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Puberty is the time in life when a boy or girl becomes sexually mature. It is a process that usually happens between ages 10 and 14 for girls and ages 12 and 16 for boys. It causes physical changes, and affects boys and girls differently.

In girls:

• The first sign of puberty is usually breast development.
• Then hair grows in the pubic area and armpits.
• Menstruation (or a period) usually happens last.

In boys:

• Puberty usually begins with the testicles and penis getting bigger.
• Then hair grows in the pubic area and armpits.
• Muscles grow, the voice deepens, and facial hair develops as puberty continues.

Both boys and girls may get acne. They also usually have a growth spurt (a rapid increase in height) that lasts for about 2 or 3 years. This brings them closer to their adult height, which they reach after puberty.

NIH: National Institute of Child Health and Human Development