Types of Hair

Knwoing what these words mean can help you better understand the articles on this website.

The below are quotes from Wikipedia

Terminal hair
Terminal hairs are thick, long, and dark, as compared with vellus hair.[1]  During puberty, the increase in androgenic hormone levels causes vellus hair to be replaced with terminal hair in certain parts of the human body.[2]  These parts will have different levels of sensitivity to androgens, primarily of the testosterone family.[3]

The pubic area is particularly sensitive to such hormones, as are the armpits which will develop axillary hair.[4] Pubic and axillary hair will develop on both men and women, to the extent that such hair qualifies as a secondary sex characteristic,[5] although males will develop terminal hair in more areas. This includes facial hair, chest hair, abdominal hair, leg and arm hair, and foot hair.[6] Human females on the other hand can be expected to retain more of the vellus hair.[7]

Vellus hair
Vellus hair, colloquially referred to as ‘peach fuzz’ or ‘bum fluff’ is short, fine, light-colored, and barely noticeable hair that develops on most of a person’s body from his/her childhood. Exceptions include the lips, the back of the ear, the palm of the hand, the sole of the foot, some external genital areas, the navel and scar tissue. The density of hair – the number of hair follicles per area of skin – varies from person to person. Each strand of vellus hair is usually less than 2 mm (1/13 inch) long and the follicle is not connected to a sebaceous gland.[1]

Vellus hair is most easily observed on children and adult women, as they generally have less terminal hair to obscure it. Vellus hair is not lanugo hair. Lanugo hair is a much thicker type of hair that, in human forms, normally grows only on fetuses.

Vellus hair is differentiated from the more visible terminal or androgenic hair, which develops only during and after puberty, usually to a greater extent on men than it does on women.

Lanugo Hair
Lanugo is fine, downy hair; it is a type of fur. Often found in teratomas.

Fetal development
Lanugo grows on fetuses as a normal part of gestation, but is usually shed and replaced by vellus hair at about 33 to 36 weeks of gestational age. As the lanugo is shed from the skin, it is normal for the developing fetus to consume the hair with the fluid, since it drinks from the amniotic fluid and urinates it back into its environment. Subsequently, the lanugo contributes to the newborn baby’s meconium. The presence of lanugo in newborns is a sign of premature birth.

Malnutrition
Lanugo can be observed in patients with eating disorders and the malnourished. When found along with other physical findings, lanugo can help a physician make a diagnosis of anorexia nervosa.[1]

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Androgenic hair
Androgenic hair, colloquially body hair, is the terminal hair that develops on the body during and after puberty. It is differentiated from the head hair and less visible vellus hair, which are much finer and lighter in color. The growth of androgenic hair is related to the level of androgens  (male hormones) in the individual. Due to a normally higher level of androgen, men tend to have more androgenic hair than women.

From childhood onward, regardless of gender, vellus hair covers almost the entire area of the human body. Exceptions include the lips, the backs of the ears, the palms of hands, the soles of the feet, certain external genital areas, the navel and scar tissue. The density of hair – the number of hair follicles per area of skin – varies from person to person. In many cases, areas on the human body that contain vellus hair will begin to produce darker, thicker body hair. An example of this is the growth of an adolescent’s beard on a once smooth chin.

Androgenic hair follows the same growth pattern as the hair that grows on the scalp, only the anagen phase is shorter, and the telogen phase is longer. While the anagen phase for the hair on one’s head lasts for years, the androgenic hair growing phase lasts a few short months [1]. The telogen phase for body hair lasts close to a year[1]. This shortened growing period and extended dormant period explains why the hair on the head tends to be much longer than other hair found on the body. Differences in length seen in comparing the hair on the back of the hand and pubic hair, for example, can be explained by varied growth cycles in those two regions. The same goes for differences in body hair length seen in different people, especially when comparing men and women

Sources:

http://en.wikipedia.org/wiki/Vellus_hair – Retrieved 1/2/2011

http://en.wikipedia.org/wiki/Androgenic_hair- Retrieved 1/2/2011

http://en.wikipedia.org/wiki/Terminal_hair- Retrieved 1/2/2011

http://en.wikipedia.org/wiki/Lanugo – Retrieved 1/2/2011

Image credits: wikipedia.org – Retrieved 1/2/2011






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