Sweat is a watery fluid containing between \(0.1 \%\) and \(0.4 \%\) of sodium chloride, sodium lactate (from lactic acid) and urea. In deep mines the worker's body temperature rises above its mean value of \(36.7^{\circ} C\) causing the sweat glands (eccrine and apocrine) to release sweat to the skin. The sweat then evaporates from the skin surface; energy is lost from the bady as latent heat of evaporation and this reduces body temperature.