Key takeaways: Heat rash (miliaria) happens when the openings of sweat glands get blocked and sweat is trapped under the skin. It looks like tiny red bumps or tiny fluid-filled blisters, most often on the upper chest and back, neck folds, hairline, and diaper area. Cool your baby’s skin, dress them in thin, loose cotton, and skip thick, greasy ointments. Call your baby’s doctor if the rash is tender or draining pus, your baby has a fever, is eating less or less active, or the rash isn’t gone after 3 days of home care or gets worse over 24 hours.
Heat rash is very common in the first few weeks of life, according to the American Academy of Pediatrics (AAP). You may also hear it called “sweat rash” or “prickly heat.” Most of the time it’s harmless and fades once your baby’s skin cools down, but it helps to know what it looks like and when a rash needs a closer look.
What It Looks Like
- Tiny red bumps, or tiny clear, fluid-filled blisters, usually in patches.
- Most common on the upper chest and back, neck folds, hairline, and under the diaper, though it can show up almost anywhere.
- It can be itchy, so your baby may seem fussier or more wiggly than usual.
Why Babies Get It
Heat rash develops when the openings of sweat glands become blocked, so sweat gets trapped under the skin. The AAP lists these situations as raising the risk:
- Hot, humid weather.
- Tight clothing or too many layers.
- Being tightly wrapped in blankets.
- Long stretches buckled into a car seat or other seat where air can’t flow well.
From the author
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How to Treat Heat Rash at Home
These are the home-care steps the AAP recommends:
- Cool the skin. Give a cool bath or use cool, moist compresses, then dry the skin completely.
- Let the skin breathe. Leave the affected areas uncovered when you can.
- Dress in thin, loose cotton that lets air flow without getting tangled around your baby.
- Clean and cool skin folds gently, including the neck, armpits, and the creases of the elbows and legs.
- Use air conditioning or a gently blowing fan to keep the room comfortable.
- Avoid thick, greasy ointments on the rash, because they can block sweat glands even more.
The AAP’s heat rash guidance doesn’t recommend any creams or medicines for typical heat rash. Before putting hydrocortisone or any other product on your baby’s skin, check with your baby’s doctor.
Preventing Heat Rash
- In warm weather, dress your baby in loose cotton clothing and skip extra layers and tightly wrapped blankets.
- Use fans or air conditioning on hot days.
- Limit time in very hot places, and avoid leaving your baby strapped into a seat for long periods.
- For sleep, the AAP also recommends avoiding overheating and keeping your baby’s head uncovered. See how to dress your baby for sleep.
- Never leave your baby alone in a car, even for a minute. See hot car safety.
Is It Heat Rash or Something Else?
Many newborn rashes look alike, and photos online can be misleading. Heat rash tends to show up in warm, covered, or sweaty areas and improves within a few days once your baby cools down. Other common rashes behave differently:
- Baby acne and milia usually show up on the face, not specifically in sweaty areas. See baby acne, cradle cap, and eczema.
- Eczema tends to look dry, rough, and scaly, and it doesn’t clear just because your baby cools off.
- A rash with fever needs a call to the doctor, whatever it looks like. See rashes with fever.
If you aren’t sure what a rash is, your baby’s doctor can usually tell by looking at it. A photo of how the rash looked at its worst can help, since rashes often change throughout the day.
Call your baby’s doctor if: the rash is tender or draining pus, your baby has a fever, is eating less or seems less active, or the rash isn’t gone after 3 days of home treatment or is getting worse over 24 hours. If your baby is 3 months old or younger and has a rectal temperature of 100.4°F (38°C) or higher, call right away.
The Bottom Line
Heat rash is common, especially in the first weeks of life. Cool your baby’s skin, dress them in thin, loose cotton, skip heavy ointments, and it usually fades within a few days. Call if you see signs of infection, fever, or a rash that’s lasting or getting worse.
Want more support for your baby’s first year? My book, From First Breath to First Birthday, is available on Amazon.
Related Articles
- Baby Acne, Cradle Cap, and Eczema: Telling Them Apart
- Baby Sweating: When It’s Normal and When to Ask
- Diaper Rash: Prevention, Treatment, and When It’s Yeast
- Rashes With Fever: Which Ones Need Urgent Care
Sources
- Weber B, Asch S; American Academy of Pediatrics Section on Dermatology. Heat rash. HealthyChildren.org. Updated September 12, 2024. https://www.healthychildren.org/English/ages-stages/baby/bathing-skin-care/pages/Heat-Rash.aspx
- Moon RY, Carlin RF, Hand I; Task Force on Sudden Infant Death Syndrome. Sleep-related infant deaths: updated 2022 recommendations for reducing infant deaths in the sleep environment. Pediatrics. 2022;150(1):e2022057990. https://doi.org/10.1542/peds.2022-057990
- Nationwide Children’s Hospital. Fever in a newborn baby (Helping Hand HH-I-105). Revised February 2022. https://www.nationwidechildrens.org/conditions/health-library/fever-ina-newborn-baby
Last updated November 3, 2026. This article is for general education and is not a substitute for individualized medical advice. Always talk with your baby’s health care provider or your own provider about your specific situation. If you think your baby or you may have a medical emergency, call 911.
