Room temperature and how to dress a baby for sleep are among the most common practical questions parents ask midwives and health visitors. They are also questions with a specific clinical relevance: overheating is a recognised risk factor for sudden infant death syndrome (SIDS). Getting this right matters, and it is more straightforward than the variety of products and TOG ratings on the market might suggest.
Healthbooq (healthbooq.com/apps/healthbooq-kids) covers safe infant sleep and newborn care.
Why Overheating Matters for SIDS
The association between overheating and SIDS has been established in epidemiological research over several decades. Peter Fleming at the University of Bristol, whose CESDI SUDI studies and Bristol SIDS research programme have contributed more to UK understanding of SIDS risk factors than almost any other research group, documented that overwrapping and excessive bedding were significantly associated with SIDS risk, particularly in the context of minor illness (which itself raises body temperature).
The Lullaby Trust, which coordinates UK SIDS prevention guidance, recommends a room temperature of 16-20°C for infant sleep, with 18°C as the optimal target. In hot weather or warm rooms, this may require active cooling (a fan, not directed at the baby), or reducing clothing and bedding layers.
The mechanism is not fully understood, but one hypothesis involves arousal from sleep: a baby who is too warm may have difficulty arousing from deep sleep – and reduced arousal responsiveness is a consistent feature of SIDS cases in post-mortem physiological research.
Checking for Overheating
A common parental error is checking the baby's hands or feet to assess temperature. The hands and feet of babies are frequently cool even when the core body is warm – this is normal peripheral vasoconstriction that is part of infant thermoregulation. A baby with cold hands may be quite warm centrally.
The Lullaby Trust advises checking the baby's neck or the back of the head to assess temperature. The skin in these areas reflects core body temperature more accurately. A neck or chest that feels hot and sweaty indicates overheating; a neck that feels warm and comfortable is appropriate.
Signs of overheating: flushed face, sweating (the hair may appear damp at the nape of the neck), rapid breathing, unusually restless sleep, and a body temperature above 37.5°C on a thermometer.
Signs of being too cold: cool neck/chest skin, skin that feels mottled or pale, and unusual restlessness or fussiness.
Appropriate Dressing: The TOG System
The TOG (Thermal Overall Grade) system rates the thermal insulation of infant sleeping bags and some other infant bedding. A higher TOG number indicates more insulation. The dressing guide published by the Lullaby Trust and most infant sleeping bag manufacturers provides a layering framework by room temperature and TOG rating:
At 16-20°C (most UK homes in winter), a 2.5 TOG sleeping bag with a babygrow (sleepsuit) is generally appropriate. At 20-24°C (a warm room or summer), a 1 TOG sleeping bag with just a nappy or vest and nappy. Above 24°C, a very thin 0.5 TOG bag or just a sheet, often with minimal clothing. In hot weather above 25-26°C, just a nappy may be sufficient.
These are guides, not rigid rules; individual babies have different metabolic rates and thermoregulatory preferences, and adjusting based on the neck temperature check is the most reliable approach.
Loose Bedding
Loose bedding in the cot – duvets, quilts, pillows, cot bumpers, and positioners – should not be used for babies under 12 months. The risks are both suffocation (loose fabric can cover the face) and overheating. A firm, flat mattress with a well-fitted sheet, and a sleeping bag rather than blankets, is the recommended sleep environment. If blankets are used, they should be firmly tucked in at the level of the chest with the baby's arms above the tuck, and made of a lightweight material.
Key Takeaways
The recommended room temperature for infant sleep is 16-20°C, with 18°C considered optimal by the Lullaby Trust. Overheating is a risk factor for SIDS, and studies show that SIDS rates increase with high ambient temperatures and excess bedding. The key principle for dressing an infant for sleep is to layer appropriately for the room temperature using the tog rating of any sleeping bag. A baby's neck or back of the head (not the hands, which are often cooler) is the best place to check for overheating. Loose bedding, including duvets, pillows, and cot bumpers, should not be used for infants under 12 months.
