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Prickly heat (heat rash): symptoms, treatment, and prevention

October 13, 2022 • read

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Prickly heat (heat rash): symptoms, treatment, and prevention

Hot and humid conditions are ideal for developing prickly heat rash, but they’re not its only cause. Heat rash can be a byproduct of your self-care if you enjoy hot yoga, exercise frequently, or use steam rooms or saunas. Even adding your winter layers too prematurely or throwing an additional duvet onto the bed can trigger it. Here’s everything you need to know about prickly heat rash and what to do about it.

What is prickly heat?

Prickly heat rash is pretty aptly named. It’s a prickly, itchy, and sometimes stinging rash that develops on your skin as a result of heat. Also known as eccrine miliaria or heat rash, the condition occurs when your sweat glands become obstructed. Because of this, sweat is trapped in the skin, resulting in a skin rash.

There are three types of eccrine miliaria — miliaria crystallina, miliaria rubra, and miliaria profunda. The type of heat rash that develops depends on the part of the sweat duct affected, and each has a slightly different presentation.

Heat rash can sometimes be hard to self-diagnose as it can look like a number of other skin conditions and rashes. If you’re having trouble identifying or treating your skin issue, Maple can help. Maple is a virtual care platform that connects you with Canadian-licensed doctors and specialists. With Maple, you can get to the bottom of your skin dilemma by seeing a doctor or dermatologist online from your phone, tablet, or computer.

Who can develop prickly heat?

Under the right circumstances, anyone can develop prickly heat rash, but here are some of the most likely groups.

Newborns and babies are highly prone to heat rash because their sweat glands are just developing. Additionally, they’re also less able to control their internal body temperature. Add that to the tendency for new parents to overdress their little ones, and you’ve got the perfect conditions for developing heat rash.

Babies aren’t the only population with an increased risk for the condition though. Being on bedrest increases your odds of developing prickly heat rash. Remaining in place for long periods of time — like in one position in a bed — hampers air flow to the immobilized areas. Besides precipitating irritation, this also limits the flow of sweat off your body.

Being confined to bed can result in heat rash even under cool or air-conditioned circumstances. But hot and humid conditions — like being in a building without air conditioning in the summer — up its probability.

Additionally, being overweight or obese may amplify your chances of experiencing the condition. This is due to the rolls of skin these individuals are more likely to have. Since the skin folds between these rolls are more likely to retain moisture, rub against each other, and occlude sweat glands, they make prickly heat rash more likely.

What causes prickly heat?

When your body can’t expel your sweat properly through your sweat ducts, it becomes trapped in your skin. With nowhere else to go, this sweat can spread under the surrounding skin, triggering an itchy, inflamed rash.

Keep in mind that heat rash isn’t contagious. However, heat rash can spread all over the body. It can also be triggered by a fever.

Another common cause of heat rash is travelling to a hot and humid climate. In this case, the condition usually resolves as your body acclimatizes to the new weather.

While anything that obstructs the sweat glands can trigger heat rash, certain causes are especially notable. A big one tends to be wearing constricting or synthetic fabrics that don’t allow for air flow — especially during high-intensity exercise. Prolonged bed rest is another as bedding can function as a barricade blocking your body’s sweat glands. Lightweight bedding is one way to help prevent heat rash.

What are the symptoms of prickly heat?

As its name suggests, prickly heat typically causes a prickly or itchy sensation in the skin. With miliaria rubra, the rash manifests in small uniform bumps between 2 to 4mm — about the size of tiny glass beads. You’re most likely to find it in areas that experience a lot of friction like around the collar, under your arms or breasts, or in the creases of your knees and elbows.

Alternatively, heat rash can present as tiny, 1 to 2mm bumps resembling glass beads. This is the case with miliaria crystallina, which is most likely to crop up on the head, neck, and upper trunks of infants, and mainly on the trunk for adults.

Finally, miliaria profunda appears as 1 to 4mm bumps on the trunk and extremities. These can be either skin-coloured or red.

What does prickly heat look like?

Prickly heat rash can look slightly different depending on the person experiencing it. It often appears as small raised red bumps, although the redness of the rash on the skin may not be as obvious on black or brown skin, or darker skin tones. Alternatively, the rash can appear as clear, fluid-filled bumps, leading many to compare it to acne.

How can you prevent heat rashes?

Wearing loose-fitting, lightweight cotton clothing is one of the best ways of avoiding heat rash. Thick and synthetic fabrics are more likely to trap heat, leading you to sweat. To avoid heat rash on hot days or while exercising, focus on wearing light layers that you can remove as you heat up. You’ll also want to drink plenty of water to avoid dehydration.

