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 that helps you fight off infections. There are more of them in the skin, the lungs and the 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. We don't know why some people have too many mast cells. We do know some things that trigger the release of histamine from mast cells and cause the symptoms of mastocytosis. Symptoms may be triggered by cold or heat, certain medicines, emotional stress and insect bites.