Baby sweating in the sleeping bag? Here’s how to tell if it’s too warm
https://lillavilla.dk/blogs/tips-og-rad/baby-sveder-i-soveposen-er-den-for-varm
Short answer: If your baby is sweating in the sleep sack, they are probably too warm. Feel the chest, back, or neck: the skin should feel comfortably warm and dry – not hot, damp, or clammy. If the baby is warm or sweaty, remove a layer of clothing or choose a lighter sleep sack and check again after a little while.
Cold hands and feet do not necessarily mean that the baby is cold. They can feel cooler than the rest of the body, even when the temperature is suitable.
The Lullaby Trust recommends a room temperature of 16–20 °C as a general guideline and stresses that each child should be checked individually for signs of overheating. Also, always follow the temperature and use instructions for the specific sleep sack.
Why does a baby sweat in a sleep sack?
A baby may start sweating if the combination of room temperature, sleepwear, and sleep sack traps too much heat. This can happen, for example, when:
- the bedroom is warmer than usual
- the baby is wearing too many layers of clothing
- the sleep sack is too warm for the season or the room
- the child has a fever or is unwell
- the temperature changes during the night
Young children do not regulate their body temperature in the same way as adults. That is why it is important to check the child's temperature directly instead of judging it only by how the room feels to you.
How to tell if your baby is too warm
Gently feel the baby's chest, tummy, or neck. This gives a more accurate indication than the hands and feet.
Signs that the baby may be too warm include:
- a warm, damp, or sweaty neck
- a warm chest or back
- damp hair
- red or warm cheeks
- restlessness or frequent waking along with other signs of being too warm
If the baby feels warm or sweaty, you can remove one layer of clothing and check the temperature again after a little while. You can also choose a lighter sleep sack if the room is warm.
If the child has a fever, seems unusually lethargic, has trouble breathing, or otherwise seems unwell, you should contact a doctor or an out-of-hours medical service.
What is a suitable bedroom temperature?
The Lullaby Trust and the NHS recommend a room temperature of around 16–20 °C as a general guideline when a baby is sleeping. However, the clothing should always be adapted to the baby, the sleep sack, and the room temperature.
| Situation | What can you do? |
|---|---|
| The baby's neck is comfortably warm and dry | Keep the current clothing |
| The neck is warm, damp, or sweaty | Remove a layer or choose a lighter sleep sack |
| The chest feels cool | Add a light layer of clothing |
| The hands and feet are cool, but the chest is warm | It is often completely normal |
| The room gets warmer during the night | Use lighter sleepwear and check your baby’s neck |
A room thermometer can make it easier to choose sleepwear and a sleep sack. It is more accurate than guessing the temperature.
Should my baby wear less clothing under the sleep sack?
It depends on the room temperature, the sleep sack material, and the manufacturer’s instructions. A sleep sack usually replaces a duvet or other loose bedding, but your baby may still need a lightweight layer underneath.
On warm nights, a short-sleeved bodysuit or another lightweight layer may be enough. In cooler rooms, your baby may need more clothing or a warmer sleep sack.
It is best to start with a few lightweight layers that are easy to adjust. Always follow the temperature guidance for the specific sleep sack, as materials and warmth levels can vary between products.
Can sweating cause a baby to wake up?
Yes, a baby who is too warm may become restless and wake more often. But warmth is just one of many possible explanations for waking during the night. Hunger, development, teething, illness, a wet diaper, and the need for closeness may also play a role.
If your baby often wakes with a damp neck or wet hair, try a lighter layer of clothing or a thinner sleep sack and see if they seem more comfortable.
Sleep sacks on warm summer nights
On warm nights, ventilation and lightweight materials are important. Keep the room as comfortable as possible, and avoid placing the crib in direct sunlight or near a heat source.
The Danish Health Authority also recommends not covering a stroller with a muslin cloth or blanket in warm weather. A covered opening can restrict airflow and cause the temperature inside the stroller to rise sharply.
If your baby sleeps outdoors, keep the stroller in the shade throughout their sleep and check on them regularly.
How to reduce the risk of overheating
- Use a room thermometer.
- Feel your baby’s chest or neck, not just their hands.
- Adjust your baby’s clothing to the room temperature.
- Follow the sleep sack manufacturer’s temperature guidance.
- Avoid putting a hat on your baby indoors while they sleep.
- Do not place the crib near a radiator, heater, or in direct sunlight.
- Do not use a duvet or extra blankets on top of the sleep sack.
- Check your baby’s temperature again if the weather or room temperature changes.
Frequently asked questions
Is it normal for a baby to sweat around the neck?
A little moisture can be normal, but a warm, sweaty neck may be a sign that your baby is wearing too many clothes or that the sleep sack is too warm. Remove a layer and check the temperature again.
How do I know if my baby is cold?
Feel their chest or neck. If their chest feels cool, the child may need an extra lightweight layer. Cold hands and feet are not in themselves a reliable sign that the baby is cold.
Can a baby sleep with a hat?
As a rule, babies should not sleep with a hat indoors. The head helps the child release heat, and a hat can increase the risk of overheating.
Should a duvet be used with a sleep sack?
A baby sleep sack is generally intended to replace a duvet and other loose bedding. Always follow the manufacturer's instructions, and avoid adding extra blankets on top of the sleep sack.
Which sleep sack should I choose for a warm bedroom?
Choose a lightweight, well-fitting sleep sack that suits the current room temperature. Check the product's temperature or TOG guidance, as warmth levels vary from one model to another.
In short
If your baby sweats in the sleep sack, feel their chest or neck. A warm, damp, or clammy neck suggests the child is too hot. Remove a layer of clothing or choose a lighter sleep sack, and check the temperature again.
Use the room temperature and the manufacturer's instructions as a starting point, but always assess your individual child. The baby's chest and neck provide the best practical indication of whether the temperature is appropriate.
Sources
- Danish Health Authority: Preventing sudden infant death
- Danish Health Authority: Hot weather
- NHS: Safe sleep advice for babies
- The Lullaby Trust: Room temperature
Also read our guides on baby sleep and sleep sacks
Unsure how much clothing your baby should wear under a sleep sack? Read our guide to what babies should wear in a sleep sack, where we cover temperature and layers.
If your child wakes several times during the night, you can also read about why babies often wake up at night, and how temperature, clothing, and sleep sacks can affect sleep.
When temperatures rise, find practical tips in our guide to summer sleep sacks for babies and warm nights.
More practical guides about sleep sacks
If you'd like to read more tips about baby sleep and sleep sacks, continue to our practical guides or browse our selection of sleep sacks for babies and children.
If you're unsure whether the sleep sack is suitable for the season, read our guide on whether babies can use a sleep sack all year round. If you're interested in flexible styles, you can also read about when a sleep sack with removable sleeves makes sense.