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Biological and physical changes in teens

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This fact sheet is part of the Teen talk: a survival guide for parents of teenagers series.

Adolescents are experiencing rapid changes in their bodies. During the teen years, they develop more adult-like physical features and might grow to double their height and weight. They are also becoming sexually mature, which involves more than physical changes. They are also developing new feelings about their bodies, sexuality, and intimate relationships.

Physical changes

Puberty occurs at widely varying ages. For girls, puberty can begin as early as 8 years of age but more commonly starts about age 10. Girls may experience a growth spurt in height and overall body shape in the early teen years. Girls will continue to grow, although a little more slowly, until age 17 or 18. They will begin to develop breast buds as early as 8 years of age, reaching full breast development anywhere from 12 to 18 years. Pubic hair growth as well as armpit and leg hair can begin at around age 9 or 10. Menarche, the beginning of menstrual periods, usually begins about two years following the first signs of puberty. That may be as early as age 10 and as late as age 15, with the average in the U.S. at about age 12.5.

Boys begin their growth spurt in height at age 10 or 11, peaking at around age 14. They finish growing physically at about age 21. The genitals begin to enlarge as early as 9 years of age, with adult size and shape achieved at about age 16 or 17. Boys' voices change at about the same time.

Early or late development

Early and late maturation has different implications for girls and for boys. With girls already ahead of their male peers, girls who begin maturing early may be out of sync with both male and female peers. Physical maturation can occur before maturing mentally, socially, and emotionally. Girls' concerns might include:

  • Looking different than classmates.

  • Being treated differently because of an "older" appearance.

  • Being the object of attention from older boys.

  • Lacking skills to cope with that attention.

This can result in having to deal with situations beyond their emotional and cognitive abilities.

For boys, concerns may be more about delayed development. As noted, most boys are already behind physically compared with their female classmates. If there is delayed development, the differences become more apparent. Teasing or bullying can occur resulting in low self-esteem or even depression.

What parents can do

Getting used to a rapidly changing body can lead teens to feel uncomfortable with their new shape and looks. They might also experience physical awkwardness when one part of the body hasn't caught up with the rest. Here’s what you as a parent can do to help your teen through this challenging phase of life:

  • Start talking about upcoming biological and physical changes at ages 8 or 9. Some children will become curious earlier and have questions.

  • Tailor discussions about biological and physical changes to your teen's age. Hold periodic conversations that build on previous talks.

  • Take your teen's concerns seriously. Listen closely and don't discount his feelings of being different or "something is wrong with me."

  • Avoid comments that will further embarrass your teen. For example, don't point out something about her physical appearance. Encourage other family members and adult friends to do the same.

  • Don't mistake physical maturity for overall maturity. It can take time for emotional maturity to catch up to a teen's body.

Related resources

The Teen Years ExplainedClea McNeely, PhD and Jayne Blanchard — This e-book can help both teens and adults to understand developmental changes and tips for how to apply this knowledge to your everyday life.

Colleen Gengler, Extension educator emerita in family relations

Reviewed by Jodi Dworkin, Extension specialist and associate professor in Family Social Science

Reviewed in 2018

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