An immune cell packed with granules of histamine and other chemicals—it triggers allergic reactions and plays a role in wound healing.Mast cells are tissue-resident immune cells containing granules of histamine, heparin, proteases (tryptase, chymase), and cytokines. Degranulation is triggered by IgE crosslinking, complement activation, and neuropeptides (substance P, VIP). Mast cells are central to allergic and anaphylactic responses but also contribute to wound healing, angiogenesis, and host defense. MrgX2 receptor activation by peptides (including cortistatin and some antimicrobial peptides) can trigger non-IgE-mediated mast cell degranulation—a consideration for peptide safety assessment.