Mastocytosis Make an Appointment Find a Doctor Ask a Question Reviewed by the National Institute of Allergy and Infectious Diseases (July 01, 2009) Mastocytosis is caused by an excess of mast cells, which are part of the immune system, throughout the body. They release chemical signals (such as histamine) to direct other parts of the immune system to specific areas of the body where they are needed to defend against disease. Mast cells are frequently found in the skin, lymph nodes, internal organs, and the lining of the lung, stomach, and intestine. Mast cells may also be important in healing wounds. For example, when scabs itch, it may be due to the histamine released by mast cells. Researchers also think mast cells may have a role in the growth of blood vessels. No one has ever been found to have a lack or absence of mast cells, so many scientists have concluded that they are critical for life. Programs & Services Allergy & Clinical Immunology (Adult) Clinical Trials For more than 100 years, National Jewish Health has been committed to finding new treatments and cures for diseases. Search our clinical trials.