Baby heat rash is a common, usually harmless rash of tiny bumps or clear blisters that appears when trapped sweat blocks your baby’s sweat ducts, and it typically clears within a few days once you cool your baby down and dress them in light, loose cotton.
You undress your baby after a warm afternoon and find a patch of tiny bumps across the neck and chest. Baby heat rash is one of the most common reasons for that, and it is one of the easier rashes to treat: the main fix is less heat.
Below: what heat rash looks like on light and dark skin, the four types, what helps and what to avoid, how it compares with other rashes, how it ties to safe sleep, and when to call your pediatrician.
Key Takeaways
Heat rash happens when blocked sweat ducts trap sweat under the skin, usually from heat, humidity, overdressing or fever.
It looks like tiny red bumps or clear blisters; on darker skin the bumps may look gray or white.
Treat it by cooling your baby, drying skin folds and dressing them in thin, loose cotton.
Skip thick ointments, creams and powders, which can block sweat ducts further.
Call right away for a fever in a baby under 3 months, a rash with fever, pus, or spots that do not fade when pressed.
Table of Contents
Baby Heat Rash: The Short Answer
Quick Answer
Baby heat rash (miliaria, or prickly heat) is patches of tiny bumps or small fluid-filled blisters, usually in the neck folds, upper chest and back, hairline or diaper area, caused by sweat trapped under the skin. Cool your baby down, dress them in thin, loose cotton and skip thick creams. It usually clears within a few days.
The American Academy of Pediatrics (AAP) describes heat rash as common in babies and young children, especially in hot, humid weather. It can itch, so your baby may seem fussier than usual. Cleveland Clinic calls it usually harmless, a mild form of heat-related illness far less serious than heat exhaustion or heat stroke.
Still, a rash in a very young baby deserves a closer look. MedlinePlus (National Library of Medicine) advises contacting your provider about any rash, spots or blisters in a baby younger than 3 months.
What Heat Rash Looks Like on Different Skin Tones
Heat rash looks like clusters of very small bumps. Cleveland Clinic says they are typically about 1 to 3 millimeters wide.
On lighter skin: the bumps look red (Cleveland Clinic).
On darker skin: Cleveland Clinic notes the bumps may look gray or white instead of red, which makes them easy to miss.
Clear, dewdrop-like bumps: the mildest type looks like tiny clear water droplets. Cleveland Clinic says it mostly affects newborns and may not itch.
Location, timing (did it appear after your baby was warm or sweaty?) and whether it fades as your baby cools tell you more than color. Flat purple, red or brown spots that do not fade when pressed are a different, urgent situation.
Where Heat Rash Shows Up on Babies
Heat rash appears where sweat has trouble escaping. The AAP and Cleveland Clinic list these common spots in babies:
Neck folds: folds trap heat, sweat and drool.
Upper chest and back: especially under clothing layers.
Armpits and elbow creases: skin-on-skin areas that stay damp.
Diaper area and groin: Cleveland Clinic notes diapers are not very breathable, which adds to the risk.
Hairline and scalp: listed by the AAP.
The AAP adds that heat rash can occur almost anywhere on the body. On the face, compare it with baby acne and drool rash using the table below.
What Causes Heat Rash in Babies?
Heat rash starts when sweat ducts become blocked. Sweat gets trapped under the skin and causes small bumps, itching or prickling. The AAP says this is especially likely when a child is overheated or has limited airflow, such as from wearing many layers, being wrapped in blankets or being buckled into a car seat.
Cleveland Clinic explains why babies are more prone than adults:
Developing sweat glands: a baby’s sweat glands and ducts are still growing.
Immature temperature control: babies cannot regulate body temperature as well as older children.
Bundling: babies are often dressed or wrapped in extra layers.
Diapers: diapers hold heat and moisture against the skin.
Other triggers named by Cleveland Clinic and StatPearls (an NIH clinical reference) include hot, humid weather, fever, and tight or non-breathable clothing. So an overdressed baby in a warm house in January can get it too.
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Doctors sort heat rash by how deep in the skin the sweat duct is blocked.
