About Hair Loss

Part Two

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The amount of hair and where itgrows vary with different mammals. The entire body of the dog, the sheep, thecow, and the horse is covered with a hairy coat. The whale and the hippopotamushave only a few hairs. In humans, hair is not found on palms of the hands or thesoles of the feet.
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The coloration and pattern of coatsin animals serve both as a camouflage for protection against enemies and as anallurement to mates. Fine and transparent, human hair is a vestige of ourhairier animal forbears, that probably evolved from the scales of reptiles. Theadult human body averages five million hairs, of which 100,000 to 150,000 are onthe scalp.

Hair is composed of keratin, thesame protein that makes up nails and the outer layer of our skin. The part seenrising out of the skin is called hair shaft or strand. Each strand consist ofthree layers. The outermost protective layer (cuticle) is thin and colorless.The middle layer, or cortex , is the thickest. It provides strength, determinesyour hair color and whether your hair is straight or curly.

Hair color is determined by melaninfrom your pigment cells. The more pigment granules there are, and the moretightly packed, the darker the hair. Two kinds of melanin contribute to haircolor. Eumelanin colors hair brown to black, and an iron-rich pigment,pheomelanin colors it yellow-blonde to red. Whether hair is mousy, brown,brunette or black depends on the type and amount of melanin and how densely it'sdistributed within the hair. For example, deep-black African hair containsclosely packed melanin in the cortex, a few in the cuticle. Very dark Europeanhair, quite apart from having more melanin granules than lighter or blonde hair,has more melanin per granule. When pigment-producing cells cease to function,the result is the uncolored white or gray hair.

Scalp hair varies tremendouslybetween races, between individuals of same race, and even within an individual.Mongolians have straight hair simply because their scalp hair has the greatestthickness and the roundest cross-section. In Caucasians the hair is moreelliptical and slender; in African Americans it is flattened, resulting in kinky curls.Mongolians, both male and female, have much less public, axillary, facial, andbody hair than Caucasians. In Caucasians, true blonds typically have more hair(about 140,000 hair) than brunette (about 105,000) or redhead (about 90,000).

Below your skin is the hair rootwhich is enclosed by a sack-like structure called the hair follicle. Tiny bloodvessels at the base of the follicle provide nourishment. A nearby gland secretesa mixture of fats (called sebum) which keep the hair shiny and waterproof tosome  extent. Secretions from some sweat glands also produce acharacteristic odor. A dog can differentiate a human being by the typical scentsecreted by these glands. Two sets of glands discharge secretions through theskin. while sebaceous, or oil, glands arise from the walls of hair follicles andproduce an oil called sebum that lubricates the skin and hair, Sweat glands,embedded in the subcutaneous layer, are scattered over the body, particularly inthe palms and soles. Sweat glands produce moisture called perspiration thatreaches the skin's surface through the pores and evaporates to cool the body.
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At the base of the follicle is thepapilla, which is the "hair manufacturing plant." The papilla is fedby the blood-stream which carries nourishment to produce new hair. Male hormonesor androgens regulate hair growth. Pubic and axillary (armpit) hair areparticularly androgen-sensitive and grow at lower androgen levels than hair onthe chest or legs. In boys, most pubic hair is grown by age 15, followed by thedevelopment of armpit hair two to three years later. In girls, too, an increasein androgens at puberty triggers growth of pubic and armpit hair. Scalp hair,not directly androgen-responsive, is influenced by local amounts of atestosterone derivative, dihydrotestosterone.

Hair follicles initially form inutero. No new follicles are created after birth, and none are lost in adultlife. The first hair to be produced by the fetal hair follicles is Lanugo hair,which is fine, soft, and unpigmented. This is usually shed in about the eighthmonth of gestation.

The first postnatal hair is vellushair, which is fine, soft, usually unpigmented, and seldom more than 2 cm long.Vellus hair remains on the so-called hairless regions of the body, such as theforehead and balding scalp. At puberty, the vellus hair in some areas isreplaced by terminal hair, which is longer, coarser, and pigmented. Growthstarts in the pubic region; then the eyelashes and eyebrows become thicker.Axillary hair and male facial hair appear about two years after growth of pubichair begins. Body hair continues to develop long after puberty, stimulated bymale hormones that paradoxically, also cause terminal hair to be replaced byvellus hair when balding begins.

Scalp hair fibers grow from 100,000to 350,000 follicles which are reported to occupy the human scalp; however, notall the follicles are productive.[1] In each producing follicle, the duration ofthe hair's life cycle is influenced by age, pathology and a wide variety ofphysiological factors. [1,2] The life cycle is divided into the anagen (active),catagen (transitional) and telogen (resting) phases.

The anagen phase is the period ofactive hair growth where protein synthesis and keratinization are continuouslyoccurring. In normal subjects, this phase lasts for up to five years, althoughlonger durations have been documented.

The cessation of the anagen phase ischaracterized by a transitory phase known as catagen. This phase lasts for twoto three weeks. Following the catagen phase, the hair enters the telogen or"resting" phase. In normal subjects, telogen hair is retained withinthe scalp for up to 12 weeks before the emerging new hair dislodges it from itsfollicle.

During the anagen phase, protein sthesis is the main distinction of the hair bulb. In the telogen phase, thedermal papilla undergoes renewal. It is at this time that structuralcharacteristics can be modified. The new hair should be identical to itspredecessor, but with advancing age, and in some pathological states, a strictcopy is not maintained. In these circumstances, the hair may become finer andshorter, modifying the esthetic profile. Since these effects occur over severalhair cycles, years may elapse before the affected individual recognizes thedifference.

Like skin cells, hair grows and isshed regularly. Shedding anywhere from 50 to 100 hairs per day is considerednormal. The average rate of growth is about 1/2 inch a month. It is now knownthat hair grows fastest in the summer, slowest in the winter, speeds up underheat and friction, but slows down when exposed to cold. Hair grows the bestbetween the ages of 15 to 30. But, hair growth begins to wind down sometimebetween the ages of 40 and 50. Progressive hair loss begins naturally in bothsex about age 50, accelerating in the 70s. About 40 percent of Caucasian menlose hair to some extent by age 35.

What cause hair loss? can we dosomething about it?
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(click here for part one - hair loss)