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. They help you fight off infections. There are more of them in the skin, the lungs and the intestines.
Mast cells make a chemical called histamine.
Histamine can cause swelling, itching and redness when your body reacts to something like an insect bite or a bee sting. We don't know what causes mastocytosis. We do know some things that trigger the release of histamine and cause symptoms. Symptoms may be triggered by cold or heat, certain medicines, emotional stress and insect bites. The triggers aren't the same in every person.