How Mast Cells Respond to Parasites

Dr. Theoharis Theoharides explains that mast cells are front‑line immune cells that evolved primarily to defend us against parasites, but they also react to many non‑allergic triggers such as infections, toxins (like mold and heavy metals), physical or emotional stress, and trauma. When a parasite or other trigger is detected, mast cells release a wide array of mediators (histamine, cytokines, proteases, and many others) that help fight invaders and coordinate the wider immune response. In some people, especially after a major stressor, infection, or environmental exposure, these cells can become dysregulated and over‑reactive, firing too easily and too strongly. This can present as new or worsening allergies, food and chemical sensitivities, gastrointestinal upset, brain fog, pain, flushing, palpitations, and other MCAS‑type symptoms. For patients with POTS or EDS, this overactivity can worsen autonomic symptoms and pain and may be a key comorbidity. Clinically, understanding mast cells as broad danger sensors—not just ‘allergy cells’—helps guide management: reducing cumulative triggers (such as mold, heavy metals, and chronic stress), stabilizing mast cells with medications or supplements, and addressing underlying infections or toxic exposures can be important steps in calming the system and preventing escalating sensitivity after major life or health stressors.