Merck Manual

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Puberty in Boys


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Last full review/revision Jun 2020| Content last modified Jun 2020
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What is puberty?

Puberty is the period of growth and development in which children and adolescents of both sexes begin to develop adult physical features, such as breasts or facial hair, and become able to reproduce (create babies). For boys, puberty usually happens between ages 10 and 14, though it can happen earlier or later.

What causes puberty in boys?

The entire reproductive system, including puberty, is controlled by hormones. Hormones are chemical messengers made in certain parts of your body that travel through the blood to signal other parts of the body what to do.

Puberty in boys starts when hormones released by the brain cause the testicles to develop. The testicles then release the hormone testosterone. Testosterone is a male sex hormone that causes people to develop facial hair, a deeper voice, and other male physical features. Hormones also cause the testicles to make sperm.

What changes happen during puberty in boys?

The following physical change take place, usually in this order:

  • First, the scrotum (skin around the testicles) and testicles get larger

  • Soon after, the penis grows longer—this usually happens between ages 11½ and 13

  • The seminal vesicles and prostate, which are involved in making semen, grow larger

  • Pubic hair grows

  • A growth spurt happens, and a boy develops bigger muscles and broader shoulders

  • Hair grows on the face and under the arms

  • Ejaculation (the release of sperm from the penis) usually becomes possible around age 12 ½ to 14 years

  • Fertility (ability to father children) happens as an older teen

Some boys’ breasts grow (gynecomastia) during early puberty, but this usually goes away within a year.

What can go wrong with puberty?

Problems with puberty usually involve hormones. There are many different hormone problems that result in too few hormones so that: 

  • Puberty is delayed or doesn't start at all

Less often, there are too many hormones and the boy has:

  • Early puberty

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