Heat Rash (Prickly Heat): Causes, Treatment and Prevention

What causes heat rash?

When the body sweats heavily in hot, humid weather, sweat may not reach the skin surface easily. The openings of the sweat glands become blocked and sweat leaks into the nearby layers of skin, causing irritation and a rash.

This blockage is more likely with tight or synthetic clothing, heavy bedding, thick greasy creams and ointments, lying in bed for long periods with a fever, or exercising in the heat. That is why heat rash is common in the humid summer months and in babies, whose sweat glands are not yet fully developed.

What types are there and what do they look like?

The rash looks different depending on how deep in the skin the sweat duct is blocked:

• Superficial type: tiny clear blisters like water droplets that burst easily and usually do not itch; common in newborns.
• Red type, or prickly heat: small red bumps with intense itching or prickling that worsens with sweating; the most common type in adults.
• Deep type: slightly larger skin-coloured bumps that appear after repeated episodes; less common, and it may reduce sweating in the area.
• Usual locations: the neck, upper chest and back, under the breasts, armpits, elbow creases and thighs.

How can I ease it at home?

The most important step is to move the skin away from heat and let the sweat escape. Mild heat rash usually improves within a few days with these steps:

• Move to a cool, air-conditioned or well-ventilated place.
• Take a lukewarm to cool shower and pat the skin dry rather than rubbing.
• Wear loose cotton clothing, or leave the area uncovered when possible.
• Avoid heavy, greasy creams and ointments on the area, as they increase blockage.
• Calamine lotion or cool compresses may ease the itching.
• Do not scratch the bumps, as scratching can break the skin and lead to bacterial infection.

Heat rash in babies and children

Babies are more prone to this rash, and the usual cause is being dressed too warmly; some parents wrap babies in several layers even in hot weather or under weak air-conditioning. A baby usually needs only one more layer than an adult would wear in the same conditions.

Dress your child in light cotton clothes, keep the room at a moderate temperature and avoid putting oils or heavy creams on the rash. Watch for warning signs: if a baby under 3 months has a temperature of 38°C or higher, seems unusually sleepy or is feeding poorly, or the rash spreads with a fever, see a doctor straight away, because fever at this age needs urgent assessment whatever the cause of the rash.

When is a rash not heat rash?

Many rashes look alike, and what seems to be heat rash may in fact be inflamed hair follicles, a fungal infection in the skin folds, an allergy to a product or fabric, or a viral rash. So if the rash does not improve after 3–4 days of cooling and ventilation, or looks different, it is best to have a doctor see it.

A doctor may prescribe a suitable topical treatment for severe itching or inflammation. Do not apply cortisone or antibiotic creams on your own, especially on a child's face or in skin folds, because using them in the wrong place can hide the real problem or make it worse.