You have about 5 million hairs on your body. A small portion of these is found on your head, maybe 100,000 — 150,000.
The protein that makes up your fingernails and skin, keratin is also what makes up your hair. The hair follicle is a sack that surrounds the hair root. The root is provided nourishment from surrounding blood vessels. Hair follicles develop while you are in your mother's womb — follicles are not formed after birth.
The hair is produced in the papilla at the base of the follicle. The papilla is nourished by blood flow and provides nutrients for the growing hair.
In both men and women, the male hormone androgen regulates hair growth. The growth of the hair on your head is not directly related to androgen levels, but is influenced by the amounts of DHT, dihydrotestosterone.