Puberty and Hair
A: None. We as humans normally have the same number of hair follicles as an infant as we do as adults. The difference is the types of hair produced by these follicles.
The hair found on the top, back and sides of the head that are generally darker, longer and thicker are known as terminal hairs. Vellus hairs are the most prevalent hairs found on pre-puberty individuals, who typically have terminal hairs only on the head.
As we grow and age, some of the hairs of our body will change as we enter puberty and our body produces the hormones that cause the secondary sexual characteristics to develop. These hormones trigger changes in the follicles on certain areas of the body (the backs of the arms, the groin, and the armpits in boys and girls, as well as the face in boys). The vellus hairs that were there before suddenly start growing thicker, darker and may even become curlier.
Even later in the aging process, men and women can experience changes in the way the hair follicles behave as a result of hormonal changes. Men may develop male pattern baldness, and women may experience the development of facial hair. Most of these changes are normal and occur on a schedule that varies from person to person but generally follows a set pattern.
However, when an individual experiences change in the hair that grows on the body or head that isn't normal for his or her gender or age, it can be a sign of hormonal imbalance and should be discussed with a doctor.
So, puberty doesn't actually cause the creation of hair follicles; it merely changes the hair that grows from these follicles. It is also interesting to note that according to researchers, humans have the same number of hair follicles as an ape. The only difference is the texture of the hairs that grow from these follicles.
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See also:
How to analyze hair
Hair and hormonal changes
How does a girl get rid of small hairs under her nose
Receding hair lines