Heat Rash and Prickly Heat: Care and Prevention

What heat rash is

Heat rash, often called prickly heat, happens when the tiny ducts that carry sweat to the skin surface become blocked or inflamed. The sweat is trapped under the skin, and a rash appears a few days later. It is uncomfortable but usually harmless. It is common in hot, humid weather, during heavy physical work or exercise, and in people who spend long periods in bed with a fever.

What it looks and feels like

Heat rash shows as small, raised spots, usually 2mm to 4mm across. Some spots may be filled with fluid. There is often an itchy, prickly feeling and mild swelling. On white skin the rash looks red. On brown or black skin it may be harder to see, or look grey or white, so feel for the bumpy texture as well as looking.

In adults it usually appears in skin folds and where clothing rubs. In babies it tends to show on the neck, shoulders and chest, and also in the armpits and groin. Doctors describe different types depending on how deep the blockage is, from clear, easily broken blisters to deeper, firm and painful bumps. If the bumps fill with pus, that is a sign the skin may be infected.

How to care for it at home

1. Move to a cooler, well-ventilated place and rest from heavy activity.
2. Wear loose cotton clothing and use lightweight bedding.
3. Take cool baths or showers.
4. Hold something cool, such as a damp cloth, on the rash for up to 20 minutes.
5. Tap or pat the rash gently instead of scratching it.
6. Drink plenty of fluid so you do not become dehydrated.

A pharmacist can suggest a soothing lotion or cream for itching. Ask before using any cream on a young child, as some are not suitable for children.

What not to do

• Do not scratch the rash. Broken skin lets bacteria in and can lead to infection.
• Do not use perfumed shower gels or creams on the affected skin.
• Do not use thick, greasy creams that can block the sweat ducts further.
• Do not wrap a baby in extra layers or heavy bedding because the rash looks sore.
• Do not keep working or exercising in the heat and hope the rash clears anyway.

How to prevent it

Prevention is mostly about sweating less and letting sweat escape. Wear loose, light clothing that moves moisture away from the skin. Limit activity during the hottest hours. Use a fan, or air conditioning if you have it, and keep sleeping areas cool and airy. Dry skin folds carefully after washing. For babies, dress them in one light layer, change nappies often and keep the cot away from direct sun.

When to get emergency help

Heat rash itself is not an emergency, but overheating can be. call Rescue 1122 where available, or go to the nearest hospital emergency department if the person has a very high temperature with hot skin that is not sweating, a fast heartbeat, fast breathing or shortness of breath, confusion or poor coordination, a seizure, or loss of consciousness. The same applies if someone with heat exhaustion is still unwell after 30 minutes of resting in a cool place.

See a doctor, rather than waiting it out, if the rash has not improved after a few days or is getting worse, if the spots become painful, warm, swollen or filled with pus, if there is a fever, or if a baby develops a rash. Do not delay medical advice because you think the rash is only a heat problem.