Info

Dermal tissue Hair follicle

Hair root

Region of cell division

Hair papilla

Adipose tissue

Figure

(a) A hair grows from the base of a hair follicle when epidermal cells divide and older cells move outward and become keratinized.

(b) A light micrograph of a hair follicle (160x).

Keratinized cells of hair shaft

Squamous cells of epidermis

Figure

A scanning electron micrograph of a hair emerging from the epidermis (340x micrograph enlarged to 900x).

ure 6.7

Keratinized cells of hair shaft

Squamous cells of epidermis

Figure

A scanning electron micrograph of a hair emerging from the epidermis (340x micrograph enlarged to 900x).

Folliculitis is an inflammation of the hair follicles in response to bacterial infection. The condition can be picked up in dirty swimming pools or hot tubs. One woman got a severe case by repeatedly using a loofah sponge containing bacteria.

Usually a hair grows for a time and then rests while it remains anchored in its follicle. Later a new hair begins to grow from the base of the follicle, and the old hair is pushed outward and drops off. Sometimes, however, the hairs are not replaced. When this occurs in the scalp, the result is baldness, described in Clinical Application 6.2.

Genes determine hair color by directing the type and amount of pigment that epidermal melanocytes produce. For example, dark hair has much more melanin than blond hair. The white hair of a person with the inherited condition albinism lacks melanin altogether. Bright red hair contains an iron pigment (trichosiderin) that is not in hair of any other color. A mixture of pig-mented and unpigmented hair usually appears gray.

A bundle of smooth muscle cells, forming the arrector pili muscle (see figs. 6.2 and 6.6), attaches to each hair follicle. This muscle is positioned so that a short

Hair Loss

A healthy person loses from twenty to 1 00 hairs a day as part of the normal growth cycle of hair. A hair typically grows for two to six years, rests for two to three months, then falls out. A new hair grows in its place. At any time, 90% of hair is in the growth phase.

In the United States, about 57.5 million people have some degree of baldness. Pattern baldness, in which the top of the head loses hair, affects 35 million men and 20 million women. The women tend to be past menopause, when lowered amounts of the hormone estrogen contribute to hair loss, which is more even on the scalp than it is in men. Pattern baldness is called androgenic alopecia because it is associated with testosterone, an an-drogenic (male) hormone. About 2.5 million people have an inherited condition called alopecia areata, in which the body manufactures antibodies that attack the hair follicles. This results in oval bald spots in mild cases but complete loss of scalp and body hair in severe cases.

Various conditions can cause temporary hair loss. Lowered estrogen levels shortly before and after giving birth may cause a woman's hair to fall out in clumps. Taking birth control pills, cough medications, certain antibiotics, vitamin A derivatives, anti-depressants, and many other medications can also cause temporary hair loss. A sustained high fever may prompt hair loss six weeks to three months later.

Many people losing their hair seek treatment (fig. 6C). One treatment is minoxidil (Rogaine), a drug originally used to lower high blood pressure. Rogaine causes new hair to grow in 10 to 14% of cases, but in 90% of people, it slows hair loss. However, when a person stops taking it, any new hair falls out.

Hair transplants move hair follicles from a hairy part of a person's body to a bald part, and they are successful. Several other approaches, however, are potentially damaging — to the scalp. Suturing on hair pieces often leads to scarring and infection. The Food and Drug Administration banned hair implants of high-density artificial fibers because they too become easily in-

fected. Products called "thinning hair supplements" are conditioners, often found in ordinary shampoo, that merely make hair feel thicker. They are generally concoctions of herbs and the carbohydrate polysorbate. Labels claim the product "releases hairs trapped in the scalp." ■

Hair Loss Prevention

Hair Loss Prevention

The best start to preventing hair loss is understanding the basics of hair what it is, how it grows, what system malfunctions can cause it to stop growing. And this ebook will cover the bases for you. Note that the contents here are not presented from a medical practitioner, and that any and all dietary and medical planning should be made under the guidance of your own medical and health practitioners. This content only presents overviews of hair loss prevention research for educational purposes and does not replace medical advice from a professional physician.

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