Sweating : an essential physiological process
Sweating is a natural, vital process regulated by the autonomic nervous system. Its main role is to keep body temperature stable (around 37 °C), through the evaporation of sweat produced by the sweat glands. These glands, distributed throughout the skin, are of two types :
- Eccrine glands, the most numerous, produce watery, odourless sweat for temperature regulation.
- Apocrine glands, located mainly in the underarms, groin and breast areolae, secrete thicker sweat that can cause body odour when broken down by bacteria.
Under normal circumstances, the amount of sweat produced is proportional to the body's thermal requirements, particularly during physical activity, emotional stress or in response to a high ambient temperature. In excessive sweating, however, this regulation is disrupted.
Primary hyperhidrosis
The most common form of excessive sweating is primary or essential hyperhidrosis. It accounts for around 90 % of cases and often begins in adolescence or early adulthood, with no identifiable underlying condition.
In primary hyperhidrosis, the mechanism involved is overactivity of the sympathetic cholinergic fibres supplying the eccrine sweat glands. This overstimulation is usually localised : this is known as focal hyperhidrosis. The most frequently affected areas are the palms (palmar hyperhidrosis), soles (plantar hyperhidrosis), underarms (axillary hyperhidrosis), face and scalp (craniofacial hyperhidrosis).
This form of excessive sweating is generally bilateral and symmetrical, worsens with stress or emotion and tends to decrease during sleep.
Studies have shown that nearly 30 to 50 % of people with primary hyperhidrosis have a family history. There therefore appears to be a genetic predisposition, although the gene or genes involved have not yet been formally identified.
Secondary hyperhidrosis
Unlike primary hyperhidrosis, secondary hyperhidrosis results from an identifiable medical condition, medicine or hormonal cause. It often presents as generalised sweating and can occur at any age, even in people with no previous history.
Endocrine conditions
Hormonal imbalances are among the most common causes :
- Hyperthyroidism : excess thyroid hormone production speeds up the basal metabolic rate, increasing heat production and therefore sweating.
- Menopause : hot flushes accompanied by heavy sweating are linked to fluctuating oestrogen levels.
- Hypoglycaemia : often associated with feeling unwell, it can cause profuse sweating.
- Phaeochromocytoma : this rare adrenal gland tumour causes episodes of high blood pressure with cold sweats.
Infectious, neurological and oncological causes
Some infectious conditions, particularly chronic febrile illnesses such as tuberculosis or HIV, may be accompanied by night sweats.
Neurological diseases such as Parkinson's disease, diabetic autonomic neuropathy or certain spinal cord injuries disrupt sweat regulation.
Finally, in some cases, excessive sweating may be a paraneoplastic symptom preceding the discovery of cancer, particularly lymphoma (unexplained profuse night sweats).
Medicines and substances
Many medicines can cause secondary excessive sweating. Those most frequently implicated include :
- Antidepressants (particularly serotonin reuptake inhibitors).
- Certain diabetes medicines (such as insulin).
- Anticholinesterase medicines.
- Opioid painkillers.
- Hormone replacement treatments.
The use of psychoactive substances (alcohol, caffeine, stimulant drugs such as cocaine or amphetamines) can also trigger excessive sweating.
Emotional factors : stress
It should be emphasised that stress and anxiety, without being the primary cause, aggravate excessive sweating, particularly its primary form. Eccrine sweat glands are sensitive to the adrenaline released during psychological tension. This link explains why symptoms increase in emotional situations : job interviews, social interactions or public speaking.
This psychophysiological vicious circle can lead to anticipatory anxiety, further increasing sweat production, which often warrants a comprehensive treatment approach including psychological or behavioural support.
Which factors can worsen hyperhidrosis ?
Several factors can intensify the symptoms of hyperhidrosis, particularly its primary form.
The intensity of excessive sweating is not constant : it can vary from day to day, between seasons or according to hormonal circumstances, sometimes making the condition difficult to assess. Many patients report more pronounced sweating episodes in summer, during heatwaves or in enclosed spaces. Beyond the outside temperature, however, other factors can worsen symptoms.
Physiologically, periods such as puberty, the menstrual cycle and menopause are often associated with worsening symptoms. This is explained by hormonal modulation of the autonomic nervous system, which partly controls sweat gland activity. In some women, unusual sweating before or during menstruation is a recurrent symptom. Similarly, hot flushes associated with perimenopause may be accompanied by excessive sweating, sometimes mistaken for true hyperhidrosis.
Chronic stress, performance anxiety and states of psychological hypervigilance also play a role in worsening symptoms. The more a patient fears sweating, the more it tends to occur — creating a particularly powerful vicious circle. This link between the central nervous system and the sweating system is particularly marked in palmar or facial hyperhidrosis.
