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, followed by hair growth in the pubic area and armpits, and menstruation usually happens last. In boys, puberty usually begins with the testicles and penis getting bigger, followed by hair growth in the pubic area and armpits, muscle growth, deepening of the voice, and development of facial hair as puberty continues. Both boys and girls may experience acne and usually have a growth spurt that lasts for about 2 or 3 years, bringing them closer to their adult height, which they reach after puberty.