Systemic Mastocytosis -

Systemic mastocytosis is a rare condition that results in too many mast cells building up in the body. Mast cells are found in tissues throughout the body. Mast cells help the immune system work properly and help protect the body from disease.

Systemic mastocytosis causes too many mast cells to build up in the skin and bone marrow. Less often, mast cells also build up in the digestive tract or other body organs.

When triggered, these mast cells let out too much histamine and other chemicals into the body, which can cause symptoms like those of an allergic reaction. Sometimes, severe swelling and irritation, called inflammation, results in organ damage. Common triggers include alcohol, insect stings, physical and emotional stress, and certain medicines.

Symptoms of systemic mastocytosis depend on the part of the body affected. Too many mast cells can build up in the skin, bone marrow, liver, spleen or intestines. Less commonly, other organs such as the brain, heart or lungs may be affected.

Symptoms of systemic mastocytosis may include:

Flushing, itching or raised bumps on the skin called hives.
Dizziness, fainting or headache.
Fast heartbeat or a heartbeat that isn’t regular.
Stuffy nose, shortness of breath or a whistling sound when breathing out called wheezing.
Belly pain, diarrhea, upset stomach or vomiting.
Bone or muscle pain.
Severe tiredness.
Depression, irritability, anxiety, or trouble thinking and paying attention.
Bigger than usual liver, spleen or lymph nodes.

Types of systemic mastocytosis

Systemic mastocytosis most commonly occurs in adults. The condition usually includes skin symptoms and affects at least one other organ such as the bone marrow, liver or digestive tract.

The main types of systemic mastocytosis include:

Indolent systemic mastocytosis. This is the most common type. Skin symptoms are common. Other organs may be affected, but the condition usually doesn’t affect how well organs work. This type may worsen slowly over time.
Smoldering systemic mastocytosis. This type involves more-serious symptoms. It may affect how organs work, and the condition worsens over time.
Bone marrow mastocytosis. This type affects only the bone marrow and does not have skin symptoms. Too many mast cells in the bone marrow cause allergic reaction symptoms that happen often and can be severe. This type also causes weakened and brittle bones, called osteoporosis.

Advanced systemic mastocytosis is rare and includes these types:

Systemic mastocytosis with a myeloid or hematologic neoplasm. This is systemic mastocytosis along with a blood or bone marrow condition, such as cancer. This severe type develops rapidly. It affects how well organs work and can cause organ damage.
Aggressive systemic mastocytosis. This type has severe symptoms. It usually affects how well organs work and causes organ damage.
Mast cell leukemia. This is a very rare and aggressive form of systemic mastocytosis.

Skin mastocytosis

Skin mastocytosis, also called cutaneous mastocytosis, typically occurs in children and usually affects only the skin. Cutaneous mastocytosis generally doesn’t lead to systemic mastocytosis. For children, skin symptoms often go away during the teen years. This type also can occur in adults.

When to see a doctor

Talk to your healthcare professional if you have flushing or hives or if you have concerns about other symptoms that could be mastocytosis.

Most often systemic mastocytosis is caused by a random change in the KIT gene. Usually, this change in the KIT gene is not passed down in families.

The gene change causes the body to make too many mast cells. These cells build up in tissues and organs. When triggered, the mast cells let out chemicals into the body, such as histamine, leukotrienes, tryptase and cytokines. These chemicals cause inflammation and symptoms like those of an allergic reaction.

Having a change in the KIT gene is a risk factor for mastocytosis. For people with mastocytosis, being around triggers can raise the risk of symptoms. When triggered, mast cells let out chemicals into the body that cause inflammation and symptoms like those of an allergic reaction. People have different triggers, but the most common ones include:

Insect stings.
Skin irritation.
Sudden temperature changes.
Emotional stress.
Exercise or physical strain.
Certain medicines.
Alcohol.

Complications of systemic mastocytosis can include:

Severe allergic reaction. Called anaphylaxis, this severe allergic reaction includes symptoms such as rapid heartbeat, trouble breathing, fainting, loss of consciousness and shock. Anaphylaxis may lead to death if not treated right away. If you have a severe allergic reaction, you may need a shot of epinephrine.
Blood disorders. These can include not having enough red blood cells, called anemia, and poor blood clotting that can result in bleeding.
Peptic ulcer disease. Ongoing stomach irritation can lead to ulcers and bleeding in the digestive tract.
Low bone density. Because systemic mastocytosis can affect the bones and bone marrow, this may raise the risk of bone conditions such as osteoporosis.
Organ failure. A buildup of mast cells in body organs can cause inflammation and damage to the organs.

