GrowthDistribution of androgenic hair on female and male body
Different parts of the human body feature different types of hair. From childhood onward, vellus hair covers the entire human body regardless of sex or race except in the following locations: The lips, the nipples, the palms of hands, the soles of feet, certain external genital areas, the navel, and scar tissue. The density of the hairs (in hair follicles per square centimeter) varies from one person to another.
The rising level of male hormones (androgens) during puberty causes a transformation process of vellus hair into terminal hair on several parts of the male body. The hair follicles respond to androgens, primarily testosterone and its derivatives; the hair in these locations can be thus termed androgenic hair. The rate of hair growth and the weight of the hairs increase. However, different areas respond with different sensitivities. As testosterone levels increase, the sequence of appearance of androgenic hair reflects the gradations of androgen sensitivity. The pubic area is most sensitive, and heavier hair usually grows there first in response to androgens.Layers of an individual hair
Areas on the human body that develop terminal hair growth due to rising androgens in both sexes, men and women, are the underarms and the pubic area. In contrast, normally only men grow androgenic hair in other areas. There is a sexual dimorphism in the amount and distribution of androgenic hair, with males having more terminal hair (particularly facial hair, chest hair, abdominal hair, and hair on legs and arms) and females having more vellus hair, which is less visible. The genetic disposition determines the sex-dependent and individual rising of androgens and therefore the development of androgenic hair.
Increased body hair on women following the male pattern can be referred to as hirsutism. An excessive and abnormal hair growth on the body of males and females is defined as hypertrichosis. Considering an individual occurrence of body hair as abnormal does not implicitly depend on medical indications, but also on cultural and social attitudes.
Individual hairs alternate periods of growth and dormancy. During the growth portion of the cycle, hair follicles are long and bulbous, and the hair advances outward at about a third of a millimeter per day. After three to six months, body hair growth stops (the pubic and armpit areas having the longest growth period), the follicle shrinks, and the root of the hair grows rigid. Following a period of dormancy, another growth cycle starts, and eventually a new hair pushes the old one out of the follicle from beneath. Head hair, by comparison, grows for a long duration and to a great length before being shed. The rate of growth is approximately 15 millimeters, or about ⅝ inch, per month.A stylized photo of curly hair
Hair texture is measured by the degree of which one's hair is either fine or coarse, which in turn varies according to the diameter of each individual hair. There are commonly four major categories recognized for hair texture: Fine, medium, coarse, and wiry. Within the four texture ranges hair can also have thin, medium, or thick density and it can be straight, curly, wavy, or kinky. Hair conditioner will also alter the ultimate equation. Hair can also be textured if straighteners, crimpers, curlers, and so forth are used to style hair. Also, a hairdresser can change the hair texture with the use of special chemicals.
According to Ley (1999), the diameter of human hair ranges from 17 to 181 µm (millionths of a meter).
Older people tend to develop gray hair because the pigment in the hair is lost and the hair becomes colorless. Gray hair is considered to be a characteristic of normal aging. The age at which this occurs varies from person to person, but in general nearly everyone 75 years or older has gray hair, and in general men tend to become gray at younger ages than women.
It should be noted however, that gray hair in itself is not actually gray. The gray head of hair is a result of the contrast between the dark and the white/colorless hair forming an overall "gray" appearance to the observer. As such, people starting out with very pale blond hair usually develop white hair instead of gray hair when aging. Red hair usually does not turn gray with age; rather it becomes a sandy color and afterward turns white. In fact, the gray or white appearance of individual hair fibers is a result of light scattering from air bubbles in the central medula of the hair fiber.
Some degree of scalp hair loss or thinning generally accompanies aging in both males and females, and it is estimated that half of all men are affected by male pattern baldness by the time they are 50 (Springfield 2005). The tendency toward baldness is a trait shared by a number of other primate species, and is thought to have evolutionary roots.
It is commonly claimed that hair and nails will continue growing for several days after death. This is a myth; the appearance of growth is actually caused by the retraction of skin as the surrounding tissue dehydrates, making nails and hair more prominent.
Pathological impacts on hair
Drugs used in cancer chemotherapy frequently cause a temporary loss of hair, noticeable on the head and eyebrows, because they kill all rapidly dividing cells, not just the cancerous ones. Other diseases and traumas can cause temporary or permanent loss of hair, either generally or in patches.