Finally, external factors such as wearing synthetic clothing, drinking coffee or alcohol, or wearing enclosed shoes for prolonged periods can create skin conditions conducive to heavier sweating or poor moisture evaporation. Although these factors do not cause the condition, they contribute to its visibility and the discomfort it produces.
Recognising these aggravating factors enables patients to adopt — alongside medical treatment — a suitable lifestyle that respects their skin and physiology.
Why do we sweat more as we age ?
With age, the body undergoes physiological and hormonal changes that may disrupt temperature regulation. In women, menopause is frequently accompanied by hot flushes and night sweats due to the sharp fall in oestrogen levels. In men too, andropause can cause hormonal fluctuations leading to excessive sweating. In addition, the greater prevalence of certain chronic conditions in older people (diabetes, thyroid disorders, cardiovascular conditions), together with increased medicine use, also contributes to this tendency to sweat more.
Which hormone causes sweating ?
Sweat secretion is primarily stimulated by acetylcholine, a neurotransmitter of the autonomic nervous system that activates the eccrine sweat glands. However, certain hormones play a significant indirect role. Thyroid hormones increase the basal metabolic rate, boosting body heat production and therefore sweating. Adrenaline and noradrenaline, released in response to stress, also intensify sweating, particularly in areas rich in eccrine glands such as the palms and underarms. Finally, falling oestrogen levels in menopausal women destabilise the hypothalamic thermostat, causing heavy sweating.
Which diseases cause excessive sweating ?
Several medical conditions can cause excessive sweating. Hyperthyroidism, through increased energy expenditure, is a common cause. Chronic infectious conditions such as tuberculosis or HIV can cause heavy night sweats. Lymphomas, particularly Hodgkin's disease, are known to cause unexplained excessive sweating. Diabetes, particularly with autonomic neuropathy, and adrenal tumours such as phaeochromocytoma should also be considered. Identifying the underlying cause is essential to guide treatment.
Which deficiency causes sweating ?
Certain nutritional deficiencies, although rarely the primary cause of hyperhidrosis, can worsen existing symptoms. Magnesium deficiency, for example, can disrupt autonomic nervous regulation and intensify stress responses, thereby promoting increased sweating. Similarly, vitamin D deficiency is sometimes associated with excessive scalp sweating in infants, although this association is less clearly demonstrated in adults. Excessive sweating should not, however, be attributed to a deficiency without prior medical assessment.
Does drinking more mean sweating more ?
Drinking water does not directly increase sweating, but it plays an essential role in maintaining thermal homeostasis. Conversely, excessive and unnecessary hydration may, in some cases, place additional demands on the mechanisms that eliminate water, including through sweat, particularly in hot weather or during physical activity. However, this phenomenon remains marginal : the body sweats to regulate its temperature, not to eliminate excess water consumed.
Can stress and anxiety cause excessive sweating?
Stress and anxiety are major factors in amplifying hyperhidrosis, particularly its primary form. Stimulation of the sympathetic nervous system during emotional tension releases adrenaline, causing intense activation of the eccrine glands. This often leads to localised sweating of the hands, feet or face. This phenomenon, called emotional sweating, can be disabling in social or professional settings, highlighting the value of an integrated treatment approach, sometimes incorporating mind-body techniques.
Can excessive sweating be a side effect of certain medicines ?
Yes, many medicines can cause excessive sweating as a side effect. Among the best known are antidepressants (particularly serotonin reuptake inhibitors), antipyretics, antihypertensives such as propranolol and glucose-lowering medicines such as insulin. Certain hormonal treatments, opiates and anticholinesterase medicines may also be involved. If hyperhidrosis has developed recently, it is essential to review all current treatments with the prescribing doctor.
Is hyperhidrosis more common in summer ?
Primary hyperhidrosis, although present throughout the year, tends to worsen in summer due to higher temperatures and ambient humidity. Temperature regulation is under greater demand, increasing sweat secretion. In addition, emotional sweating is exacerbated by thermal discomfort, particularly in poorly air-conditioned public or professional environments. However, secondary hyperhidrosis is not always seasonal and depends mainly on the underlying cause.
Which foods increase sweating ?
Certain foods, described as thermogenic, can intensify sweating by stimulating metabolism or causing a vascular response. These include spicy foods (chillies, curry, ginger), which activate the TRPV1 receptors involved in the sensation of heat. Caffeine and alcohol are also known to increase sweating because of their vasodilating effect and stimulating action on the central nervous system. Patients with hyperhidrosis may therefore benefit from adjusting their diet to limit these triggers.
