Heat Rash in Babies: What It Looks Like and How to Treat It

You notice tiny red or clear bumps spreading across your baby's neck, chest, or the creases of their skin after a warm day, and your mind jumps to the worst. Before you panic or reach for a heavy cream, take a breath. This is almost always heat rash, one of the most common and most harmless skin issues in infants, and it usually clears on its own within a day or two once your baby cools down.

Heat rash, also called prickly heat or miliaria, happens when a baby's sweat ducts get blocked and trap perspiration under the skin. Newborns are especially prone to it because their sweat glands are still developing. Here is how to recognize it, cool it down, and know when it is time to call your pediatrician.

What is heat rash in babies?

Heat rash is a rash that develops when the openings of your baby's sweat glands (eccrine ducts) become blocked, trapping sweat beneath the skin. The medical name is miliaria. Because a newborn's sweat ducts are not fully developed, they rupture more easily, which is why infants are particularly susceptible, especially in hot, humid weather or when they are dressed too warmly.

In babies, the rash mainly appears on the neck, shoulders, and chest. It also shows up in spots where skin rubs together or stays warm and damp, including the armpits, elbow creases, groin, diaper area, and along the hairline. Heat rash affects roughly 4.5% to 9% of newborns, so it is genuinely common.

What does baby heat rash look like? (The 3 types)

Not all heat rash looks the same. Dermatologists describe three types based on how deep the sweat-duct blockage sits in the skin. Most babies get one of the first two.

• Miliaria crystallina (mildest): 1 to 2 mm clear, fluid-filled blisters that look like tiny beads of sweat and break easily. They do not hurt or itch. This type often appears around 1 week of age and affects up to 9% of newborns.
• Miliaria rubra, or prickly heat (most common): clusters of small red, inflamed bumps, usually 2 to 4 mm, on a background of pink skin. These can be itchy and prickly, which may make your baby fussy.
• Miliaria profunda (rarest): firm, flesh-colored, goose-bump-like papules. This deep form is uncommon in infants.

How long does baby heat rash last?

The good news is that heat rash resolves quickly once the skin cools. Miliaria crystallina often clears within about 24 hours, and most heat rash settles within 1 to 2 days after you cool your baby down and remove whatever was trapping the sweat.

If the rash is still hanging around after several days of home care, or if it looks like it is getting worse rather than better, that is your cue to check in with a doctor rather than wait it out.

How to treat heat rash in babies at home

Treatment is about cooling the skin, not applying medication. The single most important step is to lower your baby's temperature and let trapped sweat escape. Thick ointments and heavy creams can actually make things worse by further blocking the sweat ducts, so skip those.

• Move your baby to a cooler, less humid spot and use a fan or air conditioning.
• Give a cool (not cold) bath or apply cool, moist compresses to the affected areas, then let the skin air-dry.
• Dress your baby in thin, loose-fitting cotton clothing, and remove extra layers. Overdressing is a very common trigger.
• Let the affected skin get some air time when you can.
• Avoid thick, occlusive ointments, powders, and heavy lotions that block the glands.

When to call your pediatrician

Heat rash is usually mild, but a few signs mean it is time to get your child seen. The American Academy of Pediatrics advises contacting your pediatrician if the rash does not improve after about 3 days of home treatment, or if it suddenly worsens within 24 hours.

You should also reach out promptly if you notice signs that the rash has become infected or that your baby is unwell, such as pus or yellow crusting, increasing tenderness or swelling, a fever, or your baby eating less or seeming unusually sleepy or inactive. For persistent miliaria rubra, a clinician may occasionally recommend a short course of a low-potency steroid cream, but that is a decision for a doctor to make, not something to try on your own.