Type
Where the blockage is
What it looks like
Notes
Miliaria crystallina
Very top layer of skin
Tiny clear blisters, 1 to 2 mm, that break easily
Common in newborns; StatPearls says it affects about 4.5% to 9% of newborns, most often at 2 weeks of age or younger
Miliaria rubra (prickly heat)
Slightly deeper in the outer skin
Small red bumps and blisters; red on lighter skin, gray or white on darker skin
The most common type; StatPearls notes it is often seen in newborns 1 to 3 weeks old
Miliaria pustulosa
Same as rubra
Rubra bumps that fill with pus
May point to a bacterial infection (StatPearls): call your pediatrician
Miliaria profunda
Deepest level, where the outer skin meets the dermis
Larger, firm, flesh-colored bumps
The rarest type (StatPearls)
Types of heat rash by depth. Sources: StatPearls (NCBI Bookshelf), Miliaria; Cleveland Clinic, Heat Rash.
How to Treat Baby Heat Rash at Home
The treatment is removing the heat. The AAP and Cleveland Clinic recommend:
Move to a cooler spot: shade or an air-conditioned room, or use a gently blowing fan (AAP).
Cool the skin: a cool bath or cool, moist compresses (AAP); wash gently without scrubbing (Cleveland Clinic).
Dry completely: pay extra attention to the neck, armpits and elbow and leg creases, which collect sweat and drool (AAP).
Let the skin breathe: leave the rash uncovered when you can (AAP).
Dress light: thin, loose cotton that does not tangle (AAP); Cleveland Clinic prefers cotton over synthetics.
Watch for the signs of overheating the AAP lists in its safe sleep guidance (sweating, a hot chest and flushed skin) and remove a layer when you see them.
For itching, Cleveland Clinic suggests a cool washcloth. Keep nails short: Cleveland Clinic warns that scratched, broken skin can become infected.
What Not to Put on Heat Rash
Most creams make heat rash worse by sealing the skin and blocking sweat ducts further.
Thick, greasy ointments: the AAP says directly not to apply thick greasy ointments to rash areas.
Creams and lotions: Cleveland Clinic and MedlinePlus advise avoiding them because they can block pores.
Powders: Cleveland Clinic warns that powders that seem soothing can block pores, and MedlinePlus cautions that infants can inhale powder.
Extra layers or a blanket: covering a rash to protect it traps more heat.
Cleveland Clinic says calamine lotion may help intense itching but advises checking with a provider or pharmacist first. For a baby, ask your pediatrician before using any medicated or anti-itch cream. If your baby also has diaper rash, see diaper rash vs yeast infection.
How Long Does Heat Rash Last?
Not long, once the heat is gone:
Source
What it says about timing
Cleveland Clinic
Heat rash usually clears within a few days once the skin is cooled and dried
StatPearls (NIH)
Miliaria crystallina typically resolves within 24 hours; most cases resolve on their own once the triggers are reduced
AAP (HealthyChildren.org)
Call the doctor if the rash has not improved after 3 days of home treatment or gets worse within 24 hours
How long heat rash lasts, by source.
Heat rash can return whenever your baby gets hot and sweaty, so a rash that keeps coming back is a sign to adjust layers or room temperature. Cleveland Clinic advises calling your pediatrician if rashes keep recurring or last more than a few days.
Heat Rash vs Other Baby Rashes
Several baby rashes look alike. Use this table as a starting point, not a diagnosis; a daylight photo can help your pediatrician.
Rash
What it looks like
Where
Clues
Heat rash
Tiny red bumps or clear blisters; gray or white on darker skin
Neck folds, upper chest and back, armpits, diaper area, hairline
Appears after warmth or sweating; fades when cooled
Baby acne
Red bumps, sometimes with white centers
Face
MedlinePlus says it usually starts at 2 to 4 weeks; not tied to heat. See baby acne
Eczema
Dry, scaly, red or darker, itchy patches that can thicken
Varies
Dry, scaly texture; often runs in families (MedlinePlus)
Hives
Raised red welts
Anywhere; they move around
Welts change size and shape and shift location (MedlinePlus)
Diaper rash
Red, irritated skin
Diaper area
From dampness and contact with urine or stool; a yeast rash is very red with small red bumps at the edges (MedlinePlus)
Often comes with fever or other signs of illness; a rash with fever needs a call (MedlinePlus). See roseola
Petechiae
Flat, pinpoint purple, red or brown dots
Anywhere
Do not fade when pressed; can signal a medical emergency, especially in children (Cleveland Clinic)
Heat rash compared with other common baby rashes. Sources: MedlinePlus, Rash: child under 2 years; Cleveland Clinic, Heat Rash and Petechiae; AAP, Heat Rash.
A simple way to check the last row: press gently on a spot. Cleveland Clinic explains that a typical rash turns pale or lighter when pressed, while petechiae stay purple, red or brown.
