It's a warm afternoon and you're doing a diaper change when you notice tiny red bumps clustered across your baby's neck, chest, or back (they weren't there this morning). Now you're wondering what you're looking at — and whether you need to do something about it.
More often than not, what you're seeing is heat rash, one of the most common skin conditions in babies. It's almost always harmless, and usually clears up quickly once your baby cools down. Here's how to recognize it, treat it, and keep it from coming back.
Key Takeaways
What Is Baby Heat Rash?
Heat rash (also called prickly heat, or miliaria in medical terms) happens when sweat gets trapped under the skin. Babies are especially prone to it because their sweat glands are still developing — they can't regulate their body temperature the way older kids and adults can, and their skin folds create plenty of spots for heat and moisture to build up.
It's most common in warm weather, but can happen any time a baby overheats: bundled too warmly in winter, placed in a car seat for a long drive, or simply sleeping in a room that's too warm.
Types of Heat Rash: What You Might See
Not all heat rash looks the same. There are a few variations, and the appearance depends on how deep the blocked sweat ducts are.
Miliaria crystallina is the mildest form of heat rash. It shows up as tiny clear or white fluid-filled blisters, usually on the surface of the skin. They're fragile and can burst easily. You'll most often see this on a newborn's face, neck, or upper chest.
Miliaria rubra is the most common type of heat rash, and what most people mean when they say "prickly heat." Small red bumps or blisters, often with a slight stinging or itchy sensation. It tends to show up in the skin folds: neck, armpits, chest, groin. This is the one that may make your baby fussy or uncomfortable.
Miliaria profunda is rare in infants. It sits deeper in the skin and looks more like firm, flesh-colored bumps. If you're seeing something that doesn't look like either of the above, it's worth a call to your pediatrician to rule out other causes.
Is It Heat Rash — or Something Else?
A few other newborn skin conditions can look similar. Here's a quick guide to telling them apart:
Baby acne shows up as red or white bumps mostly on the face (cheeks, chin, forehead). It's caused by maternal hormones, not heat, and tends to appear between two and six weeks of age. It doesn't come and go with temperature changes.
Eczema typically appears after two months and looks more like dry, scaly patches. It tends to stick around longer and often comes with real itchiness. Heat can make eczema flare, but the root cause is different.
Drool rash is localized around the mouth and chin. It's caused by skin irritation from saliva, not sweat.
Allergic reactions can cause widespread redness or hives. If the rash is spreading quickly or your baby seems unwell, call your pediatrician.
The clearest sign you're dealing with heat rash: it showed up during or after a period of overheating, it's clustered in warm or covered areas, and it improves once your baby cools down.
How to Treat Baby Heat Rash
The good news: heat rash usually doesn't need treatment. Cooling your baby down is often enough to clear it up within a day or two.
Cool the skin. Move to a cooler room, remove extra layers, and let the skin breathe. A lukewarm bath can help — pat dry thoroughly, especially in the folds, afterward.
Dress them lightly. Loose, lightweight clothing in natural fabrics (cotton is ideal) lets heat and moisture escape. Avoid synthetic fabrics that trap warmth against the skin.
Skip the creams and powders. It's tempting to apply something, but most lotions and creams can actually make heat rash worse by trapping more moisture. Baby powder is not recommended for infants because of inhalation risk. Leave the skin clean and dry.
Keep the room cool and well-ventilated. Consistent ambient temperature matters more than any topical treatment. The American Academy of Pediatrics recommends keeping a baby's sleep environment between 68 and 72°F (20–22°C).
Most cases of miliaria rubra clear up within two to four days with these steps. If the rash isn't improving, is getting worse, or your baby develops a fever or seems unwell, call your pediatrician.
How to Prevent Heat Rash
Prevention comes down to one thing: keeping your little one from overheating. In practice, that means thinking about clothing, room temperature, and the surfaces your baby spends time on.
Dress for the room, not for the weather. A common rule of thumb: one more layer than what you're comfortable in. But it's easy to over-bundle, especially with newborns. Check the back of the neck or the chest, not the hands, to gauge whether your baby is actually warm.
Keep the sleep environment cool. Overheating during sleep is both a heat rash trigger and a safe sleep concern. A room that's too warm, combined with heavy swaddling or a non-breathable mattress surface, creates exactly the conditions where sweat gets trapped.
Think about what your baby sleeps on. Most standard crib mattresses are made with foam, which retains heat. Newton's Wovenaire® core is made of 90% air and 10% food-grade material, with no foam, glue, latex or springs. Air moves through the mattress rather than getting trapped inside it, which means your baby's sleep surface doesn't work against you when it comes to temperature regulation.
Limit time in hot spots. Car seats, bouncy seats, and carriers all trap heat against your baby's back. They're necessary, but it's worth building in breaks on warm days and avoiding heavy cover-ups over the seat when you're not in direct sun.
Watch the layering in cooler months. Heat rash isn't just a summer problem. Overdressing a baby in winter — snowsuits, blankets, warm cars, indoor heating — creates the same conditions as a summer heat wave.
When to Call Your Pediatrician
Most heat rash is harmless and resolves quickly. But call your pediatrician if:
- The rash isn't clearing up after three to four days of cooling measures
- The bumps look infected: pus-filled, swollen, or warm to the touch
- Your baby has a fever alongside the rash
- Your baby seems unusually uncomfortable, lethargic, or difficult to settle
- You're not sure what you're looking at
Severe or persistent heat rash can occasionally indicate that a baby isn't regulating temperature well. In rare cases, it can lead to secondary skin infections. When in doubt, reach out.