To diagnose systemic mastocytosis, your healthcare professional talks with you about your symptoms and medical history, including any medicines you’ve taken. Tests look for high levels of mast cells or the chemicals they let out into the body. Any organs that may be affected by the condition can be checked.

Tests may include:

Blood or urine tests.
Bone marrow biopsy. A biopsy is removing a small sample of tissue for testing in the lab.
Skin biopsy.
Imaging tests such as an X-ray, ultrasound, bone density scan and CT scan.
Checking organs affected by the condition, such as the liver. This may involve doing a biopsy, if needed.
Genetic testing.

Treatment may vary, depending on the type of systemic mastocytosis and the body organs affected. Treatment generally includes controlling triggers to avoid symptoms, treating the condition with options such as medicines, chemotherapy and stem cell transplant, and regular monitoring.

Controlling triggers

Identifying and avoiding factors that may trigger your mast cells, such as medicines or insect stings, can help you manage your systemic mastocytosis symptoms.

Medicines

Your healthcare professional may recommend medicines to:

Treat allergic reaction symptoms, for example, with antihistamines.
Lessen stomach acid and discomfort in your digestive system.
Lessen the effects of the chemicals let out into your body by mast cells, for example, with corticosteroids.
Control the KIT gene to lessen the number of mast cells made.
Lessen bone loss.
Lessen symptoms of depression or anxiety, for example, with antidepressants.

A healthcare professional can teach you how to give yourself an epinephrine shot if needed. The shot helps if you have a severe allergic response when your mast cells are triggered.

Chemotherapy

If you have aggressive systemic mastocytosis, or systemic mastocytosis with a blood or bone marrow condition, you may be treated with chemotherapy medicines to lower the number of mast cells in your body.

Stem cell transplant

In leukemia-related systemic mastocytosis, a stem cell transplant may be an option.

Regular monitoring

Your healthcare professional regularly monitors your condition using blood and urine tests. You may be able to use a special home kit to collect blood and urine samples while you’re having symptoms. This gives your healthcare professional a better picture of how systemic mastocytosis affects your body. Regular bone density measurements can look for bone loss or signs of osteoporosis.

References

Ferri FF. Mastocytosis. Ferri’s Clinical Advisor 2025. Elsevier; 2025. https://www.clinical key.com. Accessed April 1, 2025.
AskMayoExpert. Systemic mastocytosis. Mayo Clinic; 2024.
Gulen T. Management of mediator symptoms, allergy, and anaphylaxis in mastocytosis. Immunology and Allergy Clinics of North America. 2023; doi:10.1016/j.iac.2023.04.010.
Valent P, et al. World Health Organization classification and diagnosis of mastocytosis: Update 2023 and future perspectives. Immunology and Allergy Clinics of North America. 2023; doi:10.1016/j.iac.2023.04.011.
Farmer I, et al. Systemic mastocytosis: State of the art. Current Hematologic Malignancy Reports. 2024; doi:10.1007/s11899-024-00737-8.
Mastocytosis and mast cell activation syndrome. Merck Manual Professional Version. https://www.merckmanuals.com/professional/immunology-allergic-disorders/allergic-autoimmune-and-other-hypersensitivity-disorders/mastocytosis-and-mast-cell-activation-syndrome. Accessed April 1, 2025.
Pardanani A. Systemic mastocytosis in adults: 2023 update on diagnosis, risk stratification and management. American Journal of Hematology. 2023; doi:10.1002/ajh.26962.
Pardanani A, et al. Advanced systemic mastocytosis — Revised classification, new drugs and how we treat. British Journal of Haematology. 2024; doi:10.1111/bjh.19245.
Radia DH, et al. Update on diagnostic approaches and therapeutic strategies in systemic mastocytosis. Best Practice & Research Clinical Haematology. 2022; doi:10.1016/j.beha.2022.101380.
Medical review (expert opinion). Mayo Clinic. April 17, 2025.

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Systemic Mastocytosis

Types of systemic mastocytosis

Skin mastocytosis

When to see a doctor

Controlling triggers

Medicines

Chemotherapy

Stem cell transplant

Regular monitoring

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