Miliaria rubra is a type of heat rash or prickly heat that happens when sweat becomes trapped under the skin. Children tend to get it more than adults because their sweat glands are still developing.

Prickly heat is also called heat rash or sweat rash. There are three types of heat rash, depending on severity:

  • Miliaria crystallina: This type is mild and occurs on the sweat ducts close to the surface of your skin.
  • Miliaria rubra: This type occurs in deeper layers of the skin.
  • Miliaria profunda: This type is the most severe. It results from sweat leaking from the sweat glands into the middle layer of the skin after repeated episodes of miliaria rubra.

Miliaria rubra is uncomfortable and itchy. However, developing the rash isn’t usually enough to visit a doctor unless you have more concerning symptoms that can indicate a skin infection.

Keep reading to learn about the symptoms and causes of this type of prickly heat rash and how to treat and prevent it.

The symptoms of the prickly heat rash miliaria rubra are fairly straightforward. They typically include:

These bumps tend to develop in folds of skin and places where your clothing rubs against your skin. They tend to appear on the trunk and extremities.

The area of irritation might display a reaction right away, or it might take a few days to develop on your skin.

Sometimes, prickly heat takes the form of a patch of very small blisters. This is your skin reacting to the sweat that’s leaked between its layers. Other times, the area of your body where sweat is trapped might appear swollen or itch persistently.

Though less common, a person with miliaria rubra may also develop pustules, or pus-filled bumps, on their skin. This is known as miliaria pustulosa, and it may indicate a bacterial infection.

Prickly heat rashes result from trapped sweat. This can happen due to:

  • hot, humid weather
  • prolonged exercise
  • fever
  • wearing synthetic clothing that doesn’t allow sweat to evaporate
  • excessive sweating due to certain medications
  • laying for too long on a damp mattress with a waterproof cover, such as while hospitalized

When you sweat more than usual, your glands can become overwhelmed. The sweat ducts may become blocked, trapping the sweat deep underneath your skin. Sweat can also permeate the upper layers of the skin, becoming trapped beneath the epidermis.

Getting prickly heat at any time of year is possible, but it’s most common in the warmer months. Some people who are used to cooler climates tend to experience heat rash when they travel to tropical places with significantly higher temperatures and humidity.

Children, especially infants, are particularly vulnerable to prickly heat. Their sweat glands aren’t yet fully developed, and their skin isn’t used to rapidly changing temperatures.

Like most baby rashes, prickly heat is usually harmless and will go away on its own.

Symptoms may include:

  • a bumpy rash that occurs on their face and in the folds of their skin around the neck and groin
  • being cranky and difficult to soothe if the rash is itchy
  • being overheated or dehydrated
  • fever

How to manage prickly heat rash on a baby

If you notice a small patch of tiny red blisters beneath your child’s skin, evaluate their surroundings. Are they wearing too many layers? Is their clothing appropriate for the temperature? If possible, relocate them to a cooler environment or remove layers of clothing.

A cool bath may also provide relief for your child in most situations. Keep their skin dry when it’s not bathtime. Avoid oil-based products, as they could clog the pores further.

If your baby has a fever over 100.4°F (38°C) or other symptoms, call their pediatrician.

Heat rash, including prickly heat, often goes away without treatment.

The first step to soothing prickly heat is to move away from the irritant (or environment) causing your skin to break out in a sweat. Once you’re in a cooler environment, such as an air-conditioned room, the sensation of itching underneath your skin might take a while to subside.

You can also try:

  • wearing light, loose-fitting clothing made of natural materials, like cotton
  • avoiding clothing made of synthetic materials, like polyester
  • avoiding skin products that contain petroleum or mineral oil
  • avoiding perfumed soaps or body care products
  • applying a cold compress, which you can make at home using a plastic bag or towel

Over-the-counter products for prickly heat

Various over-the-counter (OTC) products are available to help treat prickly heat.

Calamine lotion is a natural remedy for prickly heat. You can apply it to the affected area to cool the skin.

Other products to try include:

If prickly heat is associated with a fever, you may consider fever reducers such as ibuprofen (Advil, Motrin) or acetaminophen (Tylenol). Speak with a healthcare professional before giving one of these medications to a child. Never give aspirin to a child or young teenager, as it can increase the risk of Reye syndrome.

Prescription treatments for prickly heat

Most people generally manage prickly heat rash without medical attention.

However, if the rash is widespread, doesn’t go away, or is bothersome, a healthcare professional may recommend a topical corticosteroid cream, such as triamcinolone 0.1% cream (Triderm). This topical corticosteroid is only available by prescription in the United States.

If you develop a skin infection as a complication of prickly heat rash, a healthcare professional may prescribe a topical antibiotic such as clindamycin.

The most effective way to avoid prickly heat is to avoid situations that cause excessive sweating. Try these tips:

  • Wear loose-fitting cotton clothing if you know you’re going to be in a hot or humid climate.
  • Take cool baths or showers frequently when visiting a hot or humid climate.
  • If you’re in a hot or humid climate, spend a few hours each day in a cool space with fans or air conditioning.
  • Opt for lightweight bedding, such as cotton or linen sheets.
  • When you exercise outside, choose gear that will wick moisture away from your skin.
  • Make sure to change out of sweaty or wet clothing right away after experiencing intense heat.
  • Change your baby’s diaper immediately after they wet or soil it.
  • Stay well hydrated by drinking plenty of fluids.

Heat rash usually goes away on its own. If it seems to be getting worse or the area is becoming infected, consider talking with a doctor.

Remember that bacteria live on your skin. Excessive itching can create an open wound that can then become infected.

Some people have hyperhidrosis, a condition in which their bodies produce too much sweat. If you suspect you’re sweating too much, you may want to talk with a doctor, such as a dermatologist. Hyperhidrosis can also develop if you take certain medications.

If you notice prickly heat appearing on your skin, be mindful of what your body is trying to tell you. Make sure to stay hydrated in warm climates and during physical activity.

Watch for other symptoms of heat exhaustion (such as dizziness, headache, or rapid heart rate) and move to a cooler area as soon as you can.

Prickly heat, or miliaria rubra, is a type of heat rash that develops when sweat becomes trapped in the skin, usually around the skin folds. It’s typically caused by sweating, whether from being in a hot, humid climate, engaging in intense exercise, or due to another reason.

You can generally treat a prickly heat rash by cooling down or with over-the-counter products.

It’s possible to develop a secondary skin infection from frequent itching. An infection may require a prescription antibiotic to resolve. If you develop pus-filled bumps or other concerning symptoms such as a fever, consider talking with a healthcare professional.