Causes of Mast Cell Activation Mast cells are immune cells that release histamine and other chemicals during allergic and inflammatory responses. Overactivation can stem from: • Primary Causes: Genetic conditions like mastocytosis, which lead to excessive mast cells. • Secondary Causes: Environmental triggers such as mold, toxins, stress, medications, infections, or certain foods. • Idiopathic Causes: Episodes of mast cell overactivation without a clear trigger. • Histamine Intolerance: An inabi