Sleep · Environment

Sleep temperature: why sleeping cool is better

3 Min. read YUTHI Redaktion

Your body needs to lower its core temperature in order to fall asleep. This makes room temperature one of the most powerful yet most underestimated levers for good sleep – with a clear recommendation from research.

Temperature and Sleep: A Biological Mechanism

Falling asleep is not a passive process. Your body actively lowers its core temperature — by about 1 to 2 degrees Celsius — as part of the process of falling asleep. This drop in temperature is a central signal to the brain: now it is time to sleep. Harding, Franks and Wisden (Front Neurosci, 2019) described in a comprehensive review how closely sleep and thermoregulation are linked — sleep systems and heat-control centres in the hypothalamus overlap anatomically and functionally.

The heat has to leave the body — through the skin, especially at the hands and feet. There you find arteriovenous anastomoses, specialised vascular connections that channel large volumes of blood to the surface and can release heat. Warm hands and feet therefore mean: the body is actively cooling its core temperature.

The Optimal Bedroom Temperature

Most sleep research institutions recommend a room temperature between 15 and 19 degrees Celsius. Van Someren and colleagues (Prog Brain Res, 2006) showed that skin temperature and sleep quality correlate closely — a slightly elevated skin temperature (from a warm, not hot environment) promotes sleep onset, while overheating disrupts it.

What is optimal varies individually: women tend to prefer slightly higher sleep temperatures than men, and thermoregulation changes with age. As a starting point, 18 degrees is a good reference value — noticeably cooler than most living rooms, but warm enough not to feel cold.

The Warm Bath Trick: Cooling Through Warmth

A warm bath or warm shower (around 40 to 42 degrees) one to two hours before falling asleep can paradoxically speed up the process of falling asleep. Raymann, Swaab and Van Someren (Brain, 2008) documented how targeted skin warming reduces sleep-onset latency. The mechanism: the warm water dilates the blood vessels in the skin, blood flows to the surface, and the body releases heat more quickly — the core temperature drops more efficiently.

The opposite — exercising shortly before bed, taking a hot shower, or lying in an overheated flat — delays this cooling process and extends the time it takes to fall asleep. Not because you would be too stimulated, but because the thermal mechanism is blocked.

Practical Steps for the Right Sleep Temperature

Actively cool the bedroom: in summer, keep blinds or shutters closed during the day and air the room in the evening before you sleep. In winter, the bedroom does not need to be as warm as the rest of the flat — 17 to 18 degrees is a good target. If you sleep with a partner who has a noticeably different temperature preference, separate duvets with different warmth levels can be a simple solution.

Wool and breathable materials are superior to synthetic fillings because they absorb and release moisture more effectively. People who sweat heavily benefit from cooling mattress toppers or well-ventilating slatted frames. The body regulates a great deal on its own — as long as the ambient temperature does not hinder the process.

How the YUTHI App Helps You

Log it in the YUTHI app when you have changed something about your bedroom temperature — for example by airing the room more consistently or lowering the temperature. Comparing this with your sleep quality scores from previous weeks, you can quickly see whether the change made a difference. Combine this with entries about warm baths or sporty evenings to get the full picture of your thermoregulation.

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