One more newborn rash, erythema toxicum: MedlinePlus describes flat red splotches, often with a white, pimple-like center, that affect up to half of babies and usually fade in 7 to 14 days without treatment.
Overheating, Safe Sleep and Preventing Heat Rash
Heat rash is a sign your baby has been too warm, and the AAP states in its safe sleep guidance that overheating can increase the risk of SIDS. Heat rash after naps or nights is a nudge to check how your baby is dressed for sleep.
Layers: the AAP’s general rule is to dress your baby in only one layer more than you are wearing. See how to dress baby for sleep and our TOG chart.
No loose blankets: the AAP advises only a fitted sheet in the crib; for warmth, add a clothing layer or a wearable blanket.
No hats indoors: the AAP says not to put a hat on your baby indoors once you are home from the hospital.
Back to sleep, on a flat, bare surface: heat rash never changes the basics: baby alone, on their back, on a firm, flat, bare surface.
Airflow: the AAP suggests air conditioning or a gently blowing fan on hot days and limiting time in hot places or a car seat. See baby room temperature for sleep.
Check the chest or back of the neck: if it feels hot or damp, or you see flushed skin, remove a layer. Our baby sweating while sleeping guide explains what is normal, and night sweats in children covers older kids.
Heat rash is usually mild, but some rashes need a doctor quickly. Call any time you are worried.
Call 911 or go to the emergency room right away if your baby:
Has trouble breathing, or is very hard to wake or unresponsive.
Has flat purple, red or brown pinpoint spots that do not fade when pressed, especially with fever, or spots that spread quickly. Cleveland Clinic says petechiae can be a sign of a severe illness or medical emergency, especially in children.
Call your pediatrician right away (day or night) if:
Your baby is younger than 3 months with a temperature of 100.4 F (38.0 C) or higher: the AAP says to call the doctor right away for any fever at this age.
The rash comes with a fever: the AAP lists fever as a reason to call about heat rash, and MedlinePlus lists a fever or other unexplained symptoms with a rash.
Your baby is younger than 3 months and has any new rash, spots or blisters: per MedlinePlus.
Your baby is eating less or is less active than usual: per the AAP.
Call the office during regular hours if:
The rash looks infected: tender, oozing, or draining pus, or the skin is warm and swollen (AAP, MedlinePlus, Cleveland Clinic).
It is not getting better: no improvement after 3 days of home treatment, or worse within 24 hours (AAP).
It keeps coming back: or lasts more than a few days (Cleveland Clinic).
Your baby is scratching a lot: or a diaper-area rash spreads beyond the diaper (MedlinePlus).
This article is general education, not medical advice, and cannot diagnose a rash.
Frequently Asked Questions
What does baby heat rash look like?
Baby heat rash looks like patches of tiny bumps, about 1 to 3 millimeters wide, or small clear blisters. Cleveland Clinic says the bumps look red on lighter skin and may look gray or white on darker skin. It usually appears in the neck folds, upper chest and back, armpits, diaper area or along the hairline.
How long does heat rash last on a baby?
Cleveland Clinic says heat rash usually clears within a few days once the skin is cooled and dried, and the mildest clear-blister type often fades within a day. The American Academy of Pediatrics advises calling your doctor if the rash has not improved after 3 days of home care or gets worse within 24 hours.
How do I get rid of heat rash on my baby fast?
Cool your baby down. Move to a cooler room, give a cool bath or use cool, moist washcloths, then pat the skin completely dry. Leave the rash uncovered when you can and dress your baby in thin, loose cotton. Avoid thick ointments, creams and powders, which can block sweat ducts and slow healing.
Can heat rash appear on a baby’s face?
Yes. The American Academy of Pediatrics says heat rash can occur almost anywhere, though it is most common in the neck folds, upper chest and back, hairline and diaper area. Because baby acne, eczema and drool rash also show up on the face, compare where and when the rash appears, and ask your pediatrician if you are unsure.
Does heat rash bother babies?
It can. Heat rash may feel itchy or prickly, so your baby may seem fussier or more wiggly than usual. The mildest type, with tiny clear bumps, often does not itch at all. Cool compresses and lighter clothing usually bring relief, and short nails help prevent scratches that could let infection in.
When should I worry about a heat rash on my baby?
Call your pediatrician right away if your baby is under 3 months with a temperature of 100.4 F or higher, has a rash with fever, is eating less or less active, or the rash has pus or tender, swollen skin. Flat purple or red spots that do not fade when pressed need emergency care.
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