Why does temperature matter?
Body temperature and sleep are intimately connected. When you begin to fall asleep, your body actively lowers its core temperature by approximately 1–2°C. This thermal drop is a biological signal that tells the brain it is time to rest.
If the room is too warm, your body cannot lower its temperature properly and sleep becomes more shallow. If it is too cold, the body spends energy staying warm instead of resting. Thermal balance is key to entering and maintaining deep sleep stages.
The ideal temperature according to science
Most sleep studies agree that the optimal temperature for sleeping is between 16 and 19°C. This range facilitates the body's natural thermoregulation and promotes more complete and restorative sleep cycles.
Below 15°C
Too cold. The body tenses to generate heat, making relaxation difficult.
16–19°C ✓
Optimal range. The body can regulate its temperature effortlessly and deep sleep is maximized.
20–23°C
Acceptable for many people. REM sleep may be slightly reduced.
Above 24°C
Too warm. Nighttime awakenings increase and deep sleep is reduced.
Keep in mind that these are averages. Older adults often prefer slightly warmer environments (18–21°C), while young children may need a slightly higher temperature (also 18–21°C, but with more bedding).
Temperature and sleep stages
Heat affects each sleep stage differently:
- REM sleep: the most temperature-sensitive stage. With excessive heat, REM time is significantly reduced, affecting memory consolidation and emotional processing.
- Deep sleep (N3): also affected by heat, though to a lesser degree. High temperatures can fragment this crucial stage for physical recovery.
- Light sleep (N1, N2): the most tolerant stage to temperature variations, though excessive heat still increases the frequency of micro-awakenings.
Practical tips for temperature control
If it's hot
- Ventilate the room in the evening when the outside cools down
- Use cotton or linen sheets instead of synthetic fabrics
- Place a fan aimed at an open window (it pushes hot air out)
- Take a lukewarm shower before bed: the subsequent drop in body temperature induces sleep
- Keep blinds closed during the day to prevent solar heat from entering
If it's cold
- Use layers of bedding instead of one very thick blanket (easier to adjust)
- Wearing socks to bed can help: cold feet send alert signals to the brain
- Warm the room before going to bed and lower the heating once you are asleep
For all seasons
- Maintain a constant temperature: sudden changes during the night interrupt cycles
- If you share a bed with someone who has different preferences, consider individual blankets
- Intense exercise raises body temperature for hours; avoid it 3–4 hours before bed
Body temperature vs. room temperature
It is important to distinguish between your body temperature and that of the environment. You can be in a room at 18°C and still feel warm if you use too much bedding, or cold if circulation to your hands and feet is poor.
A science-backed trick: warming your hands and feet before bed (with warm water or socks) dilates peripheral blood vessels, facilitating heat redistribution from the body's core to the exterior and speeding up the drop in core temperature needed to initiate sleep.