Heat Rash

Overview

Heat rash (also called prickly heat or miliaria) is a red, itchy or prickly skin irritation that happens when sweat gets trapped under the skin. Tiny sweat ducts can get blocked when you sweat a lot, so sweat builds up underneath and forms little bumps. It is not contagious and it is not usually serious. Most of the time it settles on its own once your skin cools down and dries off.

Yes, heat rash is very common. It can affect anyone, but it is especially common in babies and young children, and in adults living in hot, humid weather.

Babies and young children are affected most often because their sweat ducts are still small and develop. It also affects adults who work or exercise in the heat, people who wear tight or non-breathable clothing, people who are on bed rest or have a fever, and people who are overweight, because sweat can get trapped in skin folds.

Symptoms

Common symptoms

• Tiny red, clear or skin-coloured bumps, often in clusters
• A prickling, stinging or itchy feeling, which is why it is called prickly heat
• Redness or mild swelling in the affected area
• Patches in skin creases such as the neck, armpits, elbow creases, groin and under the breasts
• Bumps under tight clothing, straps, or where a nappy or dressing sits
• Symptoms that get worse in hot, humid weather or after sweating and ease when the skin cools

Symptoms in children

• Clusters of tiny bumps on the neck, chest, back, shoulders and in the nappy area
• Fussiness or irritability, especially in warm rooms or when overdressed
• Restlessness and poor sleep in hot weather because of the prickling feeling
• Rubbing or scratching at the area
• Bumps that look worse after being wrapped up or after a feed in a warm room

Symptoms in older adults

• Rash in skin folds, under the breasts, in the groin, or under medical dressings and pads
• Rash in areas where a person lies or sits for long periods, especially if they cannot move easily
• Itch that may be less obvious, so the rash is noticed before the discomfort
• Skin that looks red, moist or irritated in creases
• In people who feel cold and are wrapped up warmly, sweat can still get trapped and cause a rash

Causes

Main causes

• Blocked sweat ducts: when you sweat a lot, the tiny openings of the sweat glands on the skin can get blocked, so sweat leaks into the skin and causes bumps
• Hot, humid weather, which makes sweating heavier and stops sweat from evaporating quickly
• Wearing clothing that does not breathe well or that fits tightly, trapping sweat against the skin
• Being wrapped up too warmly, especially babies and young children
• Sitting or lying in the same position for a long time, so sweat collects in skin folds
• Using heavy creams or ointments that block the skin's pores

Risk factors

• Being a baby or young child, because sweat ducts are still developing
• Living in or visiting a hot, humid climate
• Doing physical work or exercise in the heat
• Being overweight, which increases sweating and skin folds
• Being on bed rest, using a wheelchair, or having limited movement
• A recent fever or illness that makes you sweat
• Wearing tight uniforms, sports kit, or protective equipment for long periods
• Taking medicines that make you sweat more — ask your doctor or pharmacist if you are unsure

When to see a doctor

See a doctor urgently if:

• Redness that is spreading quickly, or the area becomes hot, swollen and painful
• Pus, weeping, or an unpleasant smell from the rash
• Fever with a rash, or a rash that does not fade when pressed with a glass
• A baby under 3 months old with a fever or a rash you are worried about
• Signs of heat exhaustion, such as feeling dizzy, sick, having a headache, or feeling very tired in hot weather

Book a routine appointment if:

• The rash has not settled after several days of keeping the skin cool and dry
• It keeps coming back and is affecting work, sleep or daily life
• You are not sure what the rash is
• The itch is very bothersome despite simple cooling measures
• Your child seems uncomfortable or is scratching enough to break the skin

Diagnosis

A doctor or pharmacist can usually tell it is heat rash just by looking at your skin and asking a few questions, like where the rash is, how long you have had it, and whether you have been hot or sweating a lot. No special tests are normally needed.

