Sargia Harrison, being home-schooled at Kinross, asks :-

Why do we sweat mostly on our forehead and under our arms?

Richard Donald, an endochrinologist at the Christchurch School of Medicine, responded.

There are two sorts of sweat glands. The forehead and most of the body have eccrine glands, while the armpits, genital areas, nipples and scalp have larger apocrine sweat glands that are associated with hairs. The apocrine glands do not function until puberty. The question therefore makes an assumption which is not correct for young children, and which may not be correct for adults. We seem to sweat more from the forehead because the glistening sweat is more visible there, and from the armpits, because the apocrine secretion contains organic acids which are easy to smell.

The main function of sweat is to control body temperature through evaporation, and it can also affect the salt concentration in the body. Sweat may also contain pherormones which have a sex-attractant function. Although other primates may be able to detect them, humans cannot. Roald Dahl has written an entertaining short story on the commercial possibilities for such a pherormone. Sweat secretion is stimulated by hormones such as adrenaline and growth hormone, and also depends on a functioning autonomic nervous system.

Sweat secretion may be impaired in some diseases such as sugar diabetes, nervous system disorders, and exposure to radiation. The volume is increased by a rise in temperature, anxiety, flushing attacks and nocturnal sweating attacks during the change of life in women, excessive growth hormone or adrenaline secretion, sometimes from tumours, and the salt concentration is increased in cystic fibrosis.