Heat rash or urticaria: what to know

Heat Rash, or miliaria, develops when sweat ducts become blocked in hot, damp conditions. It often appears as many small prickly bumps in an area covered by clothing or a skin fold. Urticaria, also called hives, produces raised welts that can change shape or move; warmth, exercise, pressure or another trigger may bring it on.

A Skin Rash, Skin Bumps or Skin Redness page can help with description, but examination may be needed when the pattern is unclear. A rash staying in the same place with scaling or moisture is less typical of fleeting hives and deserves a different assessment.

For suspected heat rash, cool the skin, reduce sweating, wear loose breathable clothing and keep the area dry. Wash gently and pat rather than scrub. For possible hives, avoid the suspected heat or pressure trigger and do not scratch. Record when each mark appears, how long it lasts and whether it leaves scaling or colour change.

Avoid experimenting with multiple creams at once. Emollient Therapy may help dry, friction-prone skin, but it will not treat every cause of a rash. Ask a clinician or pharmacist about suitable treatment before using Topical Corticosteroids when the diagnosis is uncertain.

Get emergency help if hives or swelling affect the lips, tongue or throat, or if breathing, swallowing, voice or alertness changes. Seek prompt medical care for rapidly spreading painful redness, fever, pus, marked swelling or feeling very unwell. Arrange assessment when the rash keeps returning, lasts unusually long in one place or does not respond to cooling.

Do the marks fit heat rash, urticaria or another condition? Could exercise, pressure, heat, a medicine or a product be triggering them? What should I record during an episode? Which symptoms require emergency help?