

Types of mastocytosis

There are two main types of mastocytosis  cutaneous mastocytosis and systemic mastocytosis.

Cutaneous mastocytosis

In cutaneous mastocytosis, mast cells gather in the skin but aren't found in large numbers elsewhere in the body.

Cutaneous mastocytosis mainly affects children, with three-quarters of cases occurring in children who are between one and four years of age. It's also known as paediatric mastocytosis.

The most common symptom of cutaneous mastocytosis is abnormal growths (lesions) on the skin, such as bumps and spots, which can form on the body and can sometimes blister.

Systemic mastocytosis

In systemic mastocytosis, mast cells gather in body tissues, such as the skin, organs and bones. The condition mainly affects adults.

Some people with systemic mastocytosis may experience episodes of severe symptoms that last 15-30 minutes. Many people don't have any problems.

During an episode you may have:

  • skin reactions  such as itching and flushing
  • gut symptoms  such as vomiting and diarrhoea
  • muscle and joint pain
  • mood changes, headaches and episodes of fatigue (tiredness)

The episodes are often triggered by:

There are three subtypes of systemic mastocytosis. They are:

  • indolent mastocytosis  symptoms are usually mild to moderate and vary from person to person; indolent mastocytosis accounts for around 90% of adult systemic mastocytosis cases
  • aggressive mastocytosis  where mast cells multiply in organs, such as the spleen, liver and digestive system; the symptoms are more wide-ranging and severe, although skin lesions are less common
  • systematic mastocytosis with associated blood (haematological) disease  where a condition that affects the blood cells, such as chronic leukaemia, also develops

Severe allergic reaction

People with mastocytosis have an increased risk of having a severe and life-threatening allergic reaction. This is known as anaphylaxis.

The increased risk of anaphylaxis is due to the abnormally high number of mast cells and their potential to release large amounts of histamine into the blood.

If you or your child has mastocytosis, you may need to carry an adrenaline injection pen, which can be used to treat the symptoms of anaphylaxis

What causes mastocytosis?

The cause or causes of mastocytosis aren't fully known, but there's thought to be an association with a genetic mutation known as the "kit mutation".

Genetic mutations occur when the normal instructions carried in certain genes become "scrambled". This results in some of the body’s processes not working normally.

Read more about the causes of mastocytosis.

Diagnosing mastocytosis

A physical examination of the skin is the first stage in diagnosing cutaneous mastocytosis.

Your child’s GP or dermatologist (skin specialist) may rub the affected areas of skin to see if they become red, inflamed and itchy (known as Darier’s sign).

It's usually possible to confirm a diagnosis by carrying out a biopsy (where a small skin sample is taken and checked for mast cells).

Five tests are commonly used to look for systemic mastocytosis. They are:

  • a full blood count (FBC)
  • measuring blood tryptase levels
  • an ultrasound scan to look for enlargement of the liver and spleen
  • DEXA scan to measure bone density 
  • a bone marrow biopsy test

A diagnosis of systemic mastocytosis is usually made by finding typical changes on a bone marrow biopsy.

Read more about diagnosing mastocytosis.

Treating mastocytosis

There's no cure for mastocytosis, so the aim of treatment is to try to relieve the symptoms.

Treatment options will depend on the type of mastocytosis and severity of symptoms.

Mild to moderate cases of cutaneous mastocytosis can be treated with steroid cream (topical corticosteroids). Steroid cream reduces the number of mast cells that can release histamine and trigger swelling (inflammation) in the skin.

Antihistamines can also be used to treat the symptoms of cutaneous or indolent mastocytosis, such as red skin and itchiness. Antihistamines are a type of medication that block the effects of histamine. They're often used to treat allergic conditions.

Read more about treating mastocytosis.


In children, the symptoms of cutaneous mastocytosis usually improve over time, but remain stable in adults. In most cases, the condition gets better on its own by the time a child has reached puberty.

The outlook for systemic mastocytosis can vary, depending on the type you have. Indolent systemic mastocytosis shouldn't affect life expectancy, but other types can. Some people develop a serious haematological condition, such as chronic leukaemia.

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