Signs of Overheating in Babies: SIDS Risk and How to Keep Baby Cool

Keeping a baby at the right temperature is one of those things that sounds straightforward but causes genuine anxiety for many parents, particularly in the early weeks. Overheating in sleeping babies is a recognised risk factor for Sudden Infant Death Syndrome (SIDS), and knowing the signs of an overheated baby — and how to prevent overheating — is important knowledge for every parent.

Why Overheating Is a SIDS Risk Factor

The link between overheating and SIDS has been established through epidemiological research since the 1990s. While the exact mechanism is not fully understood, current evidence suggests that:

• Overheating may affect the normal arousal responses in babies during sleep
• High body temperature can alter breathing control in the developing brainstem
• The risk is greatest in the first six months of life, when SIDS incidence is highest

The Lullaby Trust, which provides evidence-based safe sleep guidance in the UK, identifies overheating as one of the key modifiable risk factors alongside sleeping position and tobacco smoke exposure.

How to Tell If Your Baby Is Too Hot

Babies cannot tell you they are hot and cannot remove their own clothing. Parents need to know the signs.

The back of the neck or tummy test: This is the most reliable way to check your baby's temperature. Place the back of your hand on your baby's tummy or the nape of their neck. The skin should feel warm but not hot or sweaty. Hands and feet are not a reliable guide — they are naturally cooler than the rest of the body and can feel cold even when a baby is too warm overall.

Signs your baby may be overheating:

• Skin that feels hot and sweaty, particularly on the back, tummy, or neck
• A flushed or red face
• Rapid breathing (faster than their normal rate)
• Unsettled behaviour, restlessness during sleep, or unusual fussiness
• Damp hair
• Heat rash (see our heat rash guide)

Signs of severe overheating or heat exhaustion in a baby (seek urgent medical help):

• Very high temperature (above 38°C in babies under three months, above 39°C in older babies) without obvious illness
• Limpness or unusual lethargy
• Difficulty rousing or unusual unresponsiveness
• Rapid heartbeat

Room Temperature Guidance

The recommended room temperature for a baby to sleep is 16–20°C, with around 18°C often cited as ideal. This applies to the room in which the baby sleeps, not the whole house.

A room thermometer is a worthwhile investment — our perception of room temperature is unreliable, particularly at night. Many baby monitors include room temperature readings.

In summer, keeping rooms cool can be challenging. Strategies include:

• Opening windows in the early morning and closing them and curtains/blinds before the day heats up
• Using a fan to circulate air (not directed at the baby, but circulating the air in the room)
• Moving your baby's sleeping space to the coolest room in the house if necessary

Safe Layering for Different Seasons

The TOG system (Thermal Overall Grade) is commonly used for baby sleeping bags and sleep suits, and understanding it helps with layering decisions. See our dedicated guide to newborn temperature regulation for a full explanation of TOGs.

General seasonal guidance (assuming room temperature is 16–20°C):

Summer (room 24°C or above): Nappy and light vest only, or a very low TOG sleeping bag (0.5 TOG) with no additional layers. Do not swaddle in hot weather.

Spring/Autumn (room 18–22°C): Light sleepsuit with a 1.0 TOG sleeping bag, or just a sleepsuit. A lightweight swaddle blanket if swaddling.

Winter (room 16–18°C): Sleepsuit with a 2.5 TOG sleeping bag, or sleepsuit with a light blanket (tucked securely so it cannot cover the face).

These are general guidelines and need to be adjusted based on your specific room temperature and your individual baby.

What Not to Do

• Do not add a hat indoors: A hat prevents heat from escaping through the head, which can cause a baby to overheat rapidly. Hats are only for outdoors in cold weather, not for sleep.
• Do not use a duvet or pillow until at least 12 months: These are not suitable for babies and create overheating and suffocation risks.
• Do not wrap the pram or buggy in blankets: Draping a blanket over a pram can significantly increase the temperature inside it. Use a proper pram parasol or sun canopy instead, and leave a ventilation gap.
• Do not put a baby in a car seat with a thick snowsuit: A thick snowsuit compresses the harness straps in a crash and creates significant overheating risk during drives. Instead, use a thin sleepsuit and place a blanket over the harness straps.
• Do not use electric blankets or heat pads: These are not safe for baby sleep.

In Hot Weather

In a heatwave, keeping a baby cool requires active management:

• Keep the sleeping room as cool as possible using the strategies above
• Offer extra feeds (breastfed babies need more frequent feeding; formula-fed babies over six months can have small amounts of cooled boiled water)
• Dress babies minimally — a vest or even just a nappy in very hot weather
• Never leave a baby in a parked car, even for a few minutes

Regular checks on your baby during the night are always worthwhile when temperatures are unusually high.