Sweat is a salty liquid made in curly glands deep in the dermis. It oozes to the surface through tiny holes, called pores. As it dries, or evaporates, it draws warmth away from your body and cools you down. You have over 3 million sweat glands. Even on a cool day, you lose 0.3 litres (0.5 pints) of sweat. This rises to 2 litres (3.5 pints) on a hot day.