Your baby has developed small red spots on the neck, in the skin folds, or on the back. It's been warm outside — or perhaps they've been bundled up a little too well. Could it be heat rash?
Heat rash (miliaria) is extremely common in babies and young children. It's completely harmless but can be uncomfortable for your little one. Here's what heat rash is, how to prevent it, and how to tell it apart from other rashes.
What is heat rash?
Heat rash occurs when sweat glands become blocked and sweat can't reach the surface of the skin. Instead, it gets trapped beneath the skin and forms small blisters or bumps.
Babies are especially prone to heat rash because:
- Sweat glands are immature — they're not fully developed during the first few years of life
- Skin is thinner and sweat ducts narrower than in adults
- Babies can't communicate that they're too warm
- They're often overdressed by well-meaning parents
Heat rash can appear year-round — not just in summer. Anything that makes a baby too warm can trigger it: too many layers of clothing, a warm room, a fever, or close carrying in a baby carrier.
What does heat rash look like?
There are three types of heat rash, ranging from mild to more pronounced:
1. Miliaria crystallina (the mildest form)
- Small, clear blisters that look like tiny water droplets on the skin
- The blisters are not red or inflamed
- No itching or discomfort
- Disappears quickly (within hours to a couple of days) once the child cools down
- Most common in newborns
2. Miliaria rubra (the most common form)
- Small red spots or bumps in the skin
- Can cause itching and irritation — the child may be unsettled
- Skin around the spots looks red and irritated
- Most common in skin folds — neck, armpits, groin, inside of the elbows, behind the ears
- Can also appear on the back, chest, and diaper area
- Develops over hours to days
3. Miliaria profunda (the rarest form)
- Deeper, skin-colored bumps under the surface
- Less redness than miliaria rubra
- Very uncommon in babies
- Occurs after repeated episodes of heat rash
The most common type in babies is miliaria rubra — the characteristic small red spots appearing in skin folds and in areas that are warm and moist.
Where does heat rash appear?
Heat rash typically shows up where the skin is warm, moist, or covered by clothing:
- Neck and nape — especially in the folds
- Armpits and inside the elbows
- Groin and diaper area
- Behind the ears
- Under the chin — particularly in babies with chubby necks
- Back and chest — where clothing sits close
- Forehead — under a hat
- Under a baby carrier — where baby is pressed against the parent
Treating heat rash
Heat rash is self-limiting and usually clears up on its own once the child cools down. Here's what you can do:
Cool your baby down
- Remove excess clothing — strip off a layer or two
- Move to a cooler environment — shade, or an air-conditioned room
- A lukewarm bath — a short, lukewarm bath can help cool the skin
- Let the skin breathe — allow baby to lie in just a diaper or light clothing
- A cool, damp cloth — gently place it over the affected area
Avoid further irritation
- Avoid thick creams or ointments — these can block sweat glands further
- Choose fragrance-free moisturizer if the skin is dry
- Don't rub or scrub the affected area
- Keep nails trimmed to prevent scratching
Clothing and fabrics
- Choose loose, light clothing in cotton or linen
- Avoid synthetic materials like polyester and nylon
- Use soft, breathable bedding
- Consider a thinner diaper if possible during heat spells
Dressing rule of thumb: Your baby needs roughly the same number of layers as you — plus one extra. In the heat, it's better to err on the side of slightly less than too much. Check whether your baby is warm by feeling the chest or neck — the hands and feet are often cool even when baby is comfortably warm.
Preventing heat rash
The best approach is to prevent your baby from getting too hot in the first place:
Clothing
- Dress baby for the actual temperature — not what season it is on the calendar
- One layer more than yourself is the general rule for newborns
- In warm weather: A light onesie or just a diaper indoors
- Cotton next to skin — breathable fabric that allows sweat to escape
- Check for overheating by feeling the chest or neck, not the hands
Indoors
- Keep room temperature comfortable — ideally 64–72°F (18–22°C) for the bedroom
- Good ventilation — open windows or use a fan (not aimed directly at baby)
- Don't bundle baby in heavy blankets or quilts
Outdoors
- Stay in the shade — avoid direct sun, especially between 10am and 3pm
- A light sun hat — protects the head without causing overheating
- Baby carrier in the heat — be aware that carriers can make both you and baby very warm. Consider a stroller with good ventilation instead
- Cars in summer heat — parked cars heat up extremely quickly. Check the car seat temperature before placing your baby in it
During breastfeeding
- Place a light, soft cloth between you and baby while nursing in warm weather
- Skin-to-skin contact generates a lot of heat — keep the area around you well ventilated
Never let baby sleep in direct sunlight. Babies under 6 months should avoid direct sun entirely. Use shade, a stroller sun cover, and lightweight clothing for protection.
Heat rash vs. other rashes
Babies can develop many different types of rashes, and it can be hard to tell them apart. Here's a quick comparison:
Heat rash vs. diaper rash
- Heat rash: Small spots; can appear anywhere that's warm
- Diaper rash: Red, irritated skin in the diaper area caused by moisture and friction
Heat rash vs. eczema (atopic dermatitis)
- Heat rash: Small red spots that disappear when the baby cools down
- Eczema: Dry, flaky, red skin that itches and is chronic or recurring
Heat rash vs. roseola
- Heat rash: Triggered by heat, limited to warm areas, clears with cooling
- Roseola: A rash that appears after a fever, spreading across the whole body
Heat rash vs. allergic reaction
- Heat rash: Small, uniform spots in skin folds, related to heat
- Allergic reaction: Can produce hives (urticaria), swelling, may appear anywhere
When should you see a doctor?
Heat rash is harmless and usually doesn't require a doctor's visit. Contact your pediatrician if:
- The rash doesn't clear up after 2–3 days of cooling measures
- Your child has a fever in addition to the rash (may indicate another cause)
- The rash looks infected — increased redness, swelling, pus, or weeping
- Your child seems unwell — lethargic, poor appetite, very unsettled
- The rash spreads rapidly across the whole body
- You're unsure what the rash is
If the heat rash develops yellow crusting, pus, or increased warmth in the skin, it may have become secondarily infected with bacteria. See your doctor for assessment and possible treatment.
Signs of overheating
Heat rash is usually a mild sign that your baby is too warm. More serious overheating requires prompt action:
- Red, hot skin across the whole body
- Rapid breathing
- Lethargy, drowsiness, or irritability
- Fast pulse
- Dry lips and reduced urine output (signs of dehydration)
Call emergency services if your child shows signs of serious overheating (heatstroke).
Frequently asked questions
Can newborns get heat rash?
Yes — newborns are especially prone because their sweat glands are immature. Many newborns develop miliaria crystallina (the mild, clear blisters) in their first few weeks, particularly if they're bundled up well.
Is heat rash contagious?
No. Heat rash is not contagious. It's caused by blocked sweat glands and has nothing to do with infection.
How long does heat rash last?
Mild heat rash (miliaria crystallina) often clears within hours of cooling down. Miliaria rubra can last 2–3 days. If the child continues to get too warm, the rash may persist.
Can I use cream on heat rash?
Generally, avoid thick creams and ointments as they can block sweat glands further. A light, fragrance-free moisturizer can be used if the skin is dry. Calamine lotion may help soothe itching — check with your pediatrician or pharmacist first.
Can heat rash occur in winter?
Yes — heat rash can appear year-round. A warm indoor environment, too many clothing layers, heavy blankets, and fever can all cause heat rash even in the colder months.