What should you know about sudden rash?

A rash may be flat, raised, scaly, blistered, ring-shaped, or located in a fold. Itching after a new soap, fabric, plant, or cosmetic can fit [Contact Dermatitis](/conditions/contact-dermatitis/). Heat and sweating may produce [Heat Rash](/conditions/heat-rash/), while moist skin folds can develop [Intertrigo](/conditions/intertrigo/).

A new medicine can cause a [Drug Rash](/conditions/drug-eruption/), and intense night-time itch affecting household contacts can occur with [Scabies](/conditions/scabies/). Ring-shaped scale may fit [Ringworm](/conditions/ringworm/); recurring thick scale or an itchy dry rash may need assessment for [Psoriasis](/conditions/psoriasis/) or [Atopic Dermatitis](/conditions/atopic-dermatitis/). These patterns overlap, so appearance alone is not enough to diagnose the cause.

Take a clear photograph, note when it began, and list new products, medicines, foods, travel, bites, heat, and sick contacts. Wash gently, keep the skin cool and dry, wear loose clothing, and avoid scratching or applying several new creams at once. Do not stop a prescribed medicine without medical advice, but contact the prescriber promptly if the rash began after starting it.

Seek urgent help for rash with trouble breathing, swelling of the lips or tongue, faintness, severe illness, purple or bruise-like spots, skin peeling, blistering, or painful involvement of the eyes, mouth, or genitals. Arrange prompt review for fever, rapid spread, pus, significant pain, or a rash after a new medicine. A child, older adult, pregnant person, or person with reduced immunity may need earlier assessment.

What features point toward allergy, infection, irritation, or inflammation? Could a new medicine or product be responsible? Do I need testing or a skin examination? Which products are safe while it heals, and what change should trigger urgent care?