Baby Heat Rash (Prickly Heat / Miliaria)
The short answer
Heat rash happens when sweat gets trapped under your baby's skin, causing tiny red bumps or blisters, usually in skin folds or areas covered by clothing. It is harmless and clears up quickly once your baby is cooled down. Dressing your baby in one layer more than you would wear is a good rule of thumb to prevent overheating.
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By Age
What to expect by age
0-3 months
Newborns are especially prone to heat rash because their sweat glands are not fully developed. It often appears on the neck, chest, groin folds, and armpits. Well-meaning parents sometimes overdress newborns, which is a very common cause. A good guide is to dress your baby in one more layer than you are comfortable in.
3-6 months
Heat rash commonly appears in the folds of the neck where drool and sweat collect, and in the creases of chubby arms and legs. In warm weather, choose loose, breathable cotton clothing and keep indoor temperatures comfortable. A lukewarm bath can provide quick relief from a heat rash flare.
6-12 months
As babies become more active and mobile, they generate more body heat. Heat rash may appear after active play, being in a car seat for an extended period, or wearing a carrier. Removing layers, moving to a cooler environment, and allowing air to reach the affected skin usually resolves it within hours.
12 months+
Toddlers are busy and active, making heat rash during warm months fairly common. It is especially likely in the diaper area, behind the knees, and in elbow creases. As your child's sweat glands mature, heat rash tends to become less frequent. Keeping them hydrated and dressed in breathable fabrics helps.
What Should You Do?
When to take action
- Tiny red bumps in skin folds, on the neck, or under clothing that appear during warm weather or after overdressing
- The rash clears up within a few hours to a day once your baby cools down
- Small clear or white blisters on the skin surface that do not seem to bother your baby
- Rash that comes and goes with temperature and clothing changes
- The heat rash does not improve within 2-3 days even after keeping your baby cool and dry
- The bumps seem to be getting larger, more red, or more swollen
- Your baby is scratching intensely at the rash or seems unusually fussy
- The rash develops pus-filled bumps, red streaks, or warm swollen areas, which may indicate a secondary infection
- Your baby has a fever along with a rash and seems unwell, as this may indicate a different type of rash that needs evaluation
Sources
Related Resources
Trust your instincts. If something feels wrong, reach out to your pediatrician.
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Related Skin Concerns
Baby Rash in Skin Folds - Neck, Armpits, and Creases
Rashes in baby's skin folds (neck, armpits, groin, behind ears, elbow and knee creases) are extremely common because these warm, moist areas trap moisture from drool, spit-up, sweat, and milk. The medical term is intertrigo. Most fold rashes respond to keeping the area clean and dry. If the rash is bright red, has satellite spots, or has a yeasty smell, it may have developed a yeast (candida) infection and need antifungal treatment. Keeping folds dry is both the treatment and prevention.
Baby Chin Rash from Drooling
Drool rash is extremely common and appears as red, irritated, or slightly bumpy skin on the chin, cheeks, neck, and chest where drool sits. It is caused by the constant moisture and digestive enzymes in saliva irritating the skin. Keeping the area dry and applying a barrier like petroleum jelly before drool exposure is the most effective treatment.
Baby Rash Around the Mouth - Drool Rash and Other Causes
A rash around your baby's mouth is most commonly drool rash (contact irritant dermatitis from constant moisture). Drool rash looks like red, slightly rough, chapped skin around the mouth, chin, and cheeks. It is very common during teething when drool production increases dramatically. Other causes include food contact irritation (especially from acidic foods like tomato and citrus), pacifier friction, eczema, and occasionally hand-foot-and-mouth disease. True food allergies typically cause hives or swelling, not a flat red rash.
Raised Bumps on Baby's Skin
Raised bumps on a baby's skin have many possible causes, most of which are harmless. Common causes include keratosis pilaris (tiny rough bumps on upper arms and thighs), molluscum contagiosum (small, dome-shaped, pearl-like bumps from a viral infection), insect bites, viral rashes, and milia (tiny white bumps in newborns). The bumps' appearance - their color, size, texture, location, and whether they are itchy - helps determine the cause. Most resolve on their own or with simple treatment.
Baby Rash That Won't Go Away
A rash that persists for more than 2 weeks or keeps recurring likely needs evaluation beyond "wait and see." The most common causes of persistent rashes in babies include eczema (dry, itchy, patches), fungal infections (especially in skin folds), contact dermatitis (reaction to a product), and less commonly, psoriasis or autoimmune conditions. Proper identification is important because the treatment differs significantly - using the wrong cream (like steroid cream on a fungal infection) can actually make things worse.
Baby Eczema (Atopic Dermatitis)
Baby eczema is extremely common, affecting up to 20% of infants, and is not caused by anything you did wrong. It shows up as dry, red, itchy patches and is very manageable with consistent moisturizing and gentle skin care. Most children outgrow it by school age.