Why does our body sweat?

2 to 4 million

of sweat glands over the entire body.

≈ 1 liter

of sweat lost per day on average without physical activity.

4 minutes to understand your skin. Our dermatological diagnostic guides you toward the ideal skincare for your specific needs. Simple, quick, personalized.

1. Perspiration primarily serves to regulate body temperature.

The sweating process primarily plays a thermoregulatory role.

In other words, it enables the organism to maintain a relatively stable internal temperature, around 37°C, despite variations in the environment or increased heat production by the body itself. This is a key point, because the functioning of enzymes, cells, and organs depends on a precise thermal balance. If body temperature rises too high, this functioning can be disrupted.

One of the main internal factors that can cause an increase in temperature is physical activity. When a muscle contracts, not all of the chemical energy it uses is converted into useful movement. A significant portion is dissipated as heat. In practical terms, this means that during physical exertion, muscles generate a large amount of heat in addition to the mechanical work they perform. The more intense the exercise, the greater this heat production becomes. This excess heat then needs to be removed from the body.

This is where sweating comes into play. The eccrine sweat glands, distributed over almost the entire surface of the body, secrete sweat onto the skin. This sweat is composed mostly of water, with a small amount of mineral salts and other dissolved compounds. By itself, the presence of water on the skin is not enough to cool the body. The actual cooling mechanism comes from its evaporation. Indeed, when sweat evaporates, it absorbs thermal energy from the skin surface. In other words, to move from the liquid state to the gaseous state, water requires energy, which it partly draws from the body’s heat. This is how sweating enables efficient heat dissipation.

It is estimated that about 1 gram of evaporated sweat allows the body to release nearly 2.4 kJ of heat. The amount of sweat produced therefore depends closely on the amount of heat the body needs to eliminate.

What are the differences between eccrine and apocrine sweat glands?

There are two main types of sweat glands:

Eccrine glands: Very numerous and distributed over almost the entire surface of the body, they are active from birth and secrete a watery sweat that is low in lipids, primarily in response to an increase in body temperature.
Apocrine glands: Located only in certain areas (armpits, genital region), they become active at puberty and produce a thicker secretion that is rich in organic compounds, particularly in response to emotions or stress.

Note that if the air is dry and circulates well, sweat evaporates easily and cools the body efficiently. Conversely, when the air is humid, evaporation becomes more difficult. Sweat can then run off without really fulfilling its cooling function. This is why, at the same temperature, we sweat more when the air is humid. It is the nervous system that controls this process. The hypothalamus, a region of the brain involved in regulating body temperature, receives information from thermoreceptors located in the skin and within the body. When it detects a rise in temperature, it activates the eccrine glands via the autonomic nervous system, more specifically the cholinergic sympathetic fibers, which triggers sweating.

Note : It is worth noting that the amount of sweat produced is not fixed. It can adapt over time, particularly in the case of heat acclimation. After several days of repeated exposure to hot conditions, the body becomes more efficient: it begins to sweat earlier and often more, while losing proportionally less sodium in the sweat. This adaptation improves heat tolerance and reduces the risk of hyperthermia.

Thus, we sweat first and foremost because the body needs to protect its internal temperature.

2. We also sweat in response to emotions.

Sweating is not limited to a thermal response. It can also be triggered by emotions such as stress, anxiety, fear, or even excitement. Unlike heat-related sweating, which is mainly regulated by the hypothalamus in response to an increase in body temperature, emotional sweating is triggered by brain structures involved in emotion processing, such as the limbic system, particularly the amygdala. When the brain perceives a situation as stressful or threatening, it activates the sympathetic nervous system, which, among other effects, stimulates the sweat glands.

Emotional sweating is very rapid and can appear just a few seconds after an emotional stimulus.

This type of sweating affects specific areas of the body, particularly the palms of the hands, the soles of the feet, the armpits, and sometimes the forehead, where apocrine sweat glands are found. Of course, emotional sweating varies greatly from one individual to another. Some people have an increased sensitivity of the sympathetic nervous system, which can result in more pronounced emotional sweating, sometimes referred to as hyperhidrosis when it becomes excessive and affects quality of life.

