Sexual Development


Puberty and Adolescence

Puberty is the time in which a child's sexual and physical characteristics mature because of changes in their hormones. Adolescence is the period of a child’s development that begins with the onset of puberty and ends as the adolescent enters adulthood. It is generally considered to be the years from ages 12 to 18. Here’s a breakdown of the changes that occur during each of those stages, as well as some parenting advice, according to the National Institutes of Health.

The exact age a child enters puberty depends on a number of different factors, such as genes, nutrition and gender. During puberty, their bodies produce hormones that cause physical changes.

  • In girls, the ovaries begin to increase production of estrogen and other female hormones.
  • In boys, the testicles increase production of testosterone.

The adrenal glands produce hormones that cause increased armpit sweating, body odor, acne, and armpit and pubic hair. The child will often need an underarm deodorant or antiperspirant during this time.

Puberty in Girls

Breast development is the main sign that a girl is entering puberty. The first menstrual period usually follows within about two years. Before the first menstrual period, a girl will normally have:

  • An increase in height
  • An increase in hip size
  • Clear or whitish vaginal secretions
  • Pubic, armpit and leg hair growth

Menstrual cycles occur over about one month (28 to 32 days). At first, the menstrual periods may be irregular. A girl may go two months between periods, or may have two periods in one month. Over time, periods become more regular. Keeping track of when the period occurs and how long it lasts can help predict when the next menstrual period will occur.

During or just before each period, the girl may feel moody or emotional, and her body may feel puffy or swollen (bloated). Premenstrual syndrome may begin to develop, especially as the girl gets older.

In girls, puberty is usually finished by age 17. Any increases in height after this age are uncommon. Although a girl has reached full physical maturity at this time, her educational and emotional maturity continue to grow.

Girls Timeline:

  • Girls have a rapid growth in height between ages 9.5 and 14.5, peaking at around age 12.
  • Girls may begin to develop breast buds as early as 8 years old. Breasts develop fully between ages 12 and 18.
  • Pubic, armpit and leg hair usually begin to grow at about age 9 or 10, and reach adult patterns at about 13 or 14 years.
  • The beginning of menstrual periods typically occurs about two years after early breast and pubic hair appear. It may occur as early as age 10, or as late as age 15. The average age of menstruation in the United States is about 12.5 years.

Visit for advice and tips on taking with your teenaged girl. GirlsHealth.govalso offers answers to some questions your teen may have about their changing body.

For families of a child with a disability, specific Parent’s Guides on Puberty are available for girls. Visit to view these guides and toolkits.

Puberty in Boys

The first sign of puberty in boys is enlargement of both testicles. Afterward, boys will normally experience:

  • Faster growth, especially height
  • Hair growth under the arms, on the face and in the pubic area
  • Increased shoulder width
  • Growth of the penis, scrotum (with reddening and folding of the skin) and testes
  • Nighttime ejaculations (nocturnal emissions or “wet dreams”)
  • Voice changes

The testes constantly produce sperm. Some sperm can be stored in a structure called the epididymis. Sometimes the stored sperm are released as part of the normal process to make room for new sperm. This can occur automatically during sleep (nocturnal emissions), or following masturbation or sexual intercourse. Nocturnal emissions are a normal part of puberty.

Boys Timeline:

  • Boys may begin to notice that their testicles and scrotum grow as early as age 9. Soon, the penis begins to lengthen. By age 16 or 17, their genitals are usually at their adult size and shape.
  • Pubic hair growth—as well as armpit, leg, chest and facial hair—begins in boys at about age 12 and reaches adult patterns at about 15 or 16 years.
  • Boys do not start puberty with a sudden incident, like the beginning of menstrual periods in girls. Having regular nocturnal emissions (wet dreams) marks the beginning of puberty in boys. Wet dreams typically start between ages 13 and 17, with the average at about 14.5 years.
  • Boys’ voices change at the same time the penis grows. Nocturnal emissions occur with the peak of the height growth spurt.

For families of a child with a disability, specific Parent’s Guides on Puberty are available for boys. Visit to view these guides and toolkits.


Adolescence is the time between the onset of puberty and adulthood, generally between ages 12 and 18. The adolescent experiences not only physical growth and change, but also emotional, psychological, social and mental change and growth.

In mid- to late adolescence, young people often feel the need to establish their sexual identity by becoming comfortable with their body and sexual feelings. Through romantic friendships, dating and experimenting, adolescents learn to express and receive intimate or sexual advances. Young people who do not have the opportunity for such experiences may have more difficulty with intimate relationships when they are adults.