Sweat Glands and Thermoregulation
Sweat Glands and Thermoregulation — structures in the skin that produce sweat, which cools the body as it evaporates from the surface. This process is the main way skin helps maintain a stable internal temperature during heat or exertion.
Key points
- Eccrine glands are found across most of the body and produce the watery sweat used primarily for cooling.
- Apocrine glands, concentrated in areas like the armpits, produce a thicker secretion associated with body odor when broken down by bacteria.
- Sweat cools the body through evaporation, drawing heat away from the skin surface.
- The nervous system controls sweating in response to temperature, exercise, and emotional stress.
Eccrine and apocrine side by side
| Feature | Eccrine | Apocrine |
|---|---|---|
| Where they are | Almost all skin; densest on palms, soles, forehead | Underarms, groin, areolae, ear canal |
| How many | Roughly two to four million | Far fewer, and only at those sites |
| Where they open | Onto the surface, through their own pore | Into a hair follicle, above the sebaceous duct |
| Active from | Infancy | Puberty, under hormonal influence |
| What they secrete | Dilute and watery: water, salt, lactate, urea | Thicker and milky: proteins, lipids, steroids |
| Main role | Evaporative cooling and temperature control | Not thermoregulatory; scent-related, poorly understood |
| Main trigger | Core and skin temperature, exercise | Emotional stress and adrenaline |
What sweat is actually made of
Eccrine sweat leaves the secretory coil close to plasma in composition, but the duct reabsorbs much of the sodium and chloride on the way up. What reaches the surface is dilute — around 99 per cent water, with salt, lactate, urea and potassium, plus traces of antimicrobial peptides. Saltiness varies with sweat rate and with how heat-acclimatised a person is.
That is worth stating plainly because of a persistent misconception: sweating is not a route of detoxification. Anything beyond water and salts appears only in trace quantities, and clearing metabolic waste is the work of the liver and kidneys. What sweating achieves is temperature control, which is no small job — it is why humans tolerate sustained exertion in heat.
Why evaporation, not sweat itself, does the cooling
The body sheds heat by radiation, conduction and convection, but those routes stall as the surrounding air approaches skin temperature. Evaporation still works. Turning liquid water into vapour absorbs a large amount of energy, drawn from the skin it leaves behind. Sweat that rolls off, or is wiped away before it evaporates, has cooled almost nothing.
This is why humidity matters. In humid air, evaporation slows and sweat accumulates without cooling, so the same temperature feels far more punishing. Repeated heat exposure produces acclimatisation over a week or two: people sweat sooner, more evenly and with less salt lost. Rates vary widely with fitness, body size and conditions, so fluid replacement matters during prolonged heat.
Odour, and sweat's part in the acid mantle
Freshly secreted sweat is essentially odourless. Apocrine secretion is richer in proteins and lipids, and it is the skin's resident bacteria — corynebacteria and staphylococci in particular — that break those molecules into the volatile acids and sulphur compounds recognised as body odour. That is why underarm odour builds over hours rather than appearing the moment you sweat.
Sweat also feeds the acid mantle, the thin acidic film on the surface. Lactate and amino acids in eccrine sweat, with free fatty acids from sebum and breakdown products from the stratum corneum, help hold surface pH in a mildly acidic range of roughly 4.5 to 5.5. Lactate is also part of natural moisturising factor. Salt left drying on skin, though, can feel tight.
Frequently asked
How does sweating actually cool me down?
As sweat evaporates from the skin's surface, it absorbs heat and carries it away, which lowers skin and body temperature.
Why do I sweat more in some areas than others?
Sweat glands are unevenly distributed, so regions like the palms, forehead, and underarms have higher gland density and tend to sweat more noticeably.
Does sweating remove toxins from the body?
No. Sweat is overwhelmingly water and salts, with only trace amounts of anything else. Clearing metabolic waste is the job of the liver and kidneys.
Why does sweat smell if it is mostly water?
It does not smell when secreted. Odour develops as skin bacteria break down the proteins and lipids in apocrine secretion into volatile compounds, mainly in the underarms and groin.
Is sweating a lot a sign that something is wrong?
Usually not, since sweat rates differ widely with fitness, acclimatisation and body size. Sweating that is excessive for the situation, one-sided, or newly changed is described as hyperhidrosis and is worth raising with a clinician.
Can sweat cause breakouts?
Sweat itself does not block follicles. Heat, friction and moisture trapped under tight clothing or equipment can irritate skin and inflame follicles, which is why the pattern often follows straps and seams.
Related topics
This is a foundational entry in the SYNC Skin Encyclopedia and is expanded over time. Educational information only — not medical advice.
