What should you know about a rash on your arm?

A flat red patch after a new soap, plant, adhesive or fabric may fit Contact Dermatitis. Dry, itchy areas that recur can occur with Atopic Dermatitis, while thickened, sharply bordered patches with scale may fit Psoriasis. A ring-shaped, expanding patch suggests Ringworm. Tiny itchy bumps after sweating can occur with Heat Rash, and intense itch that is worse at night or affects close contacts raises Scabies as a possibility. A medication can also trigger Drug Rash. The rash pattern does not establish a diagnosis by itself.

Take a clear photo and note when the rash began, whether it is spreading, and anything newly touching the skin. Gently wash with lukewarm water, pat dry, and use a plain fragrance-free moisturiser. Avoid scratching, fragranced products, hot showers and tight sleeves. Do not apply a steroid, antifungal or antibiotic cream repeatedly without advice, because the wrong product can obscure the pattern or irritate skin. A clinician can examine the border, scale, bumps and surrounding skin and choose treatment based on the cause.

Seek urgent medical help if the rash comes with trouble breathing, swelling of the lips or face, faintness, blistering, skin peeling, severe pain, fever, or purple spots that do not fade when pressed. Arrange a prompt assessment if redness is rapidly spreading, the area is warm and tender, pus appears, or a new rash follows a medicine. Book a routine dermatology visit if it persists, keeps returning, or interferes with sleep.

Ask: What features make one cause more likely? Could a recent product, exposure or medicine be involved? Should I stop or change anything I am using? Which symptoms mean I should return sooner? Would a skin scraping, swab or other test help?