Heat Rash Prickly Heat

Overview

Heat rash — also called prickly heat — is a harmless skin irritation made up of tiny red or clear bumps. It happens when sweat gets trapped under the skin because the tiny tubes that carry sweat to the surface (sweat ducts) get blocked. The trapped sweat causes little spots that often itch, prickle or sting. It can appear anywhere, but it is most common in skin folds such as the neck, armpits, groin, under the breasts and in the bends of the elbows and knees. In babies it often shows up on the neck, chest, back and in nappy areas. Heat rash is not contagious and it does not spread from person to person.

Yes, heat rash is very common. It is one of the most frequent skin complaints in warm, humid weather and is especially common in babies and young children.

Anyone can get heat rash, but it is most common in babies and young children because their sweat ducts are small and narrow. It also affects adults who work or exercise in hot conditions, people who are overweight, people who sweat heavily, and people who are confined to bed or unable to move easily. It can also appear in people with a fever, or in anyone wrapped up too warmly.

Symptoms

Common symptoms

• Tiny red, pink or clear bumps, usually in clusters
• An itchy, prickly or stinging feeling in the affected area
• Small, slightly raised spots that look like little blisters or beads of moisture
• Mild swelling or tenderness around the spots
• Mild discomfort or a crawling feeling on the skin, especially when hot or sweating
• Slightly dry or rough-feeling skin once the bumps settle

Symptoms in children

• A patch of tiny red spots in the neck folds, armpits, chest, back or nappy area
• Fussiness, crying or rubbing at the skin because it itches
• Trouble settling to sleep in warm weather or when overdressed
• Clear little blisters that can look like tiny water drops on the skin
• Slightly reduced appetite or irritability during hot weather

Symptoms in older adults

• Rash in skin folds, under clothing or under the breasts, where sweat collects
• Spots under a dressing, plaster or in areas covered by bedding
• Rash in people who are immobile or lying in bed for long periods
• Less obvious itching than in younger people, so the rash may be noticed before it is felt
• Skin that looks damp or feels clammy in the affected area

Causes

Main causes

• Blocked sweat ducts: sweat cannot reach the skin surface and gets trapped, causing tiny spots
• Hot, humid weather, when sweating is heavy and sweat evaporates slowly
• Being wrapped or dressed too warmly, especially in babies
• Tight-fitting clothing or synthetic fabrics that trap heat and moisture
• Heavy physical activity or working in a hot environment
• Thick creams, ointments or heavy moisturisers that block sweat ducts
• A fever, or lying in bed for long periods under bedding

Risk factors

• Being a baby or young child, because sweat ducts are still very small
• Being overweight, as sweat collects in skin folds
• Living or working in a hot, humid climate
• Being immobile, unwell or bed-bound
• Wearing tight or non-breathable clothing
• Taking part in sports or doing heavy manual work in hot weather
• Having a fever or an illness that makes you sweat a lot

When to see a doctor

See a doctor urgently if:

• Any baby under 3 months with a rash and a temperature of 38C or higher
• Rash that becomes very painful, develops pus, or has spreading redness and warmth
• A child who is drowsy, floppy, not feeding well, or hard to wake
• A rash that does not fade when a glass is pressed against it, together with a fever
• Signs of heat exhaustion that do not improve after resting in a cool place and drinking fluids
• Signs of dehydration — dry mouth, sunken eyes, or very little urine

Book a routine appointment if:

• Heat rash that has not cleared after about a week of keeping the skin cool and dry
• Rash that keeps coming back in the same area
• Itching that is disturbing sleep or daily life
• You are unsure whether it is heat rash or something else
• The rash is in an area covered by a dressing, plaster or medical device

Diagnosis

A doctor or nurse can usually tell it is heat rash just by looking at your skin and asking a few questions, such as where the rash appeared, how long it has been there, whether you have been in hot weather, and whether it itches or hurts. There are no needles or machines involved. They will check whether the spots look like typical heat rash — small, even bumps in areas where sweat collects — and whether anything else might explain the rash, such as an infection or an allergic reaction.

Tests that may be done

• Usually none — the diagnosis is based on how the rash looks and your recent history
• In unusual or persistent cases, a doctor may look at a tiny skin sample under a microscope
• A skin swab may be taken if the area looks infected
• A temperature check if you or your child also have a fever

What to expect at your appointment

The appointment is quick and gentle. You will be asked to show the rash, and the doctor may gently press on the skin. You may be asked about hot weather, clothing, exercise, travel and any medicines or creams you use. Most people leave with simple self-care advice and reassurance, and no follow-up is needed. If the rash looks infected, you will be told what to look out for and when to come back.