3. Sweat contributes to maintaining the skin’s balance.

While sweating is primarily a thermoregulatory mechanism, it also plays a more subtle but real role in maintaining the physiological balance of the skin. The sweat produced by eccrine glands is not composed of water alone: it also contains a variety of molecules, such as sodium, potassium, lactate, urea, as well as certain amino acids, which contribute to maintaining skin hydration.

These compounds are, for some of them, part of what are called natural moisturizing factors (NMF), whose role is to retain water in the stratum corneum, the outermost layer of the epidermis.

Beyond hydration, sweat also appears to contribute to the skin’s defense against external aggressions. Sweat glands are able to produce and secrete antimicrobial peptides, such as dermcidin, cathelicidin, and lactoferrin. These molecules help to limit the proliferation of certain microorganisms on the surface of the skin, thereby contributing to the maintenance of the skin microbiome. Perspiration may therefore play a role, to some extent, in protecting against certain skin infections, although this function is still being investigated.

Sweat also plays a role in maintaining the acidity of the skin’s surface. In fact, some of its components, such as lactate, help to maintain a pH that is slightly acidic, around 4.5–5.5, which is favorable to the balance of the microbiome and to the integrity of the skin barrier. This acidity notably limits the growth of pathogenic bacteria and supports the activity of enzymes involved in renewing the stratum corneum.

Note : While moderate sweating can help support skin hydration and protection, excessive or prolonged sweating, or sweating associated with occlusion, such as when wearing tight clothing, can instead weaken the skin barrier and promote irritation. The impact of sweat on the skin therefore depends on the context and its intensity.

4. Can sweating “detoxify” the body?

The idea that sweating helps eliminate toxins from the body is widely held. Saunas and intense exercise are indeed often presented as ways to speed up this elimination. However, from a physiological perspective, this view is very simplified. It is true that sweat contains traces of exogenous compounds, such as metals, pollutants, or even alcohol. However, their presence in sweat does not mean that sweating is a major elimination pathway. Sweat is produced from interstitial fluid, which itself is derived from blood plasma, and its composition partly reflects that of this compartment. It is therefore more of a passive diffusion phenomenon than an active detoxification process.

The true organs involved in eliminating unwanted substances are the liver and the kidneys. The liver converts toxins into metabolites that are easier to eliminate, while the kidneys filter the blood to excrete these substances in the urine. For example, about 90% of ingested alcohol is metabolized by the liver, with the remainder being eliminated in small amounts through exhaled air, urine, and sweat. The contribution of sweating to this elimination is therefore marginal.

Just as sweating does not make it possible to eliminate fat mass, excessive sweating, for example after a sauna session, is not necessarily accompanied by an increased elimination of undesirable substances.

5. Certain diseases or medications can alter sweating.

The proper functioning of sweating is sometimes altered. These changes can manifest as excessive sweating (hyperhidrosis) or, conversely, insufficient sweating (hypohidrosis or anhidrosis). Certain diseases directly affect the functioning of the sweat glands or the nerve pathways that control them. For example, diabetes or multiple sclerosis can disrupt the regulation of sweating. In other cases, such as congenital anhidrosis, the sweat glands are absent or poorly functional, which impairs the body’s ability to dissipate heat and can lead to heat intolerance.

Conversely, an overactivity of the sympathetic nervous system following hormonal changes, such as hyperthyroidism or simply menopause, can lead to excessive sweating. Certain medications can also stimulate sweat production, such as antidepressants and analgesics.

These alterations are not insignificant.

Insufficient sweating can limit the body’s ability to cool itself, increasing the risk of heat stroke. Conversely, excessive sweating can affect quality of life, particularly on social and emotional levels. This is why, if you notice any change in your sweating, you should not hesitate to talk to a healthcare professional to identify the cause and to receive appropriate recommendations.