(Mast Cell Disease)

ByJames Fernandez, MD, PhD, Cleveland Clinic Lerner College of Medicine at Case Western Reserve University
Reviewed/Revised Oct 2022 | Modified Mar 2023

Mastocytosis is an uncommon abnormal accumulation of mast cells in the skin and sometimes in various other parts of the body.

  • People may have itchy spots and bumps, flushing, digestive upset, and sometimes bone pain or anaphylactic and anaphylactoid reactions.

  • Symptoms suggest the diagnosis, and a biopsy of the skin and/or bone marrow can confirm it.

  • If mastocytosis affects only the skin, it may resolve without treatment, but if it affects other parts of the body, it cannot be cured.

  • Antihistamines help relieve itching, and histamine-2 (H2) blockers help relieve digestive upset.

(See also Overview of Allergic Reactions.)

Mastocytosis develops when mast cells increase in number and accumulate in tissues over a period of years. Mast cells are part of the immune system and are normally present in many body tissues, particularly the skin, lungs, and lining of the intestine. Mast cells produce histamine, a substance involved in inflammatory and allergic reactions and in the production of stomach acid. Because the number of mast cells increases, levels of histamine increase. Histamine can cause many symptoms, including digestive problems.

Mastocytosis is rare. It differs from typical allergic reactions because it is chronic rather than episodic.

Some people have a genetic mutation that causes mastocytosis. What causes the disorder in others is sometimes unclear.

Types of mastocytosis

There are two main types of mastocytosis:

  • Cutaneous mastocytosis (primarily in the skin)

  • Systemic mastocytosis (affecting organs other than the skin)

Cutaneous mastocytosis usually occurs in children. Occasionally, mast cells accumulate only as a single mass in the skin (mastocytoma), typically before age 6 months. More commonly, mast cells congregate in many areas of the skin, forming small reddish brown spots or bumps (called urticaria pigmentosa). Urticaria pigmentosa rarely progresses to systemic mastocytosis in children but may do so more often in adults.

Systemic mastocytosis usually occurs in adults. Typically, mast cells accumulate in bone marrow (where blood cells are produced). Often, they also accumulate in the skin, stomach, intestine, liver, spleen, and lymph nodes. Organs may continue to function, with little disruption. But if many mast cells accumulate in the bone marrow, too few blood cells are produced, and serious blood disorders, such as leukemia, can develop. If many mast cells accumulate in organs, the organs malfunction. The resulting problems can be life threatening.

Images of Urticaria Pigmentosa
Urticaria Pigmentosa (Infant)
Urticaria Pigmentosa (Infant)
This photo shows small reddish brown bumps covering the body of an infant with mastocytosis.

© Springer Science+Business Media

Urticaria Pigmentosa (Child)
Urticaria Pigmentosa (Child)
This photo shows reddish-brown spots on the back of a school-aged child with mastocytosis.

© Springer Science+Business Media

Urticaria Pigmentosa (Leg)
Urticaria Pigmentosa (Leg)
These yellowish-tan to reddish brown spots and bumps produce a hive when stroked, indicating systemic mastocytosis.

© Springer Science+Business Media

Urticaria Pigmentosa (Chest)
Urticaria Pigmentosa (Chest)
Urticaria pigmentosa may occur as reddish bumps on the skin.

© Springer Science+Business Media

Urticaria Pigmentosa
Urticaria Pigmentosa
In mastocytosis, small reddish brown spots or bumps (called urticaria pigmentosa) may form on the skin.

By permission of the publisher. From Joe E, Soter N. In Current Dermatologic Diagnosis and Treatment, edited by I Freedberg, IM Freedberg, and MR Sanchez. Philadelphia, Current Medicine, 2001.

Mast cell activation syndrome (MCAS) develops when mast cells become overactive and release their contents, which include histamine and other substances that cause inflammation and allergy symptoms. Thus, MCAS, unlike mastocytosis, is not caused by accumulation of excess mast cells in the skin and other tissues. However, symptoms may resemble those of systemic mastocytosis. They may include a rapid heart rate, fainting, hives, flushing, nausea, vomiting, and brain fog. Symptoms may occur frequently and suddenly. MCAS should be diagnosed based on characteristic symptoms, laboratory test results, and a lessening of symptoms in response to treatment for MCAS. People are usually treated with antihistamines, leukotriene inhibitors, and mast cell stabilizers. Whether mast cell activation syndrome progresses to mastocytosis is unclear.

Symptoms of Mastocytosis

A single mastocytoma may not cause symptoms.

Spots and bumps may itch, particularly if they are rubbed or scratched. Itching may be worsened by the following:

  • Changes in temperature

  • Contact with clothing or other materials

  • Use of some drugs, including nonsteroidal anti-inflammatory drugs (NSAIDs)

  • Consumption of hot beverages, spicy foods, or alcohol

  • Exercise

Rubbing or scratching the spots may result in hives and make the skin turn red.

Flushing is common.

Peptic ulcers may develop because too much histamine is produced, stimulating secretion of excess stomach acid. Ulcers can cause stomach pain. Nausea, vomiting, and chronic diarrhea may also occur. Mast cells may accumulate in the liver and spleen, causing them to malfunction. As a result, fluid may accumulate in the abdomen, causing it to enlarge.

If bone marrow is affected, bone pain and anemia can result.

People with mastocytosis may become irritable, depressed, or moody.

Widespread reactions may occur. With systemic mastocytosis, the widespread reactions tend to be severe. They include anaphylactic and anaphylactoid reactions, which cause fainting and a life-threatening drop in blood pressure (shock). Anaphylactoid reactions resemble anaphylactic reactions, but no allergen triggers them.

Systemic mastocytosis may affect bone marrow, and up to 30% of adults with systemic mastocytosis develop cancers, particularly myeloid leukemias. In these people, life expectancy may be shortened.

Diagnosis of Mastocytosis

  • Bone marrow biopsy

  • Sometimes blood tests

Doctors suspect mastocytosis based on symptoms, particularly spots that, when scratched, result in hives and redness.

A bone marrow biopsy can confirm the diagnosis of mastocytosis. Usually, a sample of bone marrow is removed and examined under a microscope to check for mast cells and, if they are present, to determine how many there are and what they look like. Sometimes a skin biopsy can be done to check for mast cells, but a bone marrow biopsy is still needed to check for systemic mastocytosis.

Doctors use specific criteria to diagnose mastocytosis based on results of the bone marrow biopsy, including gene tests for a specific mutation present in many people with mastocytosis, and blood tests.

If the diagnosis is unclear, doctors may do the following:

  • Blood and urine tests to measure levels of substances related to mast cells: High levels support the diagnosis of systemic mastocytosis but do not confirm it.

  • A bone scan

  • Biopsy (using an endoscope) to determine whether the number of mast cells in the digestive tract is abnormally high

Treatment of Mastocytosis

  • Drugs to relieve symptoms

A single mastocytoma may disappear spontaneously.

Itching due to cutaneous mastocytosis may be treated with antihistamines. For children, no other treatment is needed. If adults have itching and rashes, psoralen (a drug that makes the skin more sensitive to ultraviolet light) plus ultraviolet light or corticosteroid creams may be applied to the skin.

Systemic mastocytosis cannot be cured, but symptoms can be controlled with H1 and H2 histamine blockers. (Both of these blockers are antihistamines, but the term antihistamine is usually used only for H1 blockers.) H1 blockers can relieve itching. H2 blockersReye syndrome is a risk.


If many mast cells accumulate in the spleen, the spleen may be removed.

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