But medical information is always changing, and some information given here may be out of date. For regularly updated information on a variety of health topics, please visit familydoctor.org , the AAFP patient education Web site. An article on this topic is available in this issue of AFP . It's caused by having too many mast cells.
Mast cells are a kind of blood cell.
Mastocytosis can occur at any age. It's more serious in adults. It's usually mild in children, and they often outgrow it. Mast cells are made by your bone marrow. They're part of your immune system.