Allergic skin reactions usually come on relatively quickly after exposure to a trigger. Hives (urticaria) are raised, itchy welts that can move around the body and fade within hours, while contact dermatitis appears where skin touched something irritating or allergenic, such as nickel jewellery, cosmetics, latex or certain plants.
Clues that a rash is allergic include a clear timing link to a new food, medicine, detergent or product, intense itch, and improvement when you stop the exposure. A rash that follows starting a new medication should always be discussed with a doctor or pharmacist, as some drug reactions can become serious.
Treat any rash with lip, tongue, face or throat swelling, wheezing, difficulty breathing or faintness as a possible severe allergic reaction and seek emergency care immediately. For milder, persistent or recurring rashes, a clinician can help identify the trigger and advise on suitable over-the-counter or prescription options. This is general guidance, not a diagnosis.