Heat rash from running: what to know

Exercise increases body temperature and sweat. When sweat stays against the skin, especially beneath tight clothing or in folds, ducts can become blocked and create tiny prickly bumps with itch or stinging. The rash may occur where a shirt, waistband, socks, or sports equipment rubs. This pattern may be [Heat Rash](/conditions/heat-rash/), while broader [Skin Redness](/symptoms/skin-redness/) or [Skin Bumps](/symptoms/skin-bumps/) can have other explanations.

Friction, salt from dried sweat, and a damp fabric layer can keep irritation going after the run. Note whether the rash follows clothing edges, appears during hot weather, or improves after cooling; that information helps separate heat rash from contact irritation or another [Skin Rash](/symptoms/skin-rash/).

Stop in a cool place, rinse away sweat with lukewarm water, and pat dry. Change promptly into loose, breathable clothing. A cool damp cloth can reduce prickling; avoid direct ice, scratching, and thick oily products over the affected area. Wash running clothes after each use and check that seams or straps are not rubbing the same spot.

A plain moisturiser can support dry surrounding skin; [Emollient Therapy](/treatments/medical-dermatology/emollient-therapy/) explains this approach. Ask a clinician before using [Topical Corticosteroids](/treatments/medical-dermatology/topical-corticosteroids/) on a rash that is wet, crusted, or not clearly heat-related. Resume running gradually only when the skin is comfortable and intact.

Seek medical advice if cooling, dry clothing, and reduced friction do not help, if episodes recur despite changing your routine, or if the rash interferes with exercise. Prompt assessment is appropriate for worsening pain, warmth, swelling, pus, yellow crust, fever, rapidly spreading redness, blisters, or red streaks. Emergency help is needed for breathing trouble, facial swelling, faintness, or a rapidly widespread rash with severe illness.

Ask whether the rash is heat rash or contact irritation from fabric, detergent, sunscreen, or a product. Bring details about the route, weather, clothing, timing, and recovery after cooling. Ask how to protect the area during future runs, whether a different fabric or fit may help, and what treatment is appropriate if itch continues.