Can a bed that is too warm cause me to sleep worse?

A bed that is too warm disrupts your sleep because your skin gets too hot, you start to sweat, and your body temperature does not drop enough. That last point is crucial: your body needs to lower its core temperature slightly in order to fall asleep and stay asleep. An overly hot sleep environment blocks that process.

That does not mean cold is automatically better. People who always feel cold in the bedroom at night also sleep worse. Japanese research showed that people who felt cold achieved significantly lower sleep-quality scores on average. There is therefore a comfort zone, and both too warm and too cold fall outside it.

What does help is having warm feet in an otherwise cool bedroom. Wearing bed socks at a room temperature of 23 degrees showed, in a small laboratory study, that people fell asleep faster, slept longer, and woke up less often. The idea is that warmer feet cause the blood vessels near the skin to open up, allowing heat to flow out of the body more effectively so that core temperature drops slightly. Note: this was a study with only six young men, so do not draw sweeping conclusions from it.

Active cooling via a specially designed mattress, in which heat was removed through the skin, also showed promising effects on sleep-onset time and sleep experience in a small exploratory study. However, that study also included only eleven participants, all young men. Both findings are interesting but have not yet been confirmed on a broader scale.

In practical terms: make sure your sleep environment does not feel too warm, choose breathable bedding, and avoid clothing or blankets that encourage sweating. If your feet tend to get cold quickly, socks can actually help you. The ideal bed temperature for most people falls somewhere in the cool-but-not-cold range, although this varies from person to person.