Allergic Rash

Hives or contact dermatitis?

Timing is the most useful clue. Hives (urticaria) are raised, itchy pink or red welts that can appear anywhere and often fade within 24 hours. Triggers include insect stings, foods, medicines, infections and heat, and sometimes no cause is found. Allergic contact dermatitis is slower: it usually develops two or more days after skin contact with an allergen such as nickel, perfume, cosmetics or plants, starts where the skin touched it and may spread beyond. So think back several days, not just to today. If you are not sure the rash is allergic, start with rash; for itch without a visible rash, see itchy skin.

When hives are part of anaphylaxis

Hives and swelling of the lips, face or eyes are signs of a mild to moderate reaction, which can sometimes come before anaphylaxis. Treat it as anaphylaxis if there is difficult or noisy breathing, swelling of the tongue, swelling or tightness in the throat, wheeze or persistent cough, difficulty talking or a hoarse voice, persistent dizziness or collapse, a young child becomes pale and floppy, or, after an insect sting, tummy pain or vomiting. Use an adrenaline autoinjector immediately if one is available, then call Triple Zero (000), and follow an ASCIA action plan if there is one. Exercise, heat and alcohol can make allergic reactions more severe.

Sources: healthdirect — Hives (urticaria); ASCIA — Allergic contact dermatitis; healthdirect — Contact dermatitis; ASCIA — Anaphylaxis