Sexual Development of Boys

A boy goes through five stages of development during puberty.

Boys usually start to show the physical changes of puberty between the ages of 11 and 14, which is slightly older than when girls start puberty. The male sex hormone called testosterone and other hormones cause the physical changes.

Here are the five stages and what happens:

Stage 1: May begin as early as age 9 and continue until 14.

No sign of physical development but hormone production is beginning.

Stage 2: May begin anywhere from ages 11 to 13.

Height and weight increase rapidly.
Testicles become larger and scrotum hangs lower.
Scrotum becomes darker in color.
Fine hair growth begins at the base of the penis.
Hair growth may begin on the legs and underarms.

Stage 3: May begin anywhere from ages 12 to 14.

The penis, scrotum, and testicles grow.
Pubic hair becomes darker, thicker, and curlier.
Muscles become larger and shoulders become broader.
Sweat and oil glands become more active, which can result in acne.
Sperm production may begin.
Temporary swelling and tenderness may occur around nipples.
Height and weight continue to increase.
Hair growth on the legs and underarms continues.

Stage 4: May begin anywhere from ages 13 to 16.

Sperm production has usually begun.
The larynx (Adam's apple) increases in size. Vocal chords become longer and thicker, and the voice begins to break or crack, then becomes low.
Height and weight continue to increase.
Penis and testicles continue to grow.
Pubic hair increases in amount and becomes darker, coarser, and curly.

Stage 5: May begin anywhere from ages 14 to 18.

Growth of facial hair begins.
Chest hair growth may begin (not all males get much chest hair).
Adult height is reached.
Penis and testicles have reached full adult size.
Pubic, underarm, and leg hair are adult color, texture, and distribution.
Overall look is that of a young adult man.

To learn more about boys and reproduction, check out Male Reproductive System.

Last revised: April 21, 2008