Why do we sweat when we are stressed?

While perspiration is most often seen as a biological thermostat designed to cool the body, sweat triggered by psychological pressure follows a completely different logic. It all begins in the heart of our brain, more precisely in the amygdala, the centre that manages emotions. When faced with a perceived threat, whether it is a physical danger or a stressful social situation such as speaking in public, the amygdala sends an alarm signal to the body. This message activates the sympathetic branch of the autonomic nervous system, triggering what biologists call the fight-or-flight response ("fight or flight" in English). A surge of catecholamines, such as adrenaline and noradrenaline, is then released into the body.

Nerve activation targets specific sweat glands in the epidermis.

In contrast to thermal sweat, which primarily engages the eccrine glands to expel water and salts, stress-induced sweat involves the apocrine glands instead, located mainly in the underarm area, the genital regions, on the palms of the hands and on the soles of the feet. These glands secrete a thicker fluid, rich in lipids and proteins. It is this particular chemical composition which, when it comes into contact with the resident bacteria on the skin, generates a stronger, more acidic odour, often associated with moments of anxiety.

Did you know? The moisture of the palms of the hands and the soles of the feet, produced by perspiration, increases the adherence and friction of the skin, providing a better grip for climbing and escaping. This stress-induced sweating stems from an ancestral survival mechanism that optimises the chances of responding effectively to the unexpected.

It should be noted that this sweat production is not linear. Research conducted in 1998 made it possible to visualise precisely the behaviour of the sweat glands in response to a direct emotional stimulus. By observing the skin under a microscope after producing a sudden, intense noise behind the heads of 11 volunteers, the researchers highlighted that secretion does not occur in a uniform manner: the glands respond according to a damped periodic oscillation. In practical terms, sweat is not expelled in a single flow, but in a series of four rhythmic peaks. The first interval between two sweat peaks lasts about 1.7 seconds, while the subsequent intervals systematically double in duration (3.2 and then 6.6 seconds). This mathematical pattern suggests that the body manages the absorption of an emotional shock like a physical shock wave that gradually diminishes.

Finally, this stress-induced sweat fulfils an invisible communication function inherited from our past. The compounds released by the apocrine glands act as chemical signals that are, in theory, capable of influencing those around us. Research suggests that we unconsciously detect the odour of another person’s “fear sweat”, which instantly heightens our own vigilance and sharpens our perception of negative facial expressions. This olfactory trail transmits an individual’s danger signal to others, enabling them to face it together.

It is important to recognise that stress-related sweating is one of the most difficult mechanisms to control, precisely because it escapes our conscious will. Unlike heat, which we can counteract by adapting the way we dress or behave, emotional sweat arises from an internal chemical reaction over which we have no control. For many people, the mere fear of sweating itself becomes a source of anxiety, creating favourable conditions for perspiration to occur.

To calm this nervous reactivity and prevent stress-induced sweating, you can try using breathing techniques before a stressful situation. To do this, breathe in deeply and slowly, hold your breath for two to three seconds, then exhale gently. Repeat several times, until you feel your heart rate settling down.

Tip : In anticipation of a stressful event, such as speaking in public, you can wear clothing made from natural, breathable fabrics, such as linen or cotton, to better manage sweating and prevent it from becoming visible, thereby avoiding fuelling the vicious circle of social embarrassment.

• OHHASHI T. & al. Physical stimuli and emotional stress-induced sweat secretions in the human palm and forehead. Analytica Chimica Acta (1998).

• ZIEGLER M. G. Psychological stress and the autonomic nervous system. Primer on the Autonomic Nervous System (2004).

• HARKER M. Psychological sweating: A systematic review focused on aetiology and cutaneous response. Skin Pharmacology and Physiology (2013).

• MEYER J. & al. Real sweating in a virtual stress environment: Investigation of the stress reactivity in people with primary focal hyperhidrosis. PLOS One (2022).

• NAUMANN N. & al. Hyperhidrosis: A central nervous dysfunction of sweat secretion. Dermatology and Therapy (2023).