Why do some people sweat so much?

Sweating is natural, yet it makes many people uncomfortable. Feeling sweat run down your back is hardly pleasant. And depending on what you are wearing, the thought that other people can see it can be embarrassing. But here is the reassuring part: if you do not sweat during exercise or when temperatures rise well above normal, that is when there may be a problem. “It’s true that, socially, we don’t like it, explains sports physician Mathieu Saubade. But physiologically, sweating is a good thing. People with certain conditions, or those at the extreme end of the spectrum who sweat very little, struggle significantly and overheat quickly. It can be seriously debilitating.” When the body produces very little sweat, it cannot release enough heat and therefore cannot regulate its temperature properly. In athletes, impaired sweating can lead to poor tolerance of prolonged exercise, as well as faintness, syncope, heatstroke and even heart attacks.

How does the body regulate its temperature?

Sweating and the evaporation of sweat form the body’s main thermoregulatory system. They allow the body to release some of its heat and maintain its temperature. Sweat glands, located beneath the skin, are responsible for producing sweat and come in two types: apocrine and eccrine glands. Apocrine glands are found in specific areas rich in hair, such as the armpits and scalp. Eccrine glands are distributed across almost the entire surface of the body, from the palms of the hands to the soles of the feet, including the face and forehead.

Eccrine glands are located deep in the dermis, one of the layers of the skin, where their secretory portion forms a narrow tube coiled in on itself. Sweat then reaches the skin’s surface through an excretory duct. “These are the glands that produce what you might call the useful kind of sweat, the sweat involved in thermoregulation , adds the physical and rehabilitation medicine specialist. Sweat is 99% water, with the remainder made up mainly of mineral salts and other substances.

Why some people sweat more than others

You often see it on public transport or during a training session. People are in similar surroundings or appear to be exercising at roughly the same intensity, yet some are far more soaked than others. The amount of sweat produced depends on several factors. Some are specific to the individual, including physiological characteristics, health, fitness level, age and sex.

Others are linked to conditions outside the body, particularly the type of exercise and the environment. “Sweat rate, meaning the amount of sweat produced per minute or per hour, is often around one litre per hour,” the researcher explains in relation to physical exercise. But he stresses that it can vary enormously: “Some people have fairly low sweat rates, around 0.5 or 0.8 litres per hour depending on the type of exercise, while others can easily exceed 1.5 litres per hour, reaching 3 or even 5 litres.”

That estimate can still vary, because the environment plays a crucial role in how sweat evaporates. “What matters is not so much how much sweat you produce, but the release of heat through the evaporation of those tiny water molecules,” he explains. If sweat does not evaporate, it simply runs down the skin in abundance, which can become irritating. “It can sting your eyes and cause chafing, for example under the arms,” he adds. That is when being “soaking wet” takes on its full meaning.

In very humid conditions, evaporation is much less effective. The body therefore cools itself less efficiently, and exercise can become harder to tolerate. In this context, acclimation is an important factor, particularly for athletes. It is the body’s ability to adapt gradually to its environment. In general, it takes 7 to 14 days to acclimatise to a transition from temperate conditions to a hot, humid environment. “The body will produce more sweat, so sweat rate will increase, and it will retain more salt.” Sweat contains water and electrolytes, particularly chloride and sodium, the two components of salt. The more sweat you lose, the greater your mineral losses can be.

Sweating causes water loss that the body needs to replace, particularly during exercise or in hot conditions. To estimate sweat losses during a workout, you can weigh yourself before and after the session, taking into account how much you drank. This makes it possible to tailor hydration to your own needs.

Insufficient hydration can cause headaches, reduce concentration and lead to sleep problems. “You should aim to replace roughly 80% of your losses. You do not need to replace 100% of them. If I lose one litre per hour, I do not need to drink one litre. But I should drink at least 600 to 800 millilitres. That is the rough target. After exercise, however, the recommendation is to drink one and a half times the amount of sweat lost,” he says.

Hyperhidrosis: when sweating becomes excessive

Sometimes sweating is excessive. It interferes with everyday life and causes concern. This is known as hyperhidrosis, an excessive production of sweat that goes beyond what the body needs to regulate its temperature. In primary hyperhidrosis, it is linked to overactivity of the sympathetic nervous system, which helps control sweating. People affected may sweat more in response to a small change in temperature, but also as a reaction to emotions.

They may sweat more with a slight change in temperature, but also in response to emotion. “They sweat more than normal every day. It can be socially difficult because they may have to change their shirts several times a night, and there can be odours. Bacteria multiply much more readily on damp skin. Physiologically, though, it is not particularly serious, except when someone with hyperhidrosis takes part in an endurance event.”

But sweating does not necessarily make you smell bad. “The unpleasant smell is not caused by sweat production itself, but by sweat remaining on the skin, which has its own microbiome made up of many different bacteria and viruses.” In a damp environment, bacteria on the skin can contribute to different odours depending on each person’s skin flora.

During hard exercise, sweating should not be a problem. “On the contrary, the more you sweat, the better,” Mathieu Saubade points out. The body is extremely well adapted to functioning within limits, but problems can arise when things become excessive. So do not hesitate to seek medical advice if sweating becomes intrusive or starts to affect your life.