If you have systemic mastocytosis, you have too many of the cells involved in allergic reactions, called mast cells. Mastocytosis can be present only in the skin, or you can have numbers of mast cells throughout the body, including the digestive tract and bone marrow. Symptoms of systemic mastocytosis include allergic skin reactions, difficulty concentrating and diarrhea.
Doctors diagnose systemic mastocytosis by taking a small tissue sample called a biopsy. If they find mast cells in parts of the body other than the skin, you have systemic mastocytosis. This disease is usually treated with antihistamines, but systemic mastocytosis can also be treated with chemotherapy.