Treatment

The main treatment for heat rash is simply to cool the skin and keep it dry. Most cases settle within a few days without any medicines. The aim is to unblock the sweat ducts, stop further sweating in that area, and prevent the skin from becoming infected.

Self-care at home

• Move to a cool, shaded or air-conditioned place and avoid the hottest part of the day
• Wear loose, light cotton clothing and avoid tight waistbands, straps and synthetic fabrics
• Take a cool (not freezing) shower or bath, then pat the skin dry gently rather than rubbing
• Let the skin air dry — avoid thick creams, ointments and heavy moisturisers on the rash
• Use a fan or a cool damp cloth on the skin to help it settle
• Drink plenty of fluids to stay hydrated and help your body cope with the heat
• Keep babies and children in loose clothing and avoid extra blankets; check them often in warm rooms
• Change out of sweaty clothes promptly after exercise and shower when you can
• Ask your pharmacist about simple cooling preparations suitable for your age — and mention if you are pregnant, breastfeeding or treating a young child
• Try not to scratch; keeping nails short helps, especially for children

Medical treatments

Heat rash usually clears without medical treatment. If the skin looks infected, or if the itching is severe and disturbing sleep, your doctor may suggest a treatment — this could be a medicated cream, an antiseptic preparation, or in some cases a short course of tablets. Your doctor or pharmacist will choose what is suitable for your age and situation and will explain how to use it. Never use a cream left over from a previous skin problem without checking first, because some products can block sweat ducts and make heat rash worse.

When is surgery considered?

Surgery is not used to treat heat rash.

Living with this condition

Heat rash usually lasts only a few days, but it can keep coming back if you stay hot and sweaty. The trick is to build small cooling habits into your day: check the weather before you dress, keep a change of light clothing handy, and take breaks in the shade when you are outdoors. For babies, check them regularly and dress them in roughly the number of layers you would wear yourself, plus one light layer at most.

Lifestyle tips

• Choose natural, breathable fabrics such as cotton and linen
• Keep rooms ventilated and use a fan or air conditioning in hot weather
• Shower after exercise and dry skin folds carefully
• Avoid sitting or lying in the same position for long periods if you are less mobile — change position often
• Use light bedding in summer and avoid plastic mattress covers next to the skin
• Keep a cool, damp cloth in a bag or freezer pack when travelling in hot places
• Choose gentle, unperfumed skin products and avoid thick barrier creams on sweaty areas

Diet and exercise

There is no special diet for heat rash, but drinking water regularly through the day helps your body manage heat. If you exercise in hot weather, choose cooler times such as early morning or evening, wear loose breathable kit, take breaks, and shower and change as soon as you can afterwards. If you are prone to heat rash, water-based activities such as swimming are a comfortable way to stay active in the heat. Speak to a doctor before starting a new exercise plan if you have a heart or lung condition or take medicines that affect sweating.

Mental health and emotional wellbeing

Heat rash is harmless, but constant itching and broken sleep can make anyone feel irritable and worn out, and it can be upsetting to see spots on your child. Parents often worry that they have dressed their baby wrongly — this is very common and it is not your fault. The discomfort is usually short-lived, and knowing it settles quickly can help you feel calmer. If worry, low mood or sleep problems are getting on top of you, please talk to your doctor or a mental health professional. If you ever feel you cannot cope or have thoughts of harming yourself, contact your local crisis line or your local emergency number straight away — support is available.

Prevention

You cannot always prevent heat rash, but you can greatly reduce the chance of getting it by avoiding overheating and letting sweat escape. Cooling the skin, wearing loose breathable clothing and keeping skin folds dry are the most effective steps — and they work for children and adults alike.

Vaccines

There is no vaccine for heat rash. Keeping up to date with routine vaccinations is still important for overall health, so speak to your doctor or health service if you are unsure.

Screening programmes

There is no screening test for heat rash. It is usually spotted by looking at the skin, and regular checks during hot weather — especially of babies and anyone who is less mobile — are the best way to catch it early.

Complications

If left untreated

• The skin can become infected, especially if it is scratched — look for spreading redness, warmth, swelling, pus or increasing pain
• Broken sleep and irritability from persistent itching
• Rarely, widespread heat rash can make it harder for the body to lose heat, which raises the risk of heat exhaustion in very hot conditions
• In people who are immobile or unwell, moist skin folds can become sore or infected
• Babies with heat rash may feed less well if they are uncomfortable and overheated

Long-term outlook

The outlook is very good. Most heat rashes clear up within a few days with simple cooling measures and do not come back unless the skin gets hot and sweaty again. It is not dangerous, it is not contagious, and it leaves no scars. Even if the skin becomes a little infected, it usually responds well once it is treated and kept cool and clean. If you are worried at any point, your doctor or pharmacist is there to help.

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