Sweat cools the body by evaporating from the skin and carrying heat away.

The longer version

Evaporation removes heat because turning a liquid into vapour requires energy, and that energy is taken from the skin underneath. Sweat glands release a watery fluid onto the surface, and as it spreads and turns to vapour, the skin loses warmth without any change in air temperature.

Glands are distributed over most of the body, with dense clusters on the palms, soles and forehead. The fluid itself is nearly pure water with small amounts of salts. Humid air slows the process because the surrounding air already holds moisture, which is why the same heat feels very different in dry and sticky conditions.

Where this entry sits

These facts look at how the human body works in ordinary moments, from breathing and blinking to balance and sleep. They focus on anatomy, senses, and small reactions that happen constantly without any conscious effort. The full list sits on the Human Body page, where every entry is listed in order.