The surface of every part of the body, inside and out, is covered with a protective layer, or layers, of tightly packed cells called epithelia. The largest, thickest and most complex of these epithelial tissues is the skin which covers the whole of the outside of the body. The skin itself is made of two principal layers. The outer layer – the part of the skin we actually see – is called the epidermis. The softer, more delicate inner layer is the dermis.
It is in the dermis that the roots of the hair are contained. In other mammals the hair is farmore important than in man. It helps to regulate the heat of the body. In cold conditions the skin tightens. This raises the hair from the surface of the skin and creates an insulating layer of air which helps the body retain its heat. In cold weather our own skin still behaves in the same instinctive way and we experience what is known as ‘goose flesh’, or ‘goose pimples’.
When the body needs to lose heat rather than retain it the sweat glands starts to function. Sweat is largely water, and as it comes to the surface of the skin through the sweat glands it carries with it excess body heat which then evaporates into the surrounding air, thus acting as a method of cooling.