March 6, 2017

The science of sweat

The amount people sweat is due to size rather than gender

Conventional wisdom has it that men sweat more than women, or as the Victorian-era saying puts it, “horses sweat, gentlemen perspire, but ladies merely glow”. And scientific research appeared to support that view. However, a study by researchers from the University of Wollongong (UOW) and Japan’s Mie Prefectural College of Nursing has shown that women are just as sweaty as men.

The research paper, published in Experimental Physiology, shows that differences in the amount that people sweat are due to body size rather than gender. Big people sweat more than small people.

Study co-author Associate Professor Nigel A.S. Taylor from UOW’s School of Medicine said the body has two main ways to cool down: sweating is one, the other is to increase blood flow to the skin's surface. The study found that smaller males and females relied more on increased circulation to cool down, while larger males and females relied more on sweating.

“We know that all objects lose heat through their surfaces,” Professor Taylor said. “If you compare a metallic plate and a sphere, both with the same mass and both heated to the same temperature, the plate will cool much faster when placed in cool air because it has a larger surface area.”

The same principle applies to people: smaller people have more surface area per kilogram of body mass than larger people and so are able to cool themselves more efficiently by increasing blood flow – bringing heat – to the surface of their skin. Larger people have to sweat more to get the same cooling effect.

“We looked at 60 people – 36 men and 24 women – with a very wide range of sizes, all university students, all at equivalent health, fitness and adiposity [body fat] levels,” Professor Taylor said. “We then brought every one of them to the same deep-body temperature (exercising in warm conditions), and when they each obtained a steady state temperature, we measured their skin blood flow and sweating responses”

“What we found was that all of the participants who were on the small side, whether they were men or women, preferentially lost heat by increasing their skin blood flow, and all of those who were on the larger side preferentially lost heat through sweating.

“We found that less than 5 per cent of the difference in the heat loss between men and women could be explained by their gender – so almost nothing. It was all about body size and shape, which makes perfect sense because we evolved to be really efficient and why would someone start to sweat if they could rely on another, more efficient mechanism to cool down?”

On average women are smaller than men, so an average-sized woman is likely to sweat less than an average-sized man, but that is due to her size rather than her gender.

Professor Taylor said the reason this study showed a different result to previous research was due to the use of a different experimental design; one that was best suited to answering the question of interest.

“Many studies actually perpetuated the myth that men sweat more than women because they either didn't match their subjects for fitness and exercise behaviours, they didn't get them to exercise at the same intensity relative to their body size or they didn’t produce the same elevation in deep-body temperature across all participants,” Professor Taylor said.

“It’s all about experimental control. To answer questions such as these, we must ensure that the only thing that is different between our participants, and the stresses to which we expose them, is their gender. Because we had all these variables matched, our participants all worked at the same relative workload and so they all reached the same deep-body temperature.

“Under these conditions, we were able to observe these unique results.”