Heat rash (prickly heat): symptoms, treatment and how long it lasts

The NHS lists three main symptoms of heat rash: small, raised spots, an itchy or prickly feeling, and mild swelling. The spots are described as 2mm to 4mm across, and some of them may be filled with fluid.

The NHS says the symptoms are often the same in adults and children, and that the rash can appear anywhere on the body and spread. Patient, a UK patient information site, adds that it is commonly found in skin folds and in places where clothing rubs.

On white skin the rash looks red. The NHS says it may be harder to see, or look grey or white, on brown or black skin, so feel for the raised spots as well as looking for colour.

• Small, raised spots, often 2mm to 4mm across.

• An itchy, prickly feeling.

• Mild swelling of the affected skin.

• Some spots may be filled with fluid.

• Redness on white skin; grey or white spots may be seen on brown or black skin.

The NHS says that the main thing to do is keep your skin cool so you do not sweat and irritate the rash. Most people need nothing more than simple self-care, and Patient says that in most cases the rash will clear without any treatment.

To keep the skin cool, the NHS suggests wearing loose cotton clothing, using lightweight bedding, taking cool baths or showers and drinking plenty of fluid to avoid dehydration.

To calm the itching or prickly feeling, the NHS suggests applying something cold, such as a damp cloth or an ice pack wrapped in a tea towel, for up to 20 minutes. Tap or pat the rash instead of scratching it, and avoid perfumed shower gels or creams.

The NHS says a pharmacist can give advice and suggest the best treatment. It lists calamine lotion, antihistamine tablets and hydrocortisone cream as options a pharmacist might recommend, but hydrocortisone cream is not for children under 10 without advice from a doctor. Patient notes that hydrocortisone should not be used on the face and should be used sparingly.

The NHS says heat rash usually gets better on its own after a few days. It also explains that when sweat glands are blocked the trapped sweat leads to a rash developing a few days later, so the rash can appear after the sweating has happened.

Patient describes the common type (miliaria rubra) as tending to go within a few days if you get out of the hot environment and stop sweating. The least itchy type (miliaria crystallina) tends to disappear within a few hours or days, and it says severe cases can last for several weeks.

If the rash has not improved after a few days, the NHS advises seeing a GP. A rash that keeps coming back or does not settle is worth getting looked at because other skin conditions can look similar.

The NHS says heat rash is usually caused by sweating a lot. Sweat glands get blocked and the trapped sweat leads to a rash developing a few days later.

Patient explains the mechanism in more detail. Sweat is made in glands under the skin and travels up a duct to the surface. If the duct is blocked, sweat seeps into nearby skin and causes tiny pockets of inflammation. Anything that blocks the ducts can cause it, including tight clothing or bedding that is too warm.

It is not a sign of poor hygiene, and Patient says it is not an infection. It can happen in cool climates too: people who lie on their back for long periods during an illness may get it on the back, as may anyone wearing too many clothes or using bedding that is too warm.

The NHS says babies often get heat rash because they cannot control their temperature as well as adults and children can. Patient says it is most common in babies and children because their sweat glands are immature and more prone to blockage, and that it is particularly common in newborns but soon clears.

The NHS advises seeing a GP if your baby has a rash and you are worried. As a parent you know your child best. The NHS rashes guide says to call 999 or go to A&E if a child is unwell with a rash and has a stiff neck, is bothered by light, seems confused, has difficulty breathing, or has a rash that looks like small bruises or bleeding under the skin and does not fade when a glass is pressed against it.

It also says to ask for an urgent GP appointment or call NHS 111 if a child has a rash you are worried about and you are not sure what to do, or has a high temperature (38C if under 3 months old, 39C or higher if 3 months or older).

For hydrocortisone, the NHS says not to use it on children under 10 unless a doctor has advised it.

No. The NHS says heat rash can spread over your own body but cannot be passed on to other people, and Patient agrees that it is not contagious. If a rash comes with a temperature or your child seems unwell, use the urgent advice above rather than assuming it is heat rash.

Doctors call heat rash miliaria. Patient describes four types, depending on how deep in the skin the blockage sits. Most people have the common, itchy type that is usually called prickly heat.

Several common rashes are itchy or raised. The NHS rashes guide groups them by how they look and where they appear. The table below compares heat rash with the rashes it is most often confused with. If you are not sure, a pharmacist or GP can help.

Most heat rash is harmless, but hot weather can also cause heat exhaustion and heatstroke. The NHS lists the symptoms of heat exhaustion as tiredness, dizziness, headache, feeling or being sick, excessive sweating with pale, clammy skin, cramps, a high temperature, being very thirsty and feeling irritable.

The NHS says to cool the person down by moving them somewhere cool, removing unnecessary clothing, giving plenty of water to drink, cooling the skin with cool water and a fan, and staying with them. They should start to feel better within 30 minutes.

Call NHS 111 if you are struggling to treat the symptoms of heat exhaustion. Call 999 if there are signs of heatstroke, including still being unwell after 30 minutes of resting in a cool place, a very high temperature, hot skin that is not sweating, a fast heartbeat, fast breathing, confusion, a seizure or loss of consciousness.

Patient adds that if the rash covers a large part of the body you have a small risk of developing a fever or heat exhaustion, because you cannot sweat properly to get rid of body heat.

• See a GP if heat rash has not improved after a few days.

• See a GP if your baby has a rash and you are worried.

• Call NHS 111 if you are struggling to cool down someone with heat exhaustion.

• Call 999 if there are signs of heatstroke or a child with a rash has a stiff neck, breathing difficulty, confusion or a non-fading bruise-like rash.

Patient suggests sleeping in a cool, ventilated room, avoiding tight or excessive clothing, wearing cotton or breathable fabrics, removing wet clothing and taking a cool bath or using cool compresses if you get too hot.

The NHS heatwave guide advises keeping out of the heat, having cold food and drinks, keeping your living space cool by closing curtains in the day, and checking on people at higher risk, such as older people and babies and young children aged 5 and under. It says electric fans can help if the temperature is below 35 degrees.

Most heat rash is managed without any appointment. The NHS says a pharmacist can give advice and suggest the best treatment. If the rash does not settle, a GP can examine it and confirm the diagnosis. A dermatology appointment would usually follow a GP referral if the rash keeps coming back or the diagnosis is unclear.

Private dermatology appointments are also available if you prefer to arrange one yourself. The assessment is the same in principle: looking at the skin and asking about heat, clothing and sweating. For a baby, speak to your GP, health visitor or NHS 111 first.