You've heard the one about how men sweat, women glow? Well, there may be a drop of truth to it, so to speak. A new study out of Japan finds that men are efficient sweaters, as opposed to women, who have to do much more to break a sweat. But, how come?
The study was conducted by scientists at Osaka International University and Kobe University in Japan, and published in the journal Experimental Physiology. It looked at four groups of cyclists—trained vs. untrained, women vs. men—and had them cycle for an hour with increasing intervals of intensity. Overall, the trained group sweated more than the untrained group: "The mean local sweating rate (SR) on the forehead, chest, back, forearm and thigh was significantly greater in the trained subjects than in the untrained subjects of both sexes," the study says. But the trained men sweated much more than the trained women, and the least sweaty group of all was the untrained women. In short, women who don't train need to raise their body temperature much higher before they can start sweating.
Sweating, of course, is adaptive—it is a cooling system for the body, and thus will allow an athlete to continue exercising once he begins to get hot. Women, therefore, "are at a disadvantage when they need to sweat a lot during exercise, especially in hot conditions," said study coordinator Yoshimitsu Inoue. In general, physical fitness will lower the core temperature needed to activate the sweat response, but in this study, it will do so less for women than for men.
A possible explanation is testosterone, the presence of which, previous research indicates, triggers sweating sooner. As the authors write, "In the present study, we did not measure testosterone levels, hence the effects of testosterone on the sex difference in the effects of training are unclear. However, based on our findings and previous reports, it is conceivable that testosterone levels affect the sweat gland response. Further studies are necessary to clarify this point."
Or, the explanation may be evolutionary. "Women generally have less body fluid than men and may become dehydrated more easily," Inoue says. "Therefore, the lower sweat loss in women may be an adaptation strategy that attaches importance to survival in a hot environment, while the higher sweat rate in men may be a strategy for greater efficiency of action or labour." But whatever the reason, this is a good opportunity to remember that sweat isn't gross—it's great.