Heat rash – sometimes called prickly heat, sweat rash or miliaria – is a common and uncomfortable condition. It’s an itchy rash that can happen when you overheat and start to sweat a lot. You get tiny, red raised bumps or spots that cause a prickling or stinging feeling.
Wearing too many clothes, exercising, or just being in hot and humid conditions can mean your sweat glands get blocked. When this happens, the sweat gets trapped instead of evaporating on your skin’s surface. The skin around your sweat pores then gets itchy, red and irritated.
Heat rash is usually nothing to worry about. But it can make summer hard work. “It may stop you from being active outdoors and can disrupt your sleep. And you might feel self-conscious about how the rash looks in summer clothes,” says Dr Adiele Hoffman, doctor and Healthily expert.
So don’t put up with it - there are things you can do to beat the rash. Here’s what you need to know about common symptoms and causes of heat rash – and how to deal with it.
Who gets heat rash?
Heat rash can affect anyone in humid and warm conditions – whatever your age or gender. It isn’t infectious so you can’t spread it to anyone else, or catch it from someone. And it isn’t caused by not washing your skin well enough or by being “dirty”.
Babies and young children tend to get prickly heat rash more often. This is likely to be because it’s harder for them to regulate their body temperature as their sweat glands aren’t yet fully developed. Research suggests heat rash affects between 4.5% and 9% of newborn babies.
As an adult, you’re more likely to get heat rash if you:
- live in a warm climate – it affects as many as 30% of adults living in hot, humid and sweaty conditions
- sweat excessively
- have a fever during an illness
- are physically active
- have mobility issues or have to stay in bed a lot
- wear close-fitting, non-breathable clothes – like leggings, tight trousers or tights – which stop sweat evaporating and don’t allow enough airflow between your skin and your clothing
There are also some conditions and treatments that are linked with heat rash, such as radiotherapy and induction chemotherapy (the type you might have as the first part of your treatment, before surgery or radiotherapy).
What are the symptoms of heat rash?
The main symptoms include:
- small, raised red spots or small blisters
- a prickly, itchy feeling on your skin
- mild swelling
- a red rash that can appear anywhere on your body. This rash may appear less obvious on brown or black skin
Where does heat rash show up?
- young children’s heat rash most often appears around their neck, armpits and groin, where their skin creases and sweat collects
- as an adult, you’re likely to get heat rash in the folds of your skin, or in areas covered by clothing that makes you sweat, irritating the skin
Worried about your symptoms but not sure if you need to see a doctor? You can try our Smart Symptom Checker to help you work out your best next steps. But if you’re worried, don’t be afraid to go to the doctor (see When to see a doctor about heat rash.
Other conditions that often get mistaken for heat rash are:
- polymorphic light eruption – this skin rash can look similar but it’s triggered by sunlight or artificial UV light rather than heat
- eczema – warm weather can worsen eczema in children, especially in areas where moisture gathers, like the insides of the elbows, around the neck and back of the knees
Self-care tips for dealing with heat rash at home
There are lots of simple self-help measures you can try at home.
Help prevent heat rash
- keep out of heat and humidity if you can – if you’re outdoors, stay in the shade and take a small fan with you
- use a fan or air conditioner (but never blow a fan directly on a baby)
- wear cool, loose cotton clothing – synthetic fibres, like nylon and polyester, can trap heat and make you sweat more than natural fibres like cotton
- choose lightweight bedding to avoid overheating and sweating during the night
- have cool baths or showers – make sure your skin is completely dry before you put your clothes on
Soothe your heat rash
- tap the rash dry after a bath or shower, instead of rubbing or scratching it
- avoid perfumed bubble baths, shower gels or creams as they can irritate your skin more. Step away from baby powders, ointments and any lotions containing petroleum – these can all clog your pores and make the rash worse
- apply a damp cloth or an ice pack wrapped in a tea towel to the rash for up to 20 minutes
- add colloidal oatmeal to a lukewarm bath. We’re not talking breakfast oats here. It’s a finely ground oat powder, available in sachets from pharmacies, which dissolves easily in water and can help soothe and heal inflamed skin. Or you can buy standard oats from the supermarket and whiz them into a fine powder that turns into a milky-white liquid when added to water
- if your baby has a rash near or in their nappy area, leave them nappy-free for a few hours, or loosen the nappy
How can a pharmacist help with heat rash?
If self-care measures haven't helped soothe your rash, a pharmacist may recommend:
- calamine lotion – this can help calm sore and irritated skin. It can be drying so you might need to moisturise your skin as well. The pharmacist can recommend one that won’t block pores
- hydrocortisone cream – you can get low-strength hydrocortisone cream from pharmacies and it can help ease irritated and itchy areas of skin. It’s not suitable for children under 10 or if you’re pregnant
- antihistamine tablets – these can help to relieve the itching and swelling
- paracetamol – to help reduce a fever if that’s the cause of your heat rash
When to see a doctor about heat rash
Heat rash is usually harmless but if your rash hasn’t improved after a few days, make an appointment with a doctor. And if you have any concerns about a rash your baby has, don’t hesitate to speak to a doctor.
It’s also important to get medical help if you have any severe symptoms accompanied by heat rash, including:
- itching that feels severe
- your rash starts to leak pus or fluid or you experience nausea, swelling or fever. This may be a sign of infection
Call an ambulance or go to the emergency department if you have a rash that doesn’t disappear when you press a glass to it.
How is heat rash diagnosed?
A doctor will be able to diagnose heat rash by examining your skin.
How is heat rash treated?
Heat rash normally goes away without any treatment. The self-care measures above should help ease your symptoms.
If your heat rash has become infected, your doctor may advise antibiotics.
Tip from a doctor
“To quickly ease your heat rash, you need to stop sweating. Ideally, move to a cooler place, whether that’s the shade or inside. Take off any tight clothing and have a cool shower. If that’s not possible, you could grab a cold compress to soothe your skin.”