The Human Body


Puberty marks the second stage of physical sexual differentiation—the time when both primary and secondary sexual characteristics as well as adult reproductive capacity develop, and when sexual interest surges. Puberty typically begins in girls from 8 to 12 years of age, whereas boys start about two years later. The hypothalamus initiates pubertal changes by directing pituitary growth hormones and gonadotropins (hormones that control the ovaries and testes).

A girl's breasts grow, her pubic hair develops, and her body grows and takes on the rounded contours of an adult woman. This is followed by the first menstrual period (menarche) at about age 12 or 13 (although ages of onset range from 10 to 16.5), underarm-hair growth, and increased secretions from oil- and sweat-producing glands. It may take a year or two before menstruation and ovulation occur regularly. The hormones primarily responsible for these changes in young girls are the adrenal androgens, estrogens, progesterone, and growth hormone.

During puberty, a boy's testes and scrotal sac grow, his pubic hair develops, his body grows and develops, his penis grows, his voice deepens, facial and underarm hair appear, and secretions from his oil- and sweat-producing glands increase. Penile erections increase in frequency, and first ejaculation (thorarche) typically occurs sometime from the age of 11 to the age of 15. For a boy who has not masturbated, a nocturnal emission, or so-called wet dream, may be his first ejaculation. The ability to produce sperm may take another year or two and typically begins at about age 14. Growth hormone and androgens, particularly testosterone, are responsible for these pubertal changes in boys.

The fact that boys tend to develop more slowly than girls can cause some social awkwardness. Girls who have grown earlier may find themselves much taller than their dates, for example, and they may be more physically and psychologically mature than their male peers.

The first menstruation and first ejaculation are often considered the most important events of puberty, particularly for the individual. However, it is the development of the secondary sexual characteristics that serve as more apparent signals to others that the person is becoming a man or a woman. These signals lead to increasingly differential treatment of adolescent girls and boys by parents or other adults. The changes in hormone levels that occur during puberty may cause boys and girls to perceive the world in different ways, leading them to react differently to situations. Thus, puberty augments behavioral sex differences between young men and women. In some cultures and religions, puberty is recognized with rituals that mark the transition into adulthood.