What should you know about whole body rash?

A rash may look like flat or raised patches, small bumps, welts, blisters, scaling, or peeling. It can itch, burn, feel tender, or cause no sensation. New soap, detergent, cosmetics, plants, heat, sweating, or friction can irritate skin. Conditions such as atopic dermatitis, contact dermatitis, heat rash, psoriasis, intertrigo, ringworm, and scabies can also produce rash-like changes. A drug rash may begin after starting, stopping, or changing a medicine, including a product bought without a prescription. The pattern, body areas involved, and speed of spread help a clinician narrow the possibilities.

Note when the rash began and photograph it in good light so changes can be compared. List every new medicine, supplement, skin product, detergent, food, and recent exposure. Use lukewarm water, a bland fragrance-free moisturiser, and loose breathable clothing. Avoid scratching, harsh scrubs, hot showers, and starting steroid or antibiotic creams without advice. If a medicine may be involved, contact the prescriber before making a change, unless emergency symptoms require immediate help.

Seek emergency help for trouble breathing, swelling of the lips or tongue, faintness, blistering, skin peeling, severe skin pain, or sores involving the mouth, eyes, or genitals. Arrange prompt medical assessment if the rash is rapidly spreading, accompanied by fever or significant illness, or appears after a new medicine. A clinician can examine the skin and decide whether testing or prescription treatment is needed.

Which features make one cause more likely than another? Could a medicine, infection, allergy, or product be contributing? What should I stop using, and which treatments are safe for my skin? What changes should prompt urgent review?