Mastocytosis is a genetic immune disorder in which certain cells (mast cells) grow abnormally and cause a range of symptoms, including diarrhea and bone pain. You can't prevent it, but you can avoid triggers and get treatment.


What is mastocytosis?

Mastocytosis is a condition where certain immune cells, called mast cells, build up under the skin and/or in the bones, intestines and other organs.

This abnormal growth of mast cells causes a range of symptoms, including itchy bumps on the skin, gastrointestinal (GI) issues such as diarrhea, and bone pain. It can increase the risk of anaphylaxis (a severe allergic response) when patients come across certain environmental triggers (such as a bee sting). In some cases, the mastocytosis can be aggressive and lead to death if left untreated. Mastocytosis is not contagious.


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What are mast cells?

Mast cells are type of white blood cells located all over your body. People have the highest numbers of mast cells where the body meets the environment: the skin, lungs and intestinal tract.

Normally, mast cells are part of your immune system. When mast cells detect a germ or virus, they set off an inflammatory (allergic) response by releasing a chemical called histamine. This response protects your body from germs and infections.

Mast cells are also involved with other vital functions in your body. They are part of wound healing, bone growth and forming new blood vessels.

What are the types of mastocytosis?

There are two main types of mastocytosis. They are:

  • Cutaneous: This type of mastocytosis affects the skin only. It occurs more often in children. Mast cells build up in the skin, causing red or brown lesions that itch. By itself, cutaneous mastocytosis isn’t life-threatening. But people with the disorder have significant symptoms and have a much higher risk of a severe allergic reaction, which can be fatal.
  • Systemic: Occurring mainly in adults, systemic mastocytosis affects parts of the body other than the skin. Mast cells accumulate in the bone marrow and organs, such as the intestines. In cases of aggressive systemic mastocytosis, it can be life-threatening. Systemic mastocytosis includes two rare forms: mast cell leukemia and mast cell sarcoma. Mast cell sarcoma occurs when a tumor made up of mast cells forms somewhere in the body. Mast cell leukemia is a very aggressive form of the disease where large numbers of mast cells are found in the blood and bone marrow.

Symptoms and Causes

What causes mastocytosis?

Mastocytosis, in particular systemic mastocytosis, is often caused by a mutation (a change in the code or sequence) in a gene called KIT. The change happens after conception. In most cases, it is not inherited (passed down from one generation to another).

If you have mastocytosis, certain activities and factors can trigger an attack. What causes an attack for one person may not affect someone else. There are dozens of potential triggers. You should talk to your doctor about medications and situations you should avoid.

Some common triggers include:

Who does mastocytosis affect?

Mastocytosis can occur in children and adults. Systemic mastocytosis usually affects adults. Cutaneous mastocytosis typically appears in children, usually before the child’s second birthday. The condition affects males and females mostly equally.


How common is mastocytosis?

Mastocytosis is rare. One estimate reports that it occurs in one in every 10,000 people, while another estimate is one in every 20,000 people.

What are the symptoms of mastocytosis?

Symptoms of mastocytosis can range from mild to severe. They include:

  • Brown or red blotches on the skin, or bumps or spots that itch.
  • Skin blisters (this symptom usually occurs in children).
  • Nausea, stomach pain, diarrhea and vomiting.
  • Bone pain.
  • Flushing (when skin all over the body turns red).
  • A drop in blood pressure.
  • Fainting.

Diagnosis and Tests

How is mastocytosis diagnosed?

Your healthcare provider will ask about your symptoms and examine your skin. They may order urine or blood tests. To diagnose cutaneous mastocytosis, your provider will take a small skin sample and send it to a lab for testing. This procedure is called a skin biopsy.

Doctors may perform a bone marrow biopsy if they think you have systemic mastocytosis. They insert a needle into your bone and remove a sample of the bone marrow (spongy tissue inside your bones) and bone tissue. Your doctor will numb the area before the procedure. Before a biopsy, your healthcare provider may order a blood test to measure the basal serum total tryptase level. Mast cells release tryptase, an enzyme, when the cells are triggered.

Management and Treatment

How is mastocytosis treated?

There is no cure for mastocytosis, but treatments can help minimize symptoms. To manage it, you’ll need to avoid triggers that might cause an attack. Treatment for mastocytosis includes:

  • Medications for symptoms: Antihistamines, leukotriene modifiers, mast cell stabilizers and corticosteroid creams can relieve the symptoms of an allergic reaction, such as itchy skin lesions. To reduce inflammation, doctors may prescribe oral steroids or a drug called cromolyn sodium. Bisphosphonates can strengthen weak bones. Depending on your symptoms, your doctor may prescribe other medications, including drugs that reduce stomach acid or relieve bone pain.
  • Epinephrine: Everyone who has mastocytosis should carry an EpiPen® (injectable epinephrine). In case of anaphylactic shock, an epinephrine injection could save your life.
  • Ultraviolet light: Your doctor may use ultraviolet (UV) light to make darkened skin lesions less noticeable.
  • Treatments for aggressive systemic mastocytosis: Your doctor may prescribe chemotherapy such as cladribine to treat aggressive systemic mastocytosis. Midostaurin, a drug that targets the KIT mutation has been approved by the US FDA for the treatment of systemic mastocytosis. For those without a mutation in the KIT gene, another medication called imatinib can be used. Some patients with aggressive systemic mastocytosis may undergo an allogeneic hematopoietic stem cell transplant (also called a bone marrow transplant). A new medication that targets the KIT mutation, called avapritinib, while not approved by the US FDA, may be available in certain circumstances.

What are the complications of mastocytosis?

People with mastocytosis have a much higher chance of a life-threatening allergic reaction. Triggers such as medications, foods, and sudden changes in temperature (like jumping into cold water) can cause anaphylactic shock.

If you or your child has mastocytosis, you should talk to your doctor before you receive anesthesia. Many types of anesthesia can trigger a fatal allergic reaction.

Complications of systemic mastocytosis include:

  • Soft, weak bones: A condition called osteoporosis causes bones to soften and break down.
  • Liver problems: The liver can become inflamed and may not work as well.
  • Cytopenia: Mastocytosis can decrease the number of blood cells your body produces, a condition called cytopenia. Cytopenia can lead to fatigue, weakness, or excessive bleeding and bruising. It can also make you more vulnerable to infection.
  • Cancer: Rarely, people develop mast cell leukemia or mast cell sarcoma (cancer of the body’s soft tissues).


How can you prevent mastocytosis?

Because mastocytosis is a genetic condition, there is no way to prevent it. If you have mastocytosis, you may be able to prevent an attack by avoiding foods, medications, and situations that trigger an outbreak.

Talk to your doctor about the triggers you should avoid. Triggers vary from person to person. Consider wearing a medical alert bracelet to notify others about medicines (such as anesthesia) you cannot take.

Outlook / Prognosis

What is the outlook for people with mastocytosis?

The outlook depends on the type of mastocytosis and how severe it is. Cutaneous mastocytosis is not life-threatening, but children who have it have a higher chance of a fatal allergic reaction. Cutaneous mastocytosis in children usually goes away or gets better by the time the child reaches puberty. This is why aggressive treatment is usually not necessary.

Systemic mastocytosis affects organs all over the body. That means it’s often more serious than cutaneous mastocytosis. The prognosis varies widely because systemic mastocytosis can range in severity.

People who have more aggressive cases of mastocytosis may not survive more than a few years after diagnosis. People with less aggressive mastocytosis have a typical life expectancy. They can usually manage the condition by avoiding triggers and taking antihistamines.

Medically Reviewed

Last reviewed by a Cleveland Clinic medical professional on 09/17/2020.

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