Infants sleeping outdoors in a northern winter climate: skin temperature and duration of sleep

Aim: The aim of the study is to describe the relationships among thermal environment, skin temperatures and infants’ daytime outdoor sleep duration in northern winter conditions. Methods: This study is a cross‐over observational study. Skin temperatures of three‐month‐old infants were recorded from seven skin sites continuously throughout outdoor (n = 34) and indoor sleep (n = 33) in the families’ homes. The duration of the sleep was observed, and temperature and the air velocity of the environment were recorded. Results: Skin temperatures increased towards the end of indoor sleeping, whereas they decreased during outdoor sleeping. The cooling rate of mean skin temperature (T_sk) increased in lower outdoor temperatures (r_s = 0.628, p < 0.001) in spite of increased clothing. On some occasions, cold extremities were observed, suggesting slight deviations from thermoneutrality. Sleep time was 92 min longer in outdoors than in indoors. However, outdoor sleep duration was shortened when the cooling rate of T_sk increased (r_s = 0.611, p < 0.001). Conclusion: The longest sleep was recorded outdoors when the cooling rate of T_sk was minimal. Restriction of movements by clothing probably increases the length of sleep, and a cold environment makes swaddling possible without overheating. A decrease in ambient temperature increased the cooling rate, suggesting that the cold protection of the clothing compensated only partly for the increased heat loss.