Systemic mastocytosis (mas-to-sy-TOE-sis) is a disorder caused by a genetic mutation that results in an excessive number of mast cells in your body. Mast cells normally help protect you from disease and aid in wound healing by releasing substances such as histamine and leukotrienes. But if you have systemic mastocytosis, excess mast cells can build up in your skin, around blood vessels, in your respiratory, gastrointestinal and urinary tracts, or in reproductive organs. When triggered, these mast cells release substances that can overwhelm your body and result in symptoms such as facial flushing, itching, a rapid heartbeat, abdominal cramps, lightheadedness or even loss of consciousness. Common triggers include alcohol, temperature changes, spicy foods and certain medications.