Why Your Baby Overheats at Night - and How to Stop It
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Written by Kayal, founder of PassifloraKidz · September 2026
If you’ve picked your baby up in the morning and found damp hair stuck to a hot little forehead, you’re in the right place. Night-time overheating is common, it’s fixable, and it’s worth taking seriously — getting too warm in sleep is one of the risk factors safe-sleep organisations ask parents to manage. Here’s what causes it and what actually helps.
This article follows guidance from The Lullaby Trust and the American Academy of Pediatrics. It’s general information, not medical advice — if your baby is unwell, feverish, or you’re worried, call your doctor.
Signs your baby is too warm
Babies can’t kick off a blanket or tell you they’re hot, and they regulate temperature less well than adults — they have more skin surface for their size, so they heat up and cool down faster. Watch for:
- sweating, damp hair, or a clammy neck and back
- flushed or red cheeks
- rapid breathing
- heat rash — small red or prickly bumps, often on the neck, chest or in skin folds
- restless, broken sleep, or waking hot and unsettled
How to check properly: feel the chest, tummy or the back of the neck — not the hands and feet. A baby’s hands and feet are almost always cooler and slightly bluish; that’s normal and not a sign they’re cold. If the chest feels hot or sweaty, remove a layer.
The safe room temperature range
There isn’t one universal number, and the two most-cited authorities differ slightly:
- The Lullaby Trust (UK): aim for 16–20°C (about 61–68°F), and note that many homes will be warmer than this, especially in summer.
- US pediatric guidance (AAP-aligned): commonly cited as 68–72°F (20–22°C).
Put together, a practical target is roughly 18–21°C / 65–70°F. A cheap room thermometer (many video monitors have one built in) takes the guesswork out. If you can’t get the room cool enough in hot weather, follow “summer rules”: lighter clothing and bedding, a fan moving air around the room but not aimed at the baby, blackout blinds during the day, and the door open.
Why fabric matters more than parents expect
Your baby wears one garment for 10–12 hours across the warmest part of their day, often under a sleep sack. What that garment is made of changes how much heat and moisture it traps:
- Polyester fleece sleepwear and blankets are the most common overheating culprit — fleece insulates well and doesn’t release heat or absorb sweat, so it sits warm and damp.
- Cotton breathes but holds moisture; a sweated-through cotton onesie stays wet against the skin.
- Bamboo lyocell and fine merino are the most temperature-regulating: they breathe, move moisture outward, and dry faster, so a hot sleeper is less likely to wake up soaked.
Overheating and eczema often travel together, too — heat and trapped sweat are classic itch triggers. If that’s your situation, our companion guide on the best pajamas for babies with eczema goes deeper on fabric.
TOG and layering, made simple
TOG is just a measure of warmth. Sleep sacks are rated so you can match them to the room:
| Room temperature | Sleep sack TOG | Under the sack |
|---|---|---|
| 24–27°C / 75–81°F | 0.5 TOG or just clothing | Short-sleeve bodysuit |
| 20–24°C / 68–75°F | 1.0 TOG | Long-sleeve pajamas or bodysuit |
| 16–20°C / 61–68°F | 2.5 TOG | Long-sleeve pajamas |
| Below 16°C / 61°F | 3.5 TOG | Long-sleeve pajamas ± a vest |
Two rules that keep you out of trouble:
- Dress your baby in one more layer than you’d wear to be comfortable in the same room — no more.
- No hats indoors for sleep, and no loose blankets for under-1s. Babies lose excess heat through the head and face; covering it removes their main way to cool down.
A breathable base layer does a lot of the work here. Our bamboo two-piece pajama set and Zippy Romper are both single-layer 230 GSM bamboo lyocell, designed to pair with a sleep sack without adding bulk.
How bamboo lyocell helps with temperature
I started PassifloraKidz because heat was my own son’s worst night-time trigger, and bamboo lyocell was the fabric that helped most. It breathes, it wicks moisture off the skin instead of holding it, and it doesn’t have the “greenhouse” effect fleece does. It won’t fix a room that’s 26°C — nothing worn will — but within a sensible range it widens the band of comfortable.
The same logic applies to what they cuddle: our Signature Bamboo Blanket is deliberately lightweight for supervised, awake use rather than a thick fleece throw. You can see the full range of single-layer bamboo sleepwear in our bamboo baby & toddler collection.
Quick checklist for a cooler night
- Room at roughly 18–21°C / 65–70°F; check with a thermometer
- Match sleep sack TOG to the room; one layer more than you’d wear, no more
- Single-layer, breathable pajamas — bamboo lyocell, merino or cotton, not fleece
- No hat, no loose blanket, no cot bumpers or pillows
- Move the cot away from radiators and direct sun; close blinds during the day in summer
- Check the chest or back of the neck, not hands and feet
- If your baby is sweating through a correctly-dressed night, cool the room further before adding fans or changing routine
- Call your doctor for a fever, or if a baby is hot, floppy, or hard to wake
Frequently asked questions
What room temperature stops a baby overheating at night?
Aim for roughly 18–21°C (65–70°F). The Lullaby Trust recommends 16–20°C; US pediatric guidance is often cited as 68–72°F. Use a thermometer and dress your baby for the actual room temperature.
Why does my baby’s head sweat so much when sleeping?
Babies release excess heat through the head and face, so a sweaty head often means the body is slightly too warm or the sleepwear is trapping heat. Remove a layer, switch fleece for a breathable fabric, and never put a hat on a sleeping baby indoors.
Is it better for a baby to be too hot or too cold?
Slightly cool is safer than too warm. Overheating is a recognised risk factor for SIDS, while a slightly cool baby will usually just wake. Dress for the room and check the chest rather than the hands.
Can pajama fabric really cause overheating?
Fabric doesn’t create heat, but it changes how much is trapped. Polyester fleece insulates and holds sweat; bamboo lyocell, merino and cotton breathe and release moisture. For a hot sleeper, switching fabric can make a noticeable difference.
Should I use a fan in my baby’s room?
A fan is fine and some research links air circulation to lower SIDS risk. Don’t point it directly at the baby; aim it at a wall to move air around the room.
About the author. I’m Kayal, founder of PassifloraKidz. I make bamboo lyocell sleepwear and started the brand after my own son’s heat-triggered eczema and broken nights. I’m a parent, not a medical professional — the safety points here are drawn from The Lullaby Trust and the AAP, and anything about your own child should go to your doctor or health visitor.