Sweat, And Why It Varies So Much Between People

Sweating heavily is widely read as being unfit or overweight. The physiology points the other way: an efficient cooling system starts earlier and produces more.

Evaporation is the only cooling route that works in heat

The body loses heat by radiation, conduction and convection, but all of these require the surroundings to be cooler than the skin. Above that point they stop working.

Evaporation continues regardless, because it removes heat by converting liquid water to vapour, which consumes a large amount of energy per unit of water.

This is why sweat that drips is wasted. Only the portion that evaporates from the skin removes heat, and humidity is what determines how much of it can.

Two kinds of gland, doing different jobs

Eccrine glands are distributed over almost the whole body and produce the watery, largely odourless sweat responsible for temperature regulation.

Apocrine glands are concentrated in the armpits and groin, become active at puberty, and secrete a richer fluid into hair follicles that skin bacteria then break down.

Body odour therefore comes from bacterial action rather than from sweat itself, which is why antiperspirants and deodorants work by different means and are not the same product.

Fitness and acclimatisation increase output

Repeated heat exposure produces adaptation over one to two weeks. Sweating begins at a lower core temperature, more glands are recruited, and total output rises.

Acclimatised sweat also contains less sodium, because the glands reabsorb more of it, which conserves salt during prolonged heat exposure.

Trained people show the same pattern. Their systems begin cooling sooner, so at the same workload they sweat more, which is the opposite of the popular interpretation.

Not all sweating is about temperature

Emotional sweating is a separate response, driven by the stress system and concentrated on the palms, soles, forehead and armpits rather than distributed for cooling.

Palmar sweating in particular is thought to improve grip, which fits its appearance under threat and its indifference to ambient temperature.

Spicy food produces yet another route, triggering heat receptors that report a temperature that is not actually present, and the cooling response follows the false report.

What amount is worth investigating

Sweating heavy enough to interfere with work, damage documents or require multiple changes of clothing is a recognised condition rather than an extreme of normal, and it has treatments.

Sweating that is new, occurs mainly at night, is drenching, or comes with weight loss or fever is a different situation and needs medical assessment.

Sudden sweating with chest pain, breathlessness or nausea should be treated as an emergency, since it is a recognised accompaniment of cardiac events.