Babies are more likely to get heat rash than adults because their sweat ducts are still developing. It can appear as bumps or blisters on the skin and usually resolves on its own.

Heat rash, which some people call prickly heat or miliaria, is a skin flare that occurs when sweat glands and ducts become blocked.

This causes sweat to flow back into the epidermis and dermis, the surface of the skin and the layer of tissue below it. These rashes can feel itchy, uncomfortable, and prickly.

Although anyone can get heat rash, babies are more susceptible because they have immature sweat ducts.

Miliaria occurs when the skin traps sweat. The sweat irritates the outer layer of the skin and causes a rash.

With rashes that cause redness, the redness may be easier to see on light skin and more challenging to see on dark skin, though the process causing the discoloration is the same.

Doctors divide heat rash into the following three types according to its severity.

Miliaria rubra

Miliaria rubra, or “prickly heat,” is the most common type of heat rash and commonly affects newborn babies ages 1 to 3 weeks.

This type of rash develops when there is a blockage in the sweat glands near the epidermis (the surface of the skin) and the dermis (the layer of tissue underneath).

Symptoms of miliaria rubra include:

  • tiny, red bumps or blisters
  • discoloration such as redness
  • itching

Miliaria rubra often itches, so babies may persistently scratch their skin.

If the rash has spots containing pus, it is called miliaria pustulosa. This may indicate a bacterial infection.

Miliaria crystallina

Miliaria crystallina or sudamina is common in newborn babies, particularly those ages 2 weeks or under. It is the least severe form of heat rash. It happens when there is a blockage in the sweat glands in the epidermis.

The only symptom of miliaria crystallina is tiny clear or white blisters that resemble water droplets. They do not look red or inflamed.

The rash usually resolves within a few days after the affected layer of skin rubs off.

Miliaria profunda

Miliaria profunda is the most severe type of heat rash, but it is uncommon.

When sweat repeatedly leaks into the dermis, it can cause intense flushing and burning. Babies with extensive miliaria profunda may also develop signs of heat exhaustion as their blocked sweat glands stop producing sweat to cool them down.

Symptoms of miliaria profunda include firm, large, flesh-colored spots that may look like pimples and mild to intense itching.

Additionally, if a baby scratches their rash, they can contract an infection.

For most babies, the only symptom of heat rash is a rash on parts of the body that have had heat exposure.

Swaddling, warm clothes, unsuitable ventilation, and being near heat sources, such as space heaters, can all increase the risk. A parent or caregiver might notice a rash on an area of the body that became particularly warm.

Heat rashes are also more likely to appear in skin folds, such as in the neck or groin.

In most cases, heat rash clears up fairly quickly and does not cause too much discomfort, so it may not require medical attention.

The signs of a heat rash are obvious, especially in hot weather. If a parent or caregiver is unsure about a rash, a doctor can usually diagnose it according to its appearance.

Miliaria may go away on its own within a few days without treatment.

Parents and caregivers may be able to ease a baby’s discomfort and speed up healing with the following methods:

  • Move the child to a cool area at the first sign of a heat rash.
  • Keep their skin cool and dry.
  • Apply a cool compress to the affected area.
  • Rinse away oil and sweat with cool water, then gently pat the area dry.
  • Regularly clean skin folds to make sure trapped sweat and oil do not worsen the rash.
  • Dress the baby in loose, breathable fabrics, such as cotton.
  • Keep the baby well-hydrated. This may involve nursing breastfed babies on demand and ensuring that older babies have constant access to water.

Do not use rash creams on the skin unless a doctor recommends a specific cream. A heat rash is not an allergic reaction, so using creams that treat these conditions may not help.

For severe heat rashes or rashes that do not go away on their own, a doctor might prescribe a steroid cream to speed up healing.

Sometimes, heat rashes can cause an infection, especially if a baby scratches the affected area. A heat rash with an infection may cause a fever and other signs of illness.

If a baby has a fever or seems sick, a parent or caregiver can speak with a doctor for more help. Healthcare professionals may prescribe antibiotics to clear up any bacterial infection.

Heat rash occurs due to the skin trapping sweat. Children and babies cannot regulate their temperature as well as adults, so anything that makes them too hot may increase the risk of heat rash.

Examples include:

  • wearing clothes that are too warm for the season
  • living in a very warm climate
  • sitting near heat sources, such as space heaters or heat lamps
  • swaddling, especially if the weather is warm or the baby is sweating
  • having thick creams or oils on the skin that can block sweat ducts

To reduce the risk of heat rash in babies, parents and caregivers can try the following:

  • Dress babies in seasonally appropriate clothing. There is no need for babies to always be in a swaddle or under a blanket, especially in warm weather.
  • Choose loose-fitting, breathable clothing, such as cotton pants or a gown.
  • Keep babies out of direct sunlight.
  • In hot weather, use air conditioning and fans to keep babies cool.
  • Avoid putting babies directly in front of space heaters or other heat sources.
  • Monitor babies for signs of excess sweating. If a baby looks flushed or is sweating, move them to a cooler area.

If a baby’s skin is kept cool, heat rash usually resolves within a few days without treatment.

Heat rashes appear when sweat gets trapped under the skin. Because babies have smaller sweat glands and are less able to regulate their body temperature, they are more vulnerable to heat rash than adults.

Tight clothes, swaddles, and blankets can also increase the risk of heat rashes. In most cases, the rash will go away without treatment.

Heat rash is not usually dangerous. However, it can indicate that a baby is at risk of overheating. Overheating can cause serious health issues, so it is important to heed the warning and move the baby to a cooler spot.

Keeping an infant cool and comfortable can quickly clear up the rash.

If the rash does not go away on its own within a couple of days, the baby seems very uncomfortable, or the rash begins spreading, parents and caregivers should speak with a doctor.