Allergy rash: how to recognise and respond to it

Timing offers useful clues. A rash after skin contact with a new product may fit contact dermatitis, while rapidly appearing welts that shift location can resemble hives. Infection, heat, eczema, scabies, psoriasis, and medicine reactions can produce overlapping features.

Look at the shape, location, sensation, and pace of change. Contact reactions often stay where a substance touched the body; eczema may produce dry, cracked, intensely itchy patches; ring-shaped scaly areas can have another cause. A drug rash may be widespread and can start after a medicine that was recently begun or adjusted.

Skin colour changes how inflammation looks. On lighter skin it may appear pink or red; on darker skin it may look purple, grey, deep brown, or simply darker than nearby skin. Warmth, swelling, texture, and tenderness are important clues too.

Stop non-essential new cosmetics, fragrances, and topical products that may have touched the area. Rinse away a suspected contact substance, apply a cool compress, choose loose clothing, and moisturise with a simple fragrance-free product. Scratching can break the skin, so keep nails short and use gentle pressure instead.

A pharmacist can advise whether an antihistamine or topical treatment suits your symptoms, age, pregnancy status, health conditions, and other medicines. Photograph the rash and record foods, medicines, products, work exposures, travel, and whether anyone nearby is itchy.

Get emergency help for breathing difficulty, wheezing, faintness, throat tightness, or swelling of the lips, tongue, or face. Urgent assessment is needed for blistering or peeling, severe skin pain, fever, purple spots that do not fade with pressure, or involvement of the eyes, mouth, or genitals.

Contact a clinician promptly when the rash follows a new medicine, spreads quickly, shows pus or increasing warmth, repeatedly returns, or does not settle after the suspected trigger is removed.

Ask which diagnoses fit the distribution, whether testing would change management, and which treatments are safe for the affected area. Clarify how long to avoid a suspected product, whether a medicine needs an alternative, and what recurrence plan to follow.