Mastocytosis is caused by too many mast cells in the body. This most commonly happens in skin. When limited to skin it is called "cutaneous mastocytosis."

Mast cells are also found in organs such as lymph nodes, spleen, liver, and in the lining of the stomach, lungs, and intestines. When organs are involved it is called "systemic mastocytosis."

These cells are important in fighting disease. They release chemical signals (such as "histamine") to alert other immune cells to potential dangers.

When there are too many mast cells, too many chemical signals are released.

The chemicals released by mast cells can cause:

• itching
• flushing (redness of skin)
• headache
• dizziness
• rapid heart beat
• stomach cramping
• nausea
• vomiting
• muscle pain
• diarrhea
• skin rash

In severe cases, the person may have a drop in blood pressure or go into shock.

Certain activities can cause mast cells to release their chemical signals. Activities may include physical exertion, stress, bee stings, certain foods, rubbing or scratching skin, and extremes in temperature.

The rash produced in cutaneous mastocytosis can take several forms. In a type called "urticaria pigmentosa," numerous oval or round, red-brown spots can become itchy, red, and swollen when the skin is stroked or rubbed. This is called the "Darier sign."

In a rarer type, called "telangectasia macularis eruptive perstans," there are fewer mast cells, but hundreds of tiny blood vessels, called "telangectasia." These vessels usually do not become itchy and swollen when the skin is stroked.

In another type, there is a single lesion, called a "mastocytoma." It turns red and swells when stroked.

Tests for mastocytosis may include blood tests, skin biopsy, and bone marrow examination.

Treatment can include antihistamines to relieve itching and steroid creams for the rash. Oral (by mouth) steroids may be needed in severe cases. Epinephrine may be needed in cases of shock.