Hair is made of two structures, the first one is the follicle, located in the skin, the second, is the shaft, is what you see on your scalp. The hair follicle is like a tunnel or a straw. The epidermis extends down into the dermis. The follicle has several layers that serve different purposes. The base of the follicle is called the papilla, the papilla contains capillaries, or tiny blood vessels. This is the only living part of the hair. These blood vessels are located at the very bottom part surrounding the papilla, called the bulb. The cells of the bulb divide remarkably faster than any other cell in the body, on the average every 23 to 72 hours. There are two layers that surround the follicle, the inner and outer. These structures protect the growing hair shaft. The inner layer guides the hair shaft and ends below the opening of a sebaceous gland. The outer layer continues all the way up to the gland. The sebaceous gland is vital because it produces sebum, which conditions the hair and skin. As we age, the production of sebum begins to slow down.
The hair shaft is made of a protein called keratin. Keratin is made up of three layers; the inner-most layer is the medulla, the cortex is the middle layer and the cuticle is the outer-most layer. The cortex makes up the majority of the hair shaft. The cuticle is a tightly formed structure made of tiny scales-like structures that line the outer part of the hair protecting the inner parts of the hair. The cortex and the medulla together makes up the hair’s pigment, giving it its color. **Hair needs both protein and moisture to survive. This is why it is important to deep condition your hair using both protein and moisture products.**
Hair Growth Cycle
Hair on the scalp grows about ½ an inch a month or about 6 inches a year. Our hair sheds naturally. Our hair is in a constant stage of growing, a stage of transition, and a stage of shedding. These stages are called Angen (growing), Catagen (transition), and Telogen (shedding)
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- Anagen is the active phase of the hair. The cells in the root of the hair are dividing rapidly. A new hair is formed and pushes the club hair (a hair that has stopped growing or is no longer in the anagen phase) up the follicle and eventually out. During this phase the hair grows about 1 cm every 28 days. Scalp hair stays in this active phase of growth for two to six years. Some people have difficulty growing their hair beyond a certain length because they have a short active phase of growth. On the other hand, people with very long hair have a long active phase of growth. The hair on the arms, legs, eyelashes, and eyebrows have a very short active growth phase of about 30 to 45 days, explaining why they are so much shorter than scalp hair.
- The catagen phase is a transitional stage and about 3% of all hairs are in this phase at any time. This phase lasts for about two to three weeks. Growth stops and the outer root sheath shrinks and attaches to the root of the hair. This is the formation of what is known as the club hair.
- Telogen is the resting phase and usually accounts for 6% to 8% of all hairs. This phase lasts for about 100 days for hairs on the scalp and longer for hairs on the eyebrow, eyelash, arm, and leg. During this phase, the hair follicle is completely at rest and the club hair is completely formed. Pulling out a hair in this phase will reveal a solid, hard, dry, white material at the root. About 25 to 100 telogen hairs are shed normally each day.