Hair IS...

Hair is far more complex than it appears on the surface. We all know that it not only plays a vital role in the appearance for both men and women. Hair also helps to transmit sensory information as well as create gender identification.

By week 22, a developing fetus has all of its hair follicles formed. At this stage of life there are about 5 million hair follicles on the body. There are a total of one million on the head, with one hundred thousand of those follicles residing on the scalp. This is the largest number of hair follicles a human will ever have, since we do not generate new hair follicles anytime during the course of our lives.

Most people will notice that the density of scalp hair is reduced as they grow from childhood to adulthood. The reason: Our scalps expand as we grow.

Hair Follicles

Hair has two distinct structures - the follicle and the shaft; the follicle resides in the skin and the shaft is is visible part above the scalp.

The hair follicle is a tunnel-like segment of the epidermis that extends down into the dermis. The structure contains several layers that all have separate functions. At the base of the follicle is the papilla, which contains capillaries, or tiny blood vessels that nourish the cells. The living part of the hair is the very bottom part surrounding the papilla, called the bulb. The cells of the bulb divide every 23 to 72 hours, remarkably faster than any other cell in the body. Two sheaths, an inner and outer sheath, surround the follicle. These structures protect and form the growing hair shaft. The inner sheath follows the hair shaft and ends below the opening of a sebaceous (oil) gland, and sometimes an apocrine (scent) gland. The outer sheath continues all the way up to the gland. A muscle called an erector pili muscle attaches below the gland to a fibrous layer around the outer sheath. When this muscle contracts, it causes the hair to stand up which also causes the sebaceous gland to secrete oil.

The sebaceous gland is vital because it produces sebum, which conditions the hair and skin. After puberty our body produces more sebum but as we age we begin to make less sebum. Women have far less sebum production than men do as they age.

The word "alopecia" is the medical term for hair loss. Alopecia does not refer to one specific hair loss disease but rather any form of hair loss can be classified as alopecia. Hair loss can be caused by any number of conditions, reflected in a specific diagnosis. Some diagnoses have alopecia in their title, such as alopecia areata or scarring alopecia, but many do not, such as telogen effluvium.

Alopecia can be caused by many factors from genetics to drugs. While androgenetic alopecia (male or female pattern baldness, AGA for short) is by far the most common form of hair loss, dermatologists also see many people with other forms of alopecia. Several hundred diseases have hair loss as a primary symptom.

Probably the most common non-AGA alopecias a dermatologist will see are telogen effluvium, alopecia areata, ringworm, scarring alopecia and hair loss due to cosmetic overprocessing. Other, more rare forms of hair loss may be difficult to diagnose and some patients may wait months even years for a correct diagnosis and must undergo consultation with numerous dermatologists until they find one with knowledge of their condition. Plus, with rare diseases, there is little motivation for research to be conducted and for treatments to be developed. Often, even when a correct diagnosis is made, a dermatologist can offer no known treatment for the condition. Hair diseases is a very small field and even research on androgenetic alopecia is quite limited. Perhaps 20 years ago there were fewer than 100 people worldwide who studied hair research in a major way. In recent years, there may be five times as many. This is still a small number compared to, say, diabetes research, but the expanding numbers of researchers investigating hair biology is positive and eventually should lead to a better understanding and more help for those with rare alopecias.

The hair shaft is made of a hard protein called keratin and is made in three layers. This protein is actually dead, so the hair that you see is not a living structure. The inner layer is the medulla. The second layer is the cortex and the outer layer is the cuticle. The cortex makes up the majority of the hair shaft. The cuticle is a tightly formed structure made of shingle-like overlapping scales. It is both the cortex and the medulla that holds the hair's pigment, giving it its color.

Hair Growth Cycle

Hair on the scalp grows about .3 to .4 mm/day or about 6 inches per year. Unlike other mammals, human hair growth and shedding is random and not seasonal or cyclical. At any given time, a random number of hairs will be in one of three stages of growth and shedding: anagen, catagen, and telogen.

• Anagen

  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.

• Catagen

  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 a club hair.

• Telogen

  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.