Puberty in Girls and Boys

Teenage bodies undergo dramatic changes, though the rate at which adolescents mature varies markedly from person to person. Many boys grow three to four inches in a year, for example, while some grow twice that amount. It is both realistic and reassuring to think of a range when assessing what is a "normal" indicator of a teenager’s development—from the onset of adult sexual characteristics to the sudden appearance of skin blemishes (acne).

The following milestones are based on averages and general recommendations and should be viewed as a guide rather than a rigid standard.

Changes in Girls

The onset of sexual maturation in girls usually begins about two years earlier than it does in boys. The process of puberty can take anywhere from two to six years and can begin anytime between ages 8 and 14. (If a girl begins developing before age 8, puberty is considered to be premature, and a doctor should be consulted.)

An increase in height usually begins at age 10 to 11 and continues to age 15 to 16. If a noticeable increase in height has not started by age 15, consult a physician.

Breast development usually begins at age 10 to 11, but it may start as early as 8 or may not occur until age 14 or 15. One breast may start to develop before the other. If noticeable breast development doesn’t begin by age 16, consult a physician.

The emergence of body hair usually begins in the pubic area about the same time as breast development, usually starting at age 10 or 11 but sometimes not occurring until age 13 or 14. Underarm and leg hair appears a year to two later. In general the color, thickness, and pattern of body hair is quite variable.

Menstrual periods usually begin between ages 11 and 14, about one year after breasts begin to develop, although periods may not occur until ages 15 to 17. If menstruation begins before age 10, or has not begun by age 17, or if periods are irregular, a physician should be consulted.

On average, a menstrual period occurs every 28 days and lasts 4 days, although periods occurring 23 to 35 days apart and lasting 2 to 7 days are still considered normal. Painful menstrual cramps, or dysmenorrhea, are unusual during the first year or two of menstruation but may occur in later adolescence.

During the first year or two after menarche (the first menstrual period), an adolescent girl may experience irregular periods, skipping one or many months between periods. It can take a while for the hypothalamus, the part of the brain that regulates reproduction, to coordinate the release of the various hormones that control the menstrual cycle. This is quite common and is not cause for concern. However, it is possible for pregnancy to occur any time after menarche, so sexually active teenage girls need birth control, and a missed period in a sexually active girl should not be ignored.

A certain amount of body fat appears to be necessary for menstruation to occur, and some young female athletes, such as gymnasts or ballet dancers, have so little body fat that menstruation is delayed. This is not harmful as long as menstruation begins by age 16. After that, a failure to menstruate can indicate a lower-than-normal level of estrogen, which can contribute to thinning and weakening of bones.

An increase in weight and body fat begins at ages 10 to 11, when female hormones trigger an increase in fat in the breasts, hips, thighs, and buttocks. Fat makes up about 25 percent of total body weight in girls, compared to 15 to 20 percent in boys.

If body weight does not increase, or if it increases and then drops, consult your physician, since this may be an indication of an eating disorder or another medical problem.

The development of sweat glands, which are responsible for increased perspiration, usually begins at age 12 to 13. These glands can cause underarm odor (which is not present in young children).

Changes in Boys

Growth in teenage boys occurs in spurts, generally over four to five years. The first growth spurt may start anytime between ages 10 and 14. Outside that age range, puberty is either delayed or premature. The following changes occur in a boy’s physical development.

An increase in height usually begins at age 12 or 13 and continues until age 17 or 18. (If some visible growth has not occurred by age 15, consult your doctor.)

Body hair appears, usually beginning in the pubic area at ages 11 to 12. Hair is first visible on skin around the base of the penis, then thickens and extends to the scrotum. Underarm hair subsequently develops at age 13 to 15, along with the first appearance of facial hair (which generally develops more slowly than other body hair). The color, pattern, and thickness of body hair varies considerably from person to person.

The testicles, penis, and scrotum enlarge, starting at about age 12 to 13. The skin of the scrotum and penis also darkens, and about a year after the penis begins to lengthen, most boys are able to ejaculate semen for the first time. Genital growth is usually completed by age 17.

The larynx, or voice box, begins to grow at age 13 or 14; approximately a year later the voice begins to deepen. (If the voice has not deepened by age 16, consult a physician.)

The development of sweat glands, which are responsible for increased perspiration, usually begins at ages 13 to 15. These glands can cause underarm odor (which is not present in younger children).

Publication Review By: the Editorial Staff at

Published: 22 Jun 2010

Last Modified: 06 Nov 2014