Why do I get hives when I exercise?

Breaking out in itchy bumps mid-workout is a recognised pattern, and the usual explanation is heat. The NHS lists hot, sweaty skin from exercise among the triggers for hives: rising body temperature and sweating prompt the release of histamine and other chemicals in the skin, producing raised, itchy wheals - often small and numerous, scattered across the chest, neck, and arms, sometimes called cholinergic urticaria when heat is the specific driver. MedlinePlus confirms exercise as a hives trigger and notes a reassuring feature: wheals often change shape, disappear, and reappear within minutes or hours. The typical episode peaks during the workout and fades within 30 to 60 minutes of stopping and cooling down - that fast fade is the signature of the harmless version. Management is about turning the heat down: exercise in cooler rooms or cooler hours, wear light breathable kit, warm up gradually so the temperature rise is slower, and keep showers lukewarm rather than hot afterwards. A non-sedating antihistamine before exercise, taken with a pharmacist's advice, helps many people with a recurring pattern. Two cautions matter. First, the emergency version: hives with swelling of the lips, tongue, or face, wheezing, dizziness, or feeling faint during exercise is a possible severe allergic reaction - stop and get urgent help; exercise can amplify food allergies into this. Second, hives appearing daily for over six weeks regardless of exercise deserve a GP look for underlying causes. The plain heat-hives pattern, though, needs no treatment beyond cooling strategies. Pymander is a free AI doctor, 24/7 by text, that can help you pin down your trigger.