Heat Hives on the Legs: What to Know

Cholinergic urticaria may show as small bumps on the thighs, calves, or around the knees during a rise in body temperature. It can sting or itch, and the visible spots may change as the episode continues. Tight clothing, heat trapped under sportswear, shaving products, insect bites, and skin irritation can produce look-alike rashes. A rash limited to one area or linked to a new product may need a different explanation. Photographing the skin while it is visible can help a clinician assess a short-lived episode.

Stop exercising and rest in a cool setting. Loosen warm clothing, use a cool damp cloth, and avoid hot baths, vigorous rubbing, and scratching. Wash off sweat gently and choose breathable clothing once the skin is comfortable. Keep a record of activity, temperature, clothing, medicines, and how the rash behaved after cooling. If attacks recur, ask a clinician or pharmacist about an oral antihistamine that suits you; [Antihistamine Treatment](/treatments/medical-dermatology/oral-antihistamine-therapy/) covers this treatment approach. Check advice before using it for a child, during pregnancy, or with other medicines.

Call emergency services for breathing trouble, wheezing, throat or tongue swelling, faintness, or sudden collapse. A heat-related trigger does not make these symptoms harmless. Arrange a clinical review if leg swelling is painful or one-sided, the skin becomes hot and tender, blisters, bruises, or stays changed after cooling, or episodes repeatedly disrupt walking or exercise. Prompt assessment is also sensible when a new rash follows a medicine or food.

Does the rash fit cholinergic urticaria or irritation from clothing? Should I change how I exercise in heat? What symptoms require emergency action? Is an oral antihistamine suitable for me? Could my medicines or another condition be contributing?