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 core of our brain, specifically in the amygdala, the center that processes emotions. When faced with a perceived threat, whether it is a physical danger or a stressful social situation such as public speaking, 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. A surge of catecholamines, such as adrenaline and noradrenaline, is then released throughout the body.

Nerve activation targets specific sweat glands in the epidermis.

Unlike thermal sweat, which primarily relies on the eccrine glands to eliminate water and salts, stress-induced sweat mainly activates the apocrine glands, located predominantly in the armpits, in the genital areas, 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 skin’s resident bacteria, produces a stronger, more acidic odor, often associated with moments of anxiety.

Did you know? The moisture on the palms of the hands and the soles of the feet produced by sweating increases the adhesion and friction of the skin, providing a better grip for climbing and escaping. This stress-induced sweat comes from an ancient survival mechanism that enhances our ability to respond to unexpected situations.

It is important to note that this sweat production is not linear. Research conducted in 1998 precisely visualized how sweat glands behave in response to a direct emotional stimulus. By observing the skin under a microscope after producing a sudden, loud noise behind the heads of 11 volunteers, the researchers showed that secretion does not occur uniformly: the glands respond according to a damped periodic oscillation. In practical terms, sweat is not expelled in a single continuous 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 processes the impact of an emotional shock in a manner similar to a physical shock wave that gradually diminishes.

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

It is important to recognize 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 respond to by adjusting the way we dress or behave, emotional sweating 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 favorable conditions for sweating to occur.

To calm this neural reactivity and prevent stress-related sweating, you can try using breathing techniques before a stressful situation. To do this, inhale deeply and slowly, hold your breath for two to three seconds, then exhale gently. Repeat several times, until you feel your heart rate begin to slow.

Advice : In anticipation of a stressful event, such as public speaking, you can wear clothing made from natural, breathable materials like linen or cotton to better manage sweating and prevent it from becoming visible, thereby avoiding reinforcement of the vicious cycle 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).