Newborns and small babies are more vulnerable to heat rash and can’t tell you when they’re getting too hot. While fall weather can tempt you into breaking out your baby’s thick winter sleep sack, unless you’re camping they’re probably unnecessary. Most houses sit somewhere around 21°C (70°F). This means that even when the thermometer dips outside, your baby’s room is likely pretty comfortable.

To ensure your baby is warm enough, avoid touching their hands or face. Because of their distance from your baby’s core, these will feel cool to the touch even when your baby is perfectly comfortable.

Instead, place a hand on your little one’s back or belly. If these feel warm, there’s no need for another layer. It’s hard not to worry, but your baby doesn’t require more layers than you do.

To further avoid repeat heat rashes, consider doing the following:

  • Limit your exposure to hot and humid conditions, including steam rooms and saunas
  • Cool off after sweating or an intense exercise session with a lukewarm shower
  • Seek out air conditioning or use a fan when it’s hot
  • Treat fevers with antipyretic, or fever-reducing medications like acetaminophen or ibuprofen

How long does prickly heat usually last?

The good news is that prickly heat rash doesn’t stick around for that long. Your symptoms should resolve within a day or two. If they’re not markedly better after day four, consider speaking with a healthcare provider.

Can you get rid of prickly heat fast?

Because prickly heat rash can result in inflammation, soothing your skin is often a good start to addressing the condition. A great way to do that is by using a cooling compress, or by wrapping an ice pack in a towel and applying it to the affected area. You’ll also want to avoid scratching the rash if possible to help prevent infection.

Additionally, you can take an antihistamine. This will help to calm the swelling and reduce the itchy, prickly feeling that the rash brings. But, while you can minimize the worst of its effects, these strategies won’t get rid of prickly heat rash entirely. Luckily, the condition should clear up within a day or two.

What are the most common treatments for prickly heat?

In addition to ice and antihistamines, there are a few other ways to soothe the redness, itching, and discomfort of your prickly heat rash. These include:

  • Taking an oatmeal bath — while keeping your heat rash dry is important, bathing in oatmeal is an exception. Oatmeal contains avenanthramides, which are compounds with anti-inflammatory and anti-itch properties that help to soothe your skin. Just make sure to gently pat yourself dry afterwards instead of rubbing off with a towel. Exposing your damp skin to friction can make your rash worse.
  • Applying an over-the-counter (OTC) hydrocortisone cream — this can help to relieve the worst of your symptoms. If your symptoms are severe or the area of your rash is quite large, however, you may require a prescription hydrocortisone cream.
  • Applying calamine lotion — this may help to calm the itching associated with your heat rash.
  • Using aloe vera — this helps to soothe rashes caused by prickly heat. Aloe is often used for treating sunburns due to its cooling and anti-inflammatory properties, and despite being a gel-like substance, it won’t block your pores. This makes it safe for addressing prickly heat rash.
  • Keeping the affected area dry and cool. Heat and friction got you here in the first place, and exposing your rash to them will only make it worse. Do your best to keep your skin cool and dry until it’s had the chance to heal. While you’re at it, avoid ointments or other topicals that will block your pores, as this may worsen the rash.

When to see a doctor for heat rash

Heat rash will usually disappear on its own within a few days. While it can be uncomfortable, you’re unlikely to need to see a doctor.

In certain circumstances, however, you should speak to a doctor about your prickly heat rash. These include if your rash isn’t getting better, or seems to be getting worse after day three or four, as it’s a possible sign that you’ve developed a secondary infection. Likewise, if your heat rash is extremely painful, it’s a good idea to see a healthcare provider. They may be able to prescribe hydrocortisone cream to clear it up quicker.

In young children or those who are immunocompromised, some symptoms may indicate a secondary infection. If your child has what looks like heat rash and any of the following, it warrants a visit with their healthcare provider:

  • An accompanying fever
  • Swelling around the rash
  • Drainage of pus from the affected area
  • Chills

Additionally, if your heat rash is accompanied by headache, dizziness, nausea or vomiting, or feeling very weak or thirsty, you may be experiencing heat exhaustion or heatstroke. While you can usually deal with heat exhaustion safely at home, heatstroke is a medical emergency and requires immediate intervention.

If you’re not sure whether you’re experiencing heat rash, it’s a good idea to speak to a dermatologist for clarification. Some skin cancers can appear as rashes in their early stages, making proper diagnosis crucial. While seeing a dermatologist can take months, with Maple, getting a dermatology consultation takes less than 24 hours. Even better, you don’t need a referral.

If you’re experiencing heat rash and need treatment and medical advice, reach out today. Put that stinging, itchy feeling to rest and go back to feeling comfortable in the skin you’re in.

This blog was developed by our team and reviewed by a medical professional. 

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