< previous page | page_41 | next page >
Page 41
| The Hair |
| Hair can add to our beauty, our individuality, keep our heads warm and protect from the elements and injury. |
| Since hair doesn't contain any nerves, it is considered nonliving tissue. One of the main components of hair is the fibrous protein, keratin, which is made of 18 amino acids. Keratin is in a doublehelix formation. A single strand of hair can last from two to four years. The average scalp has a total of 100,000 hairs. Below the scalp is the funnel-shaped hair follicle containing a sebaceous gland that makes the oily substance, sebum. It is the follicle's shape that determines whether the hair will be straight or curly. At the end of the follicle is a bulb known as the papilla. It is through this opening that hair receives nutrients through the bloodstream. Each hair has a medulla or hollow inner core and a cuticle which is an outer protective layer. The health of the hair can be a reflection of one's general state of vitality. It is normal to lose about 75 hairs a day. Most hair tends to be thicker in the summer and to fall out more in autumn. About 90 percent of the hair is growing (anagen phase) and 10 percent is at the resting stage (telogen phase). When new hair pushes out the old hair this is the catagen phase. |
| Hair usually grows one half-inch per month; it grows the fastest between the ages of 15 and 30. After age 50 hair growth will slow down somewhat. In the average lifetime, hair will grow about 25 feet. When hair grows, new cells overlap the older cells. |
< previous page | page_41 | next page >

If you like this book, buy it!