The skin of an adult weighs an average of 4kg/9lb, and covers an area of 2 square metres (22 sq ft). But although skin might look like a simple layer, it is, in fact made up of many layers with all kinds of things embedded in it, such as places where hair grows and places from which we sweat.

The skin not only protects the rest of the body from bashes and scrapes with the outside world, it is also the first line of defence from disease. It also stops the body from losing too much water. Without skin, we would have to keep drinking all the time, as our internal organs have no means of stopping water evaporating. But the skin does even more. Its thick fatty surface layers stop too much heat getting to our internal organs when it is hot, and too much heat being lost when it is cold. And it does yet more. It has tiny sensors all over it that give us our sense of touch.

Given how important skin is, you will not be surprised to know that the body has all kinds of ways of repairing it quickly should it ever be damaged, say by a cut.

Skin is not one thickness all over our bodies either. It is paper thin around our eyes and over our eyelids. It is about 0.5 mm thick, whereas the skin on the palms of the hands and the soles of the feet is 4 mm thick, in part because these parts get the most battering. And that brings us on to the last important purpose of skin. Because it is made of fat, and fat is a very concentrated form of energy, the body stores the reserves it needs as fat. As the body is covered in a layer of fatty skin, the skin is where much of the body fat is kept. So if we eat more than the body needs it just tells it to spread it around the skin, and the skin gets thicker.

The skin is also oily. It needs to be that way. Tiny amounts of oils are released from little tubes called glands.

The skin is made of two main layers. The one you see is called the epidermis and below it is the thicker dermis.