Heat Rash: Signs, Self-Care and When to See a Pharmacist

Heat rash is a skin reaction to heat and sweat: small red spots or raised bumps that sting or prickle, usually on the face, chest, back and thighs. It happens when sweat glands are blocked because someone is sweating more than normal, and it is not serious. Once the skin cools and sweat can escape again, the rash should go in a few days¹.

What to do is simple. Move to a cooler place, take off unnecessary clothing, drink plenty of water, and cool the skin with a cool (not cold) shower or a spray of cool water. Do not use perfumed shower gels or creams, as these can irritate the skin further¹. If the itch is troublesome, a pharmacist can suggest calamine lotion, an antihistamine or a low strength hydrocortisone cream¹.

The important thing to rule out is heat illness. Heat rash is a rash; heat exhaustion is a whole-body illness with tiredness, weakness, feeling faint, headache, muscle cramps, feeling or being sick, heavy sweating and intense thirst². If someone feels unwell with a high temperature in hot weather, treat it as possible heat exhaustion and cool them down within 30 minutes³.

What heat rash looks like, and where it appears

Heat rash consists of small red spots or raised bumps that can cause a stinging or prickling feeling on the skin¹. The full set of signs is a rash of tiny red spots, blisters or bumps; a prickling or burning feeling on the skin; itchy skin; and redness with mild swelling¹. It can appear anywhere on the body, but usually turns up on the face, chest, back and thighs¹.

The cause is mechanical rather than infectious. It occurs when sweat glands are blocked because the person is sweating more than normal¹. Hot, humid weather, a warm bedroom, tight clothing or too many layers all keep sweat on the skin, and the glands that should carry it away become blocked. That is why the rash tends to appear in the places where clothing sits close or sweat collects.

Some medicines make sweating less effective, which raises the risk of heat problems generally. Guidance for Berkshire lists medications that interfere with sweating, such as anticholinergics or beta blockers, among the things that increase risk in hot weather⁶. If you take either and are struggling in the heat, speak to your pharmacist or doctor rather than stopping anything yourself⁷.

It helps to know what heat rash is not. A rash that starts as tiny red or pin-prick spots and develops into larger red or purple blotches that look like bruises is not heat rash: that is the rash associated with septicaemia, caused by blood leaking into the tissues under the skin, and it needs urgent assessment⁸. A measles rash is different again: it usually appears 2 to 4 days after cold-like symptoms started, beginning on the face and behind the ears before spreading⁹.

Self-care at home: cool the skin, drink water, skip the perfume

The aim of self-care is to stop the sweating that blocked the glands and let the skin settle. Official heat illness advice is to move to a cooler place, remove unnecessary clothing or accessories, drink fluids such as water or a rehydration drink, and apply cool water to exposed skin using a spray or sponge while fanning the person quickly¹⁰. For heat rash specifically, tell them to drink lots of water to prevent them becoming dehydrated¹.

Cooling the skin directly is the main treatment:

• Take cool (not cold) baths or showers, and splash yourself with cool water¹¹.
• Fill spray bottles with cool water to use on your face and body¹².
• Sprinkle water over the skin or clothing, or keep a damp cloth on the back of your neck¹³.
• Have plenty of cold drinks, and avoid excess alcohol, caffeine and hot drinks¹³.
• Eat cold foods, particularly salads and fruit with a high water content¹³.

Clothing and bedding matter as much as washing. Loose, light layers let sweat escape; tight waistbands, synthetic fabrics and heavy duvets trap it. If the itch is worse at night, the cause is usually a warm bedroom, so cooling the room before bed and using lighter bedding does more than scratching. There is more on this in our guide to how to sleep and cool a bedroom on hot nights.

Keep an eye on how much everyone is drinking in the heat. Our page on how much water to drink in hot weather sets out what to aim for, and dehydration in hot weather explains the signs to watch for, particularly in children.

Heat rash is not serious, and should go in a few days

If someone has these symptoms, the rash is not serious and should go in a few days¹. That is the reassuring headline: heat rash is uncomfortable rather than dangerous, and it resolves once the skin cools and the sweat glands clear.

It helps to put that timescale beside other hot weather skin and heat problems, so you know what to expect and when to ask for help:

If the rash has not settled after several days, or it is spreading, weeping, or hot and painful to touch, that is no longer the simple picture and is worth a conversation with a pharmacist or GP. Equally, a rash with a high temperature, drowsiness or confusion is not heat rash and should be treated as possible heat illness.

