Development and Growth
Hair follicles are to varying degrees sensitive to androgen, primarily testosterone and its derivatives, with different areas on the body having different sensitivity. As androgen levels increase, the rate of hair growth and the weight of the hairs increase. Genetic factors determine both individual levels of androgen and the hair follicle's sensitivity to androgen, as well as other characteristics such as hair colour, type of hair and hair retention.
Rising levels of androgen during puberty cause vellus hair to transform into terminal hair over many areas of the body. The sequence of appearance of terminal hair reflects the level of androgen sensitivity, with pubic hair being the first to appear due to the area's special sensitivity to androgen. The appearance of pubic hair in both sexes is usually seen as an indication of the start of a person's puberty. There is a sexual differentiation in the amount and distribution of androgenic hair, with men tending to have more terminal hair in more areas. This includes facial hair, chest hair, abdominal hair, leg and arm hair, and foot hair. Women retain more of the less visible vellus hair, although leg, arm, and foot hair can be noticeable on women. It is not unusual for women to have a few terminal hairs around their nipples as well. In the later decades of life, especially after the 5th decade, there begins a reduction in body hair especially marked in the legs. The reason for this is not known but it could be due to poorer circulation, lower free circulating hormone levels or other reasons.
Read more about this topic: Androgenic Hair
Famous quotes containing the words development and/or growth:
“I do seriously believe that if we can measure among the States the benefits resulting from the preservation of the Union, the rebellious States have the larger share. It destroyed an institution that was their destruction. It opened the way for a commercial life that, if they will only embrace it and face the light, means to them a development that shall rival the best attainments of the greatest of our States.”
—Benjamin Harrison (1833–1901)
“This [new] period of parenting is an intense one. Never will we know such responsibility, such productive and hard work, such potential for isolation in the caretaking role and such intimacy and close involvement in the growth and development of another human being.”
—Joan Sheingold Ditzion and Dennie Palmer (20th century)