Mastocytosis | Overview


What is mastocytosis?

Mastocytosis (say "mass-toe-sigh-toe-sis") is the abnormal growth of mast cells in the body. Mast cells are part of the immune system, which helps protect your body against infection. The most common form of mastocytosis is when mast cells accumulate on the skin, causing reddish-brown spots or bumps. In rare cases, mastocytosis can affect other parts of the body, such as the stomach, the intestines and the bone marrow.

Mastocytosis can occur in people of any age. It is usually mild in children, and they often outgrow it.

What are mast cells?

Mast cells are a kind of cell made by your bone marrow. They're part of your immune system, which helps you fight off infections. There are more of these cells in your skin, lungs and intestines than in other parts of your body.

Mast cells make a chemical called histamine. Normally, this chemical serves as a kind of alarm to let the immune system know that an infection is attacking part of the body. Histamine can cause swelling, itching and redness when your body reacts to something like an insect bite or a bee sting (called an allergic reaction).


Cutaneous and Systemic Manifestations of Mastocytosis by WA Alto, M.D., M.P.H., and L Clarcq, D.O. (American Family Physician June 01, 1999,

Written by editorial staff

Reviewed/Updated: 03/14
Created: 06/99