Tests that may be done

• Usually none — the diagnosis is based on how the rash looks and your recent history
• Occasionally a swab from the skin if the doctor thinks it might be infected
• Rarely, a referral to a skin specialist (dermatologist) if the rash keeps coming back or the cause is unclear

What to expect at your appointment

The appointment is quick and simple. You may be asked to show the rash, so wear clothing that is easy to remove or lift. Your doctor will check whether the rash looks like heat rash or something else, such as a skin infection, eczema, or a reaction to a product. You will usually be given advice on cooling the skin and keeping it dry, and told what to look out for.

Treatment

The main treatment for heat rash is cooling and drying the skin. In most cases that is all that is needed, and the rash fades within a few days. Medicines are rarely needed and are only used if the skin becomes infected or the itch is very troublesome.

Self-care at home

• Move to a cool, shaded or air-conditioned place, or use a fan to cool the room
• Take off tight clothing and change into loose, light, cotton clothing
• Gently pat the skin dry — do not rub — and let the area get some air
• Have a cool shower or bath, or gently sponge the area with cool water, then pat dry
• Keep the affected skin uncovered where possible so it can breathe
• Avoid heavy creams, oils and ointments on the area, as these can block sweat ducts further
• Drink plenty of water so you stay hydrated in the heat
• Keep your child cool and avoid over-wrapping — check their neck to see if they are too warm
• Try not to scratch; keep nails short and consider cotton mitts for babies at night
• Ask your pharmacist about soothing preparations suitable for your age, including for babies

Medical treatments

Most heat rash does not need prescription treatment. If the skin is itchy or inflamed, your doctor or pharmacist may suggest a soothing lotion or a mild anti-inflammatory cream, and if there are signs of infection they may prescribe an antibiotic cream or, in some cases, antibiotic tablets. Your doctor will choose what is suitable for your age, whether you are pregnant, and any other conditions you have. Always check with a pharmacist before using any cream on a baby's skin.

When is surgery considered?

Surgery is not used to treat heat rash.

Living with this condition

Heat rash usually settles quickly, but on hot days it can come and go. The key is to keep your skin cool and dry. Loose cotton clothes, a fan, cool showers and avoiding heavy creams will help most days. If you know a heatwave is coming, plan ahead — keep rooms shaded, drink regularly, and take breaks in the cool.

Lifestyle tips

• Wear loose, light-coloured, breathable fabrics such as cotton
• Change out of sweaty clothes and sportswear promptly after exercise
• Shower or bathe regularly in hot weather to keep skin clean and free of sweat
• Use lightweight bedding and avoid thick duvets in summer
• Take breaks in the shade or in a cool room when working or exercising outdoors
• Keep babies and young children in light layers and check them often
• If you are on bed rest, change position regularly and keep skin folds clean and dry

Diet and exercise

There is no special diet for heat rash, but drinking water regularly helps your body manage heat. When it is hot, exercise earlier in the morning or later in the evening, choose cooler indoor spaces, and take more breaks than usual. Wash and dry sweaty skin after exercise. If you have a health condition or take medicines that affect sweating or hydration, ask your doctor for advice on exercising in the heat.

Mental health and emotional wellbeing

An itchy rash can be irritating and can disturb sleep, especially for parents of young children who are up in the night. This can leave you feeling tired and short-tempered. Try to remind yourself that heat rash is common, not harmful, and usually short-lived. If worry about the rash or ongoing sleep problems are affecting your mood or your child's wellbeing, speak to your doctor or health visitor — support is available.

Prevention

Yes, heat rash can often be prevented, or at least made much less likely, by keeping the skin cool and dry in hot weather.

Screening programmes

There is no screening test for heat rash. It is a skin problem you notice yourself, and it is diagnosed by looking at the skin.

Complications

If left untreated

• Most heat rash clears up on its own without any problems
• Scratching can break the skin and let bacteria in, which can lead to a skin infection
• A skin infection can spread and may need antibiotic treatment
• Heat rash that keeps coming back can be uncomfortable and disturb sleep
• Rarely, repeated heat rash in the same area can cause small hard bumps or altered skin colour, which usually fades with time

Long-term outlook

The outlook is very good. Heat rash is common, harmless in most people, and usually settles within a few days once the skin cools. With small changes like cooler rooms, looser clothing and regular drinks, most people find it is easy to manage, and it does not cause lasting harm to the skin.

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