Systemic mastocytosis (mas-to-sy-TOE-sis) is an uncommon condition in which too many mast cells accumulate in the body. Mast cells are a kind of white blood cell. Mast cells can be found in connective tissues all over your body. Mast cells aid in the efficient functioning of your immune system and, in most cases, help shield you from disease. Excess mast cells accumulate in your skin, bone marrow, digestive tract,  Read More