Apart from being useful for elevating, furrowing, and piercing, the hair on your brows keeps sweat out of your eyes. And your hair protects your head from the direct rays of the sun. It also creates a space between your scalp and the heated surface of your hair, allowing perspiration to drain and cool things down. Finally, hair helps prevent injury to the brain due to pressure from the skull. Hair grows as cells called follicles reach maturity and develop hooks that attach them to the skin. As these loops pull up on the skin's surface, more cells are produced to fill in the gap. This process continues until the skin is no longer able to produce new cells or the follicle detaches from the bone that it comes attached to. After this point, the hair will begin to come out naturally. On average, men have about 100,000 hairs per square inch while women have around 250,000. The number of hairs you have isn't always the same as the number of people who live there because some of them may be dead hairs that fall out. Some people lose hairs due to aging or illness. Most often, though, people lose their hairs because they go away for a vacation or move to another city. In general, if you're healthy and you eat a balanced diet with plenty of fruits and vegetables, you should be growing your own hair too.