Overheating is an independent SIDS risk factor. Here's the ideal room temperature, how to spot an overheated baby, and how to use TOG ratings to dress your baby right for sleep.
Overheating is an independent risk factor for SIDS — not a minor footnote, but a standalone entry in the evidence base.1 Getting room temperature right and dressing your baby appropriately for sleep is one of the practical things families can control on every single night.
The target room temperature
The Lullaby Trust and the NHS both recommend keeping the baby's room at 16–20°C (60–68°F).23 This range might feel cool to adults, especially in winter, but it is the right environment for a sleeping infant.
Babies cannot regulate body temperature as efficiently as adults. They lose heat through their heads and cannot remove bedding if they become too warm. A room that feels comfortably warm to you may be dangerously warm for a swaddled or wrapped baby.
A room thermometer in the baby's sleep space is worth having — it takes the guesswork out. Place it away from radiators, windows, and direct sunlight for an accurate reading.
Signs your baby is too warm
Check for overheating by placing a hand on your baby's chest or back of the neck — not the hands or feet, which are normally cooler in young infants and aren't reliable indicators of core temperature.
Signs of overheating:
- Sweating on the neck or back
- Flushed or red face
- Rapid or laboured breathing
- Damp hair
- Feels hot to the touch at the chest
If your baby is overheated, remove a layer and allow the room to cool. Do not use fans blowing directly on a baby. Do not use cold water or ice.
Never put a hat on a sleeping baby indoors. Babies lose heat through their heads — this is a normal and necessary mechanism. A hat during indoor sleep can prevent heat loss and contribute to overheating.
What TOG actually measures
TOG is a measure of thermal resistance — how much a material insulates. A higher TOG means more insulation and more warmth retained. The scale is used across European bedding and is how sleep sack manufacturers describe the warmth of their products.
It is not a quality rating or a safety rating. It is purely a measure of insulating capacity. A 0.5 TOG sleep sack and a 2.5 TOG sleep sack are both safe — the difference is how warm they keep your baby.
TOG ratings by room temperature
The standard guidance from the Lullaby Trust and major sleep sack manufacturers:2
| Room temperature | TOG rating | What to wear underneath |
|---|---|---|
| 27°C+ (81°F+) | Nappy only or 0.5 TOG | Nappy only |
| 24–26°C (75–79°F) | 0.5 TOG | Short-sleeve vest |
| 21–23°C (70–73°F) | 1.0 TOG | Short-sleeve vest |
| 18–20°C (64–68°F) | 2.5 TOG | Long-sleeve vest |
| 16–17°C (61–63°F) | 2.5 TOG | Long-sleeve vest + sleepsuit |
| Below 16°C (below 61°F) | 3.5 TOG | Long-sleeve vest + sleepsuit |
The practical rule for most UK homes in winter: a room at 16–20°C with a 2.5 TOG sleep sack and a single long-sleeve vest underneath is the correct baseline. Don't add extra layers — the TOG system accounts for them.
The "one more layer" rule — and when it misleads
You may have heard that babies need "one more layer than you're wearing." This is a rough guide intended for the daytime, when adults are moving around and generating body heat. During sleep, adults are also relatively still and may actually wear the same amount of layering as a baby.
The TOG system is more reliable than the "one more layer" rule for sleep specifically, because:
- It accounts for the insulating power of the sleep sack itself
- It gives a specific recommendation for room temperature, not adult clothing
- It avoids cumulative over-layering when parents are already warmly dressed
If you're using a TOG-rated sleep sack, follow the temperature table, not the layer rule.
Sleep sacks vs loose blankets
For the first 12 months, sleep sacks are strongly preferred over loose blankets.13 A fitted sleep sack cannot migrate over the face, cannot be kicked off, and cannot bunch up. These properties matter:
- A loose blanket that covers the face creates rebreathing risk
- A kicked-off blanket means a cold, waking baby at 3am
- Neither problem applies to a properly fitted sleep sack
Choose a sleep sack with a tog appropriate for your room. The correct sleep sack, in the correct size, with appropriate clothing underneath, is the complete solution for infant warmth during sleep.
Second-hand sleep sacks
Second-hand sleep sacks are generally fine. Unlike mattresses, where the advice is to use a new one (due to concerns about bacterial buildup in used foam), a clean sleep sack with no damage, intact zips, and no significant wear is safe to use. Check the tog label before use, especially if the label is faded.
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Also in this cluster: What to put in the cot · Swaddling: how to do it safely and when to stop
Sources
- American Academy of Pediatrics. "Sleep-Related Infant Deaths: Updated 2022 Recommendations for Reducing Infant Deaths in the Sleep Environment." Pediatrics 150(1), 2022. https://publications.aap.org/pediatrics/article/150/1/e2022057990/188304/Sleep-Related-Infant-Deaths-Updated-2022-Recommendations
- The Lullaby Trust. "What room temperature should a baby sleep in?" 2024. https://www.lullabytrust.org.uk/safer-sleep-advice/baby-room-temperature/
- NHS. "Reduce the Risk of Sudden Infant Death Syndrome (SIDS)." NHS, 2024. https://www.nhs.uk/conditions/baby/caring-for-a-newborn/reduce-the-risk-of-sudden-infant-death-syndrome/
Footnotes
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American Academy of Pediatrics. "Sleep-Related Infant Deaths: Updated 2022 Recommendations for Reducing Infant Deaths in the Sleep Environment." Pediatrics 150(1), 2022. https://publications.aap.org/pediatrics/article/150/1/e2022057990/188304/Sleep-Related-Infant-Deaths-Updated-2022-Recommendations ↩ ↩2
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The Lullaby Trust. "What room temperature should a baby sleep in?" 2024. https://www.lullabytrust.org.uk/safer-sleep-advice/baby-room-temperature/ ↩ ↩2
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NHS. "Reduce the Risk of Sudden Infant Death Syndrome (SIDS)." NHS, 2024. https://www.nhs.uk/conditions/baby/caring-for-a-newborn/reduce-the-risk-of-sudden-infant-death-syndrome/ ↩ ↩2