Periocular skin warming promotes body heat loss and sleep onset: a randomized placebo-controlled study.

Periocular skin warming was reported to have favorable effects on subjective and objective sleep quality. We hypothesized that enhancing body heat loss by periocular skin warming would reduce sleep onset and improve sleep quality. Eighteen healthy volunteers were asked to maintain wakefulness with their eyes closed for 60 min after applying either a warming or sham eye mask, followed by a 60-min sleep period. Compared to the sham, periocular warming increased the distal skin temperature and distal-proximal skin temperature gradient only during the 30-min thermal manipulation period. In the subsequent sleep period, periocular warming facilitated sleep onset, increased stage 2 sleep and electroencephalographic delta activity during the first half of the sleep period relative to the sham. These results suggest that periocular skin warming may accelerate and deepen sleep by enhancing physiological heat loss via the distal skin, mimicking physiological conditions preceding habitual sleep.