Use body temperature to assist sleep onset

Drop your core temperature before bed — the temperature fall is a key Process C signal for sleep onset.

Why it works

Core body temperature follows the circadian rhythm and must fall for sleep to initiate and maintain. The mechanism is directly tied to Process C: the clock drives both the melatonin rise and the temperature drop as part of the same nighttime biological signature. Helping this drop along — through a warm bath or shower, or by keeping the bedroom cool — accelerates sleep onset and maintains sleep architecture through the night.

How to do it

1. Keep the bedroom temperature between 65–68°F (18–20°C) if possible — cooler than the rest of the house.
2. A warm bath or shower thirty to ninety minutes before bed paradoxically accelerates the temperature drop: blood moves to the skin surface, dissipating heat.
3. Avoid vigorous exercise within two hours of bedtime if it significantly raises your core temperature.

Evidence

Core body temperature decline as a correlate of sleep onset is well established; warm bathing accelerating the subsequent temperature drop and improving sleep onset has been supported in controlled studies. (rct)

Optimal temperature varies between individuals, particularly by age and sex; the direction of the effect (cooler is better for sleep) is reliable, the exact target temperature is not universal.

Sources

• Haghayegh et al. (2019), before-bedtime passive body heating for sleep, Sleep Medicine Reviews meta-analysis

Common mistake

A hot shower right before getting into bed, which raises rather than lowers core temperature at the bedtime moment, delaying sleep onset despite the eventual drop.