In males, these include the appearance of facial and other body hair, including in the pubic area and in the armpits, as well as the deepening of the voice tone. In females, hair develops in the pubic area and in the armpits, and the hips begin to broaden. For both sexes this is also a period of rapid development of the sweat glands. Generally, these changes prepare the body for sexual reproduction, but they also have important social and emotional aspects. Among boys, puberty tends to begin at about age 13, but may not start until 16 years of age.
Puberty tends to begin earlier in females, often two years earlier than boys.
However, the commencement of puberty varies among girls no less than among boys, and may not begin until age 14 or 15. Heredity can influence the onset of puberty, as can psychological and physical health. This may be due to anxiety about being different from one's peers and accompanying social pressure for conformity common during the adolescent years. Conversely, some youths undergo a peculiarly early pubescent transition, a condition called pubertus praecox. The functioning of the anterior pituitary, adrenals, or the gonads causes this condition.