Structure of the hair and hair follicle

The hair is made up of a protein called Keratin. The hair itself consists of 3 layers: the outer epidermis, the middle cortex and central medulla.

Pigments are also present in the hair dark (black or brown) or light (red or blond). When no pigments are present, the hair is white. Gray hair is actually an illusion due to a mixture of white and colored hair.

Hair grows from a hair follicle. The walls of the hair follicle form the outer root shafts of the hair. The lower part of the hair follicle is wider, to create the hair root, and contains the germinal matrix, the source of hair growth. Skin tissue snakes around the base of the hair follicle to form the dermal papilla. This has a network of hair blood vessels to transmit oxygen, energy and amino acids needed for growth. In the upper part of the papilla are so-called Melanocytes. They produce pigment granules that are distributed throughout the outer layer.

Inside the hair follicle, the hair is surrounded by an inner root shaft that has 3 layers.

The Henle layer (named after German physician Friedrich Gustav Jacob Henle): this is the third layer and lies against the outer root shaft. Then the Huxley layer (named after British physician Thomas Henry Huxley), this layer is 2 or 3 cells thick and lies in the middle of the shaft. The membrane of this inner root shaft interlocks with the membrane of the hair. Both the hair and this root shaft grow at the same rate but the root shaft breaks off from the hair follicle after ^2/3rds of the remote way. Thus, only the hair rises above the skin. Uncut hairs have a pointed end.

Hair growth cycle

Each hair follicle undergoes a circle of activity. The hair grows to a maximum length, stops and falls out and is replaced. At any given time we have only about 85% of our hair on our head, the rest is in resting phase. The hair growth cycle has 3 specific phases:

1. The anagen phase: the period of active growth.
2. The catagen phase: the period of failure and change.
3. The telogen phase: the resting phase before regrowth.

Anagen: The cells of the epidermis form the germinal matrix, or hair root. These cells constantly divide. As new cells form they push up the older ones and begin to change shape. When these cells are 1/3^e up from the follicle, they are dead and consist entirely of keratin. A head of hair actively grows between 1.5 and 7 years (3 years is an average growth period). The average growth rate is about 1 cm per month. About 85% of hair follicles are in the anagen phase.

Catagen: This is the end of the active growth period and is marked by changes in the hair follicles. The hair stops growing and detaches from the base of the hair follicle. The hair follicle begins to decompose and becomes smaller. A small portion of the outer root shaft remains in contact with the group of cells that form the papilla. This period of decomposition or change lasts about 3 weeks. When the inner root shaft decomposes, the hair remains in the hair follicle due to its shape. About 1% of hair follicles are in the catagen phase.

Telogen: The part of the remaining root shaft and still in contact with the papilla is known as the second or root germ. A new hair can grow from this germ. The smaller hair follicle rests for about 3 months. Now or at the beginning of the anagen phase, the hair can fall out by brushing. About 14% of hair follicles are in the telogen phase.

After the telogen phase, the anagen phase begins again and the radicle starts growing downward to form a new bulb around the dermal papillae. It is the lower part of the germ that forms a new bulb and produces a new hair. The upper part of the germ forms the new cells that extend the hair follicle under the hair. The new hair can push out the old one. This is why sometimes 2 hairs can be seen in the same hair follicle.

On average, one can lose between 60 and 100 hairs per day. If one loses more than 100 hairs per day, then hair loss will exceed replacement and you will eventually go bald. You may notice that hair loss in spring or fall is more than in summer. This is due to the daylight and weather.

In some people, the hair growth cycle does not (in both men and women). These people then remain virtually bald for 4 months and then the hair grows back as normal. Between the ages of ¹⁶ and ³⁰, hair grows fastest. New hair grows faster but the growth rate decreases as the hair grows longer. An adult has about an average of 100,000 hairs on the head. Blond people have more hair (about 140,000) and redheads have less (about 90,000).

That "your hairs will stand straight up," is not a joke. In fact, it really is. This is because the hair shaft contains small muscles called "arrectores pilonum". These contract under the influence of nervous excitement and cause the hair to become inflexible. It works just like the goose bumps you experience when you are cold.

This is another reason that hair is affected by your nervous system and the condition of your blood circulation. It is very strongly connected to the functioning of the entire human organism: body, mind and emotions.