Thermal sensation and comfort in women exposed repeatedly to whole-body cryotherapy and winter swimming in ice-cold water.

Whole-body cryotherapy (WBC; -110 degrees C) and winter swimming (WS) in ice-cold water are severe ambient cold exposures, which are voluntarily practiced by humans in minimal clothing. The purpose was to examine thermal sensation and thermal comfort associated with WBC and WS. Twenty women similar in body mass index, age, physical activity, and use of hormonal contraception were pairwise randomized either to the WBC group or the WS group. The duration of each WBC exposure was 2 min, which was repeated three times per week for 3 months (13 weeks). Similar exposure frequency was used for the WS group, but each exposure lasted 20 s in outdoor conditions. Thermal sensation and comfort were asked with standard scales. After WBC, 65% of the thermal sensation votes were 'neutral' or 'slightly cool.' After WS, 81% of the thermal sensation votes were 'warm,' 'neutral,' or 'slightly cool.' Majority of comfort votes immediately after exposures in WBC group (98%) and in the WS group (93%) were 'comfortable' or 'slightly uncomfortable.' Thermal sensation and comfort became habituated in both groups at an early stage of trials, but the changes were less conclusive in WS group due to variable conditions outdoors. In the WBC group, cold sensation was less intense already after the second exposure. In conclusion, repeated exposures to WBC and WS in healthy women were mostly well tolerated and comfortable. The results indicate that during repeated severe whole-body cold stress of short duration, thermal sensation and comfort become habituated during the first exposures.