The hair shafts may also store certain poisons for years, even decades, after death. In the case of Col. Lafayette Baker, who died July 3, 1868, use of an atomic absorption spectrophotometer showed the man was killed by white arsenic. The prime suspect was Wally Pollack, Baker's brother-in-law. According to Dr. Ray A. Neff, Pollack had laced Baker's beer with it over a period of months, and a century or so later minute traces of arsenic showed up in the dead man's hair. Mrs. Baker's diary seems to confirm that it was indeed arsenic, as she writes of how she found some vials of it inside her brother's suit coat one day.
Head hairPeople from different cultures have invented various ways to arrange, or "style," their hair.
The remarkable head hair of humans has gained an important significance in nearly all present societies as well as any given historical period throughout the world. The haircut has always played a significant cultural and social role.
In ancient Egypt, head hair was often shaved, especially among children, as long hair was uncomfortable in the heat. Children were often left with a long lock of hair growing from one part of their heads, the practice being so common that it became the standard in Egyptian art for artists to depict children as always wearing this "sidelock." Many adult men and women kept their heads permanently shaved for comfort in the heat and to keep the head free of lice, while wearing a wig in public.
In ancient Greece and ancient Rome, men and women already differed from each other through their haircuts. The head hair of a woman was long and generally pulled back into a chignon hairstyle. Many dyed their hair red with henna and sprinkled it with gold powder, often adorning it with fresh flowers. Men's hair was short and even occasionally shaved. In Rome, hairdressing became ever more popular and the upper classes were attended to by slaves or visited public barber shops.Maasai warriors with their traditional hair styling
The traditional hair styling in some parts of Africa also gives interesting examples of how people dealt with their head hair. The Maasai warriors tied the front hair into sections of tiny braids, while the back hair was allowed to grow to waist length. Women and non-warriors, however, shaved their heads. Many tribes dyed the hair with red earth and grease; some stiffened it with animal dung.
Contemporary social and cultural conditions have constantly influenced popular hair styles. From the seventeenth century into the early nineteenth century, it was the norm for men to have long hair, often tied back into a ponytail. Famous long-haired men include Oliver Cromwell and George Washington. During his younger years, Napoleon Bonaparte had a long and flamboyant head of hair. Before World War I, men generally had longer hair and beards. The trench warfare between 1914 and 1918 exposed men to lice and flea infestations, which prompted the order to cut hair short, establishing a norm that has persisted.
However it has also been advanced that short hair on men has been enforced as a means of control, as shown in the military and police and other forces that require obedience and discipline. Additionally, slaves and defeated armies were often required to shave their heads, in both pre-medieval Europe and China.
Growing and wearing long hair is a lifestyle practiced by millions worldwide. It was almost universal among women in Western culture until World War I. Many women in conservative Pentecostal groups abstain from trimming their hair after conversion (and some have never had their hair trimmed or cut at all since birth). The social revolution of the 1960s led to a renaissance of unchecked hair growth.
Hair length is measured from the front scalp line on the forehead, up over the top of the head and down the back to the floor. Standard milestones in this process of hair growing are classic length (midpoint on the body, where the buttocks meet the thighs), waist length, hip length, knee length, ankle/floor length, and even beyond. It takes about seven years, including occasional trims, to grow one's hair to waist length. Terminal length varies from person to person according to genetics and overall health.
Body hairA human male with body hair.
The attitudes towards hair on the human body also vary between different cultures and times. In some cultures, profuse chest hair on men is a symbol of virility and masculinity; other societies display a hairless body as a sign of youthfulness.
In ancient Egypt, people regarded a completely smooth, hairless body as the standard of beauty. An upper class Egyptian woman took great pains to ensure that she did not have a single hair on her body, except for the top of her head (and even this was often replaced with a wig (Dersin 2004). The ancient Greeks later adopted this smooth ideal, considering a hairless body to be representative of youth and beauty. This is reflected in Greek female sculptures which do not display any pubic hair. Islam stipulates many tenets with respect to hair, such as the covering of hair by women and the removal of armpit and pubic hair.
In Western societies, it became a public trend during the late twentieth century, particularly for women, to reduce or to remove their body hair.
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