Understanding a skin rash on the back

Small spots after heat or exercise may reflect blocked sweat ducts. Areas under straps or against a new fabric suggest friction or contact irritation. Scaly patches with a clearer centre can occur with ringworm; thicker defined plaques may fit psoriasis. A widespread rash that follows a new medicine needs prompt review. It can be difficult to see the back clearly, so a mirror or photograph helps track change.

Keep the back cool and dry, wear loose breathable clothing, and rinse away sweat after exercise. Use a mild cleanser and avoid new fragranced products, vigorous scrubbing and picking. Do not share towels or clothing while a contagious infection is possible. Arrange an examination if the rash persists, recurs, or cannot be assessed clearly at home.

Seek urgent care for severe pain, rapidly spreading redness, blistering or peeling, purple spots, fever with a rapidly changing rash, breathing difficulty, or sores involving the mouth or eyes. Prompt review is also sensible when the area becomes hot, swollen, increasingly tender or starts draining.

Does the shape or distribution suggest sweat, contact, fungal or inflammatory disease? Could my clothing, backpack, detergent or medicine be contributing? Is treatment needed, and how should I prevent recurrence?