Very few mammals perspire so what are the advantages of sweating for humans? Sports Scientist Andy Blow looks at how sweating could be a result of evolution and explains why humans sweat... 

Contents:

The dangers of overheating

Humans are endotherms.

This is a scientific term for ‘warm blooded’ and means that we regulate our own core body temperature without relying on the external environment in the way
that cold blooded creatures like reptiles are forced to.

We have to keep our core temperature in the range of about 97°F (36.1°C) to 99°F (37.2°C), as the dangers of Hyper- and Hypo- thermia lurk nearby if we deviate too far above or below this range.

There’s not a lot of wiggle room when it comes to overheating.

A core temperature over 104°F (40°C) can be life-threatening, although interestingly, a sustained temperature a little way north of this has been recorded in some elite athletes running in the heat.

As the heat generated as a bi-product of our internal metabolic processes increases our body temperature, we use several mechanisms to dissipate any excess to the environment.

During exercise, metabolic heat production rises largely in step with the intensity of work being done, so excess heat can be a significant problem when going hard, especially in a hot environment. 

So overheating can be a seriously performance-limiting factor in many endurance sports, as Jonny Brownlee found out in Cozumel in 2016

Why do humans sweat? 

The evaporation of sweat is the body’s most effective method of offloading heat if you’re working hard, especially in hot, dry conditions.

What’s interesting is that using sweating as a primary method of heat loss
is relatively unique to humans. Very few mammals perspire at all - and those that do all sweat quite a lot less than us humans.

Per unit of body surface area, we sweat about 2x as much as camels and about 5x as much as horses, who are a couple of the next most proficient sweaters.

Many mammals primarily lose heat through panting. This has the advantage of conserving fluid (and salt), but is less effective than the evaporation of sweat when the external environment is very hot. 

It’s widely believed we developed our ability to sweat due to having evolved on the hot dry plains of the African Savanna. 

Humans don’t have a very impressive top speed when compared with animals like antelope and onyx so, to successfully hunt these prey animals down, our ancestors needed to find ways to catch them that did not involve simply outpacing them. Even Usain Bolt would be left standing by most of the four-legged prey we were hunting a few thousand years ago!

The ability to sweat was our secret weapon, as it gave us the option to keep moving at a steady, aerobic pace during the hottest part of the day without significantly overheating.

Human hunters could track and chase down prey over several hours, running it into heat exhaustion through several hours of ‘Persistence Hunting’. 

How sweating impacts athletic performance

We rarely need to hunt down antelope in the desert these days, but we’re still incredibly well adapted to performing endurance exercise in hot, dry climates because we can sweat a great deal and the evaporation of all of this sweat keeps our core body temperature within safe limits.

We do tend to find things harder in very hot and humid environments though
due to reduced rate at which sweat can evaporate into wetter air.

The downside to our ability to sweat a lot to keep cool is that we need to consume a relatively large amount of fluid (and in some cases salt) to help us offset our much larger fluid losses. 

Exactly what and how much humans should drink in order to replace those sweat losses and maximise exercise performance has received a lot of attention in the last 100 years or so.

Whilst we understand this much better than we used to, it’s still an area of sports science where there’s no single consensus. This is perhaps because it depends on a large number of factors and there’s no single, neat ‘one-size-fits-all’ answer. That's why we give athletes personalised hydration advice off the back of our Sweat Tests

We have explored different aspects of the question of what and how much to drink in other blogs though if you want to explore this in more detail.

Further reading