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for their health by adopting a healthy lifestyle. Along with disorders that can occur at any age, some health problems are common in adolescents. For example, acne (see page 1065) is a chronic skin disorder affecting the face and back that almost always begins at puberty. Sports injuries (see page 978) are common among teenagers. Headaches, particularly migraines (see page 684), may appear for the first time during adolescence. Infectious mononucleosis (see page 935) is a viral infection that often develops during the teen years. Some forms of cancer—such as Hodgkin’s disease (see page 626) or leukemia (see page 621)—often first appear in adolescents and young adults.

Stages of Puberty in Girls and Boys

Stages of Puberty in Girls

Puberty starts in the brain when the hypothalamus stimulates the pituitary gland to signal the ovaries to produce hormones. These hormones stimulate the ovaries to produce estrogen. Girls have a significant growth spurt starting at about age 10, brought on by sex hormones such as estrogen. Because of estrogen, girls have a higher ratio of fat to muscle and bone than boys do. Girls grow and develop earlier than boys and are usually taller and bigger than boys of the same age. By age 18, girls have usually reached their full adult height and often weigh nearly double what they weighed when puberty began.

Prepuberty

In the period immediately preceding puberty, there are no visible signs of sexual development, but the ovaries are getting ready to produce female sex hormones.

Early puberty

The first outward signs of puberty appear. Girls have a slight increase in the size of their breasts and, sometimes, more prominent nipples caused by the growth of breast tissue beneath. Girls start to grow quickly at this stage, not only getting taller but also rapidly putting on weight. Pubic hair grows in sparsely.

Middle puberty

Breasts become slightly larger, and pubic hair starts to fill in. Underarm hair and an increase in perspiration under the arms occur about a year or two after the appearance of pubic hair. Skin, particularly on the face, becomes more oily, possibly causing acne.

Late puberty

Girls grow taller and their weight increases. The breasts become fuller and nipples more prominent. Pubic hair is almost completely grown in. A white discharge from the vagina will appear from 6 to 12 months before a girl’s first menstrual period. Ovulation (the development and release of an egg from an ovary) may begin at about this time but usually does not become regular for a few years. Even with irregular periods and infrequent ovulation, it is possible to become pregnant at this time.

Maturity

Girls reach their full physical and sexual maturity at an average age of about 18. They reach their full adult height, and their breasts reach their adult size. Ovulation and menstrual periods usually become regular.

Prepuberty

Early puberty

Middle puberty

Late puberty

Maturity

Stages of Puberty in Boys

In boys, puberty starts when the hypothalamus produces sex hormones that are then excreted by the pituitary gland in the brain. These hormones act on the testicles to increase the secretion of the male sex hormone testosterone and other sex hormones. Testosterone increases muscle and bone mass. Boys may be temporarily shorter and smaller than girls of the same age but usually will be taller and heavier than most girls their age by the time they are 21.

Prepuberty

No signs of sexual development are visible before puberty, but the testicles are preparing to release sex hormones.

Early puberty

During this stage, the first signs of puberty appear. Boys will notice an enlargement of their testicles and scrotum.

Middle puberty

Pubic hair begins to grow during this stage. The penis grows longer, and boys may be able to ejaculate. Perspiration increases, and underarm hair may start to grow. The testicles continue to grow. Skin is oily, possibly causing acne. Because the vocal cords are starting to grow, the voice may crack or change pitch.