Everything about Body Hair totally explained
Androgenic hair, colloquially
Body hair, is the
terminal hair on the
human body developed during and after
puberty. It is differentiated from the head
hair and less visible
vellus hair.
Androgenic denotes its growth is related to the level of
androgens (male
hormones) in the individual. Due to a normally higher level of androgens,
men tend to have more androgenic hair than
women.
From
childhood onward, regardless of
sex,
vellus hair covers the entire 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 (
hair follicles per
square centimeter) varies from one person to another.
Development and growth
Rising levels of
androgens during puberty cause
vellus hair to transform into
terminal hair over many areas of the body.
Hair follicles respond to androgens, primarily
testosterone and its derivatives. Different areas respond with different sensitivities. The rate of hair growth and the weight of the hairs increase. The sequence of appearance of androgenic hair reflects the gradations of androgen sensitivity. Since the pubic area is most sensitive, heavier hair usually grows there first. Genetic factors determine both individual levels of androgens and the hair follicle's sensitivity to androgens, and thus hair development.
Most noticeable in both sexes are the development of
axillary hair and
pubic hair. Thus it's sometimes viewed as a
secondary sex characteristic. There is a
sexual differentiation in the amount and distribution of androgenic hair, with males having more terminal hair in more areas. This includes
facial hair,
chest hair,
abdominal hair,
leg and
arm hair, and
foot hair. Females retain more of the less visible
vellus hair, though
leg,
arm, and
foot hair is noticeable.
Evolution
Evolutionary and genetic evidence suggests human androgenic hair is the remnant of body hair of the type found on today's
great apes. Full-on body hair phased out in the course of
human evolution roughly 2-3 million years ago. Loss of body hair is related to several unique aspects of human evolution. Homo Erectus, and later pre-modern humans, began relying on sweating for
thermoregulation instead of insulating hair. Because of the intensity of sunlight, and harmful ultraviolet radiation, loss of hair put positive selective pressures on development of protective dark
skin colour. Based on the numbers and spread of variations in the
MC1R nucleotide sequences between humans and chimpanzees, modern hair patterns were seen by 1.2 million years ago. However, hair densities and patterns on humans differ for populations in differing climates.
Further Information
Get more info on 'Body Hair'.
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