Mastocytosis: what is it? Mastocytosis is a rare condition in which there are too many mast cells present in the body. Mast cells are a normal part of our immune system, but in mastocytosis, they accumulate. They can cause symptoms by releasing substances such as histamine. There are different forms of mastocytosis. The main distinction is between cutaneous and systemic mastocytosis. Cutaneous mastocytosis In cutaneous mastocytosis, the mast cells are mainly located in the skin. This form is most common in children. The skin often shows spots or bumps that can be itchy or change color. Cutaneous mastocytosis usually remains confined to the skin and sometimes resolves on its own over time. Systemic mastocytosis In systemic mastocytosis, the mast cells are not only in the skin but also in organs such as the bone marrow, intestines, or spleen. This form is primarily found in adults. The symptoms can therefore be broader and less clear, making the diagnosis difficult at times. (translated)