Heat Rash

A heat rash (also called a prickly heat rash or miliaria) is an area of your skin that gets irritated from sweat. The rash can be itchy and bothersome, but it’s usually harmless. You can typically care for a heat rash at home, and it’ll clear up within a few days.

Healthcare providers consider heat rash a mild form of heat-related illness. It’s not as serious as conditions like heat exhaustion or heat stroke. But if you’re exerting yourself in hot weather, a heat rash could be an early warning sign to cool down your body.

Symptoms of heat rash

A heat rash can make your skin feel like it’s:

• Burning
• Itchy
• Prickly

These sensations are uncomfortable and may make you want to scratch your skin. But resist that urge! Scratching your skin could cause it to break open, possibly leading to an infection.

What does heat rash look like?

A heat rash is a group of tiny bumps, similar to pimples or blisters. Typically, each bump is about 1 to 3 millimeters wide. The bumps often look red on light-colored skin. On darker skin, the bumps may look grey or white. The medical term for heat rash that causes these discolored bumps is “miliaria rubra.” This is the most common form of heat rash.

Heat rash can also appear as tiny, clear bumps. These look a bit like water droplets. Providers call this type of heat rash “miliaria crystalline.” It typically affects newborns but can also occur in adults. This is a milder form that may not cause itchiness or other discomfort.

Where do heat rashes form?

Heat rash often develops on areas of your body that don’t get enough airflow (for example, areas covered with clothing). It also tends to form in folds and creases where there’s skin-to-skin contact.

In babies, heat rash commonly forms in these areas:

• Armpits
• Elbow creases
• Neck
• Groin (diaper area)
• Upper chest and back

In adults, heat rash commonly forms in these areas:

• Arms
• Back
• Chest (especially under your breasts)
• Legs (especially on your inner thighs)

Heat rash causes

Sweat that’s trapped within your skin causes a heat rash. Normally, sweat glands in your skin make sweat and send it through tiny tubes (sweat ducts) until it reaches the surface of your skin. This sweat exits through openings on your skin (pores) and then evaporates to help cool your body down.

But clogs can sometimes form in your sweat ducts. A clog prevents sweat from finishing its journey to your skin’s surface. Instead, the sweat flows backward in the ducts. This causes inflammation within your skin’s outermost layer (epidermis) and/or middle layer (dermis). The inflammation results in a rash.

A clog can happen if:

• Too much sweat builds up between your skin and your clothing

and/or:

• Dead skin cells (corneocytes) build up in your pores or sweat ducts

If you’re sweating a lot, it’s easy for sweat to build up. The sweat softens dead skin cells on the surface of your skin and makes them more likely to build up in your pores or sweat ducts.

Risk factors

You may be more likely to develop a heat rash if you:

• Do intense physical activity, especially in the heat
• Have a fever
• Have a condition that makes you sweat more than expected (hyperhidrosis)
• Live in a hot or humid climate
• Need bedrest for a while (in this case, the rash may form on your back)
• Take medications that make your sweat glands more active, like beta-blockers, clonidine or opioids
• Wear tight clothing when working out or in warm environments

Babies, infants and toddlers have a higher risk because their sweat glands and ducts are still growing, and their bodies may not control their temperatures as well as adults do. They’re also often well-bundled or wearing multiple layers of clothing. And diapers aren’t very breathable!

Complications of prickly heat

It’s possible for heat rash to lead to a bacterial skin infection. This can happen if there’s a break in your skin (for example, from scratching), and bacteria enter. An infection can make the skin around the rash swell up or feel warm to the touch. You may also develop a fever, nausea and/or chills.

How doctors diagnose heat rash

You may not need to seek medical care for a heat rash. But if you do, a provider will:

• Ask you when the rash started, where it’s located and what symptoms you’ve had
• Review your medical history and any medications you’re taking
• Take a close look at your skin and (with your permission) touch the affected area
• Talk with you about things that might’ve caused the rash — like weather, physical activity or illness

All this information will help your provider diagnose heat rash or identify other issues that might be causing your symptoms. Conditions your provider may want to rule out (differential diagnoses) include:

• Bug bites
• Chicken pox
• Drug allergy rash
• Eczema or dermatitis
• Folliculitis

You don’t need any tests for a heat rash diagnosis. But you may need tests if your provider suspects another cause for your rash. In this case, your provider will tell you what to expect.

What is the treatment for heat rash?

It’s usually possible to get rid of a heat rash with at-home care. Here’s what to do as soon as you notice a rash forming:

• Move to a cooler or air-conditioned area, if possible.
• Remove clothing from the affected skin.
• Gently wash your skin in cool or lukewarm water and pat it dry (don’t scrub).
• Keep the area uncovered or put on clean, loose clothing that doesn’t rub against your skin.
• Apply a cool washcloth to your skin as needed to calm the prickly feeling.

These same basic tips apply no matter your age. If your child develops a heat rash, at-home care is usually enough. But call your pediatrician if your child keeps getting heat rashes or they last longer than a few days. They may want to rule out other common childhood skin conditions. In some severe cases, they may consider a medicated ointment to reduce itching or inflammation.

Tips while prickly heat rash heals

As the rash heals, it’s important to:

• Avoid using creams or other products that could block your pores. Sweat needs to come out. Lotions, creams, ointments and powders that might seem soothing can actually block your pores and keep sweat from coming out. This will make the rash worse.
• Limit activities that cause sweating. If possible, wait to work out or do other activities that cause excessive sweating until the rash is gone.
• Resist the urge to scratch. It’s so tempting. But scratching that itch can delay healing or even open up your skin to infection.
• Take cool showers. Taking frequent cool showers can help remove sweat from your skin.
• Use light bedding and wear light clothing. Avoid being bundled or wrapped up in blankets. Choose loose, airy clothes over tight, stretchy fabrics. For a baby, avoid over-bundling in too many layers or blankets, while still avoiding loose cloth or material that could get near your baby’s face. Let your skin or your baby’s skin breathe. When in doubt, air it out!

In general, you want to keep your pores open — and that means skipping creams and ointments. But applying an anti-itch cream (like calamine) may be necessary if the itching is intense. Talk to your provider or a pharmacist before using any topical products. They’ll help you choose the one that’s best for you.

When should I see my healthcare provider?

See a healthcare provider if:

• The rash doesn’t improve after a few days
• The rash is painful or causes intense itching
• You notice signs of a possible infection, like fever, chills, or skin that’s swollen or warm to the touch
• You’re concerned something else (besides heat) is causing the rash

How can I prevent heat rashes?

Keeping your skin cool and dry is the key to preventing heat rashes. That can be hard to do if you work outdoors or do sports or other activities in the heat. But whenever possible:

• Avoid spending time outside when it’s really hot or humid
• If you’re out in the heat, take frequent breaks to cool down
• Use air conditioning and/or fans to cool your indoor spaces
• Wear clothes that fit loosely and let your skin breathe (cotton fabrics are better than synthetic fabrics)

What can I expect if I have a prickly heat rash?

Once you cool and dry your skin, you can expect the rash to go away within a few days. You may want to talk to your healthcare provider about ways to avoid heat rashes in the future — especially if your job, hobbies or the climate where you live causes you to sweat a lot.