Head hair reduces sweat rate during exercise under the sun.

The purpose of this study was to evaluate the effects of human head hair on thermoregulation during exercise carried out under solar radiation. 10 healthy male subjects (mean±SD: 25.1±2.5 yr; height: 176.2±4.0 cm; weight: 73.7±6.7 kg; VO(2max) 56.2±5.3 mLO(2)·kg (-1)·min (-1)) took part in 2 1 h-long trials of continuous exercise on a treadmill at 50% VO2(max) under solar radiation that were separated by at least 2 days. Whereas for the first trial they retained their natural head hair (HAIR), in the second trial their hair was totally shaved (NOHAIR). Several properties were measured, including environmental heat stress (Wet Bulb Globe Temperature index - WBGT, °C), heart rate, rectal temperature, skin temperature, head temperature, and global sweat rate. The main findings were that whereas there was a lower sweat rate in the HAIR condition (HAIR: 7.08±0.79 vs. NOHAIR: 7.67±0.79 g·m (-2)·min (-1); p=0.03), there were no significant differences in any of the other variables between the HAIR and NOHAIR trials. In conclusion, the presence of head hair resulted in a lower sweat rate.