Ice slurry ingestion reduces both core and facial skin temperatures in a warm environment

Internal body cooling by ingesting ice slurry has recently attracted attention. Because ice slurries are ingested through the mouth, it is possible that this results in conductive cooling of the facial skin and brain. However, no studies have investigated this possibility. Thus, the aim of this study was to investigate the effects of ice slurry ingestion on forehead skin temperature at the point of conductive cooling between the forehead skin and brain. Eight male subjects ingested either 7.5g/kg of ice slurry (-1°C; ICE), a cold sports drink (4°C; COOL), or a warm sports drink (37°C; CON) for 15min in a warm environment (30°C, 80% relative humidity). Then, they remained at rest for 1h. As physiological indices, rectal temperature (Tre), mean skin temperature, forehead skin temperature (Thead), heart rate, nude body mass, and urine specific gravity were measured. Subjective thermal sensation (TS) was measured at 5-min intervals throughout the experiment. With ICE, Tre and Thead were significantly reduced compared with CON and COOL conditions (p<0.05). The results of the other physiological indices were not significantly different. TS with ICE was significantly lower than that with CON and COOL (p<0.05) and was correlated with Tre or Thead (p<0.05). These results indicate that ice slurry ingestion may induce conductive cooling between forehead skin and brain, and reduction in core and forehead skin temperature reduced thermal sensation.