Hair grows out of tiny pits in the skin. Each hair has a kind of root which is fed from blood vessels in the skin. Hair grows, matures and dies. It then falls out and is replaced by a newly growing hair. This does not happen to all hairs all over the body at the same time, but each hair behaves independently, so that you do not notice the change except that you may find hairs on your shoulders just after they have fallen out, or in your hairbrush.

Hairs have a number of uses. They provide a means of sensing things around. If you brush the hairs on your arms you will feel it. That is why animals such as dogs have long hairs around their snouts.

When it is cold, hairs stand on end and help to trap air, which insulates the body a little. They stand on end because the skin changes - we call it 'goose bumps'.

Hair grows to different lengths in different parts of the body. It can grow to tens of centimetres long on the head and (in men) chin and this gives a chance for us to decide how to change it. The changes we create is called hairdressing.

Hairs not only provide a way of trapping air, they also provide a home to many bugs, such as hair lice. Hair lice are not good news, and if nothing else, they feel itchy. They can, however, also spread disease. This is why it is important to wash hair with special shampoo regularly.

Your head contains 100,000 hairs. Their combined growth each year is about 10km. No wonder you need a haircut from time to time. But if you didn't have one, your hairs would fall out naturally after a while. Not all at the same time, of course.

Hair is definitely dead. When it leaves the growth points in the skin, it is already dead. It is simply a natural fibre containing keratin (the same stuff nails are made from) and also melanin, which gives colour. It is very strong and quite elastic, but gets weaker in sunlight, which is why the ends are weakest.

To make hair feel shiny, or to make it bulk up, hair treatments usually coat the hairs with slippery oil or plastic. It's often called 'conditioner'. Some chemicals get inside the hair fibre and make it bulkier that way.