When to see a pharmacist, and what they can offer

A pharmacist is the right first stop for an itchy heat rash that is not settling. They may prescribe calamine lotion, an antihistamine, or low strength hydrocortisone cream¹. Calamine lotion can help soothe itching, irritated skin, rashes and sunburn, and gels and mousses are also available for some rashes¹⁷.

If you are worried about someone else's health, contact your local pharmacist, your GP or NHS 111, who will all be able to help⁵. If your medicines seem to work differently during hot weather, speak to your pharmacist or doctor⁷. If you have any concerns about your medication in hot weather, speak to your pharmacist or healthcare professional¹⁸.

Heat rash or heat exhaustion? How to tell the difference

This is the distinction that matters most, because one is a nuisance and the other can become an emergency. Heat rash is a skin rash. Heat exhaustion is when the temperature inside the body rises to 37 to 40C or above¹⁵, and it can develop quickly over a few minutes, or gradually over several hours or days¹⁹.

The symptoms of heat exhaustion are tiredness, weakness, feeling faint, headache, muscle cramps, feeling or being sick, heavy sweating and intense thirst². The symptoms are often the same in adults and children, although children may become irritable too²⁰. Heat exhaustion can come on gradually or suddenly²⁰.

If you or someone else feels unwell with a high temperature during hot weather, it may be heat exhaustion or heatstroke³. Heat exhaustion does not usually need emergency medical help if you can cool down within 30 minutes, but call 999 if you suspect it has turned into heatstroke¹⁶. Dehydration leading to heat exhaustion or heatstroke requires urgent treatment²¹, and heat exhaustion or heatstroke can develop quickly over a few minutes, or gradually over several hours or days¹⁹.

Our guide to heat exhaustion and heatstroke sets out the full signs and what to do, and when to call 999 or NHS 111 for heat illness covers the decision in detail. If you are checking on someone else, our page on who is most at risk in hot weather explains why older people, babies and people on certain medicines need closer watching.

Babies and young children: the same rash, a closer eye

Heat rash in a baby looks the same as in an adult, and the self-care is the same: cool the skin, keep them lightly dressed, and avoid perfumed products¹. What differs is the margin for error. Babies and young children can be seriously affected in very hot weather by dehydration, heat exhaustion and heatstroke, and sunburn²².

Overheating in babies has its own causes: too much bedding or clothing, or a room that is too hot²³. Dress a baby in light layers, use lighter bedding in hot weather, and check the back of the neck rather than the hands to judge temperature. Our guide to keeping babies and young children safe in hot weather goes through this in detail, and the baby and child hot weather checklist is a practical list to work from.

Watch for the signs that this is more than a rash. A child who develops a rash, itchiness or swelling on their hands, feet or face, whose breathing may slow down, or who vomits or has diarrhoea, may be having a severe allergic reaction and needs urgent help²⁴. A child who is drowsy, irritable, has a high temperature or is not drinking is also a reason to seek advice rather than wait.

Preventing heat rash during a heatwave

Prevention is the same cooling advice, applied before the rash appears. If a heat wave is forecast, plan your day to stay out of the heat, and avoid going out in the hottest part of the day, between 11am and 3pm²¹. Cover up in the sun, limit time outside, particularly in the middle of the day, and drink plenty of water to remain hydrated¹⁸.

Before a hot spell, check that fridges, freezers, fans and air-conditioners are working properly¹². Fill spray bottles with cool water to use on your face and body¹². Have appropriate sun cream for your particular type of skin²¹. And keep the home itself cooler where you can: our guide to keeping your home cool in hot weather covers shading windows, ventilation and when to open and close them.

A few habits make a difference day to day:

• Wear loose, light clothing so sweat can escape, and change out of damp clothes.
• Shower cool rather than hot, and pat the skin dry rather than rubbing.
• Avoid perfumed shower gels and creams¹.
• Keep bedrooms cooler before bedtime, and use lighter bedding.

If you take medicines that interfere with sweating, such as anticholinergics or beta blockers, plan ahead with your pharmacist or doctor⁶. Our page on medicines that raise the risk of illness in the heat explains more, and the hot weather preparation checklist is a full list to work through before a heatwave arrives.