Sometimes referred to as teenage years, youth, or puberty, adolescence is the transitional period between childhood and maturity, occurring roughly between the ages of 10 and 20.
The word adolescence is Latin in origin, derived from the verb adolescere, which means "to grow into adulthood." Adolescence is a time of moving from the immaturity of childhood into the maturity of adulthood. There is no single event or boundary line that denotes the end of childhood or the beginning of adolescence. Rather, experts think of the passage from childhood into and through adolescence as composed of a set of transitions that unfold gradually and that touch upon many aspects of the individual's behavior, development, and relationships. These transitions are biological, cognitive, social, and emotional.
The biological transition of adolescence, or puberty, is perhaps the most observable sign that adolescence has begun. Technically, puberty refers to the period during which an individual becomes capable of sexual reproduction. More broadly speaking, however, puberty is used as a collective term to refer to all the physical changes that occur in the growing girl or boy as the individual passes from childhood into adulthood.
The timing of physical maturation varies widely. In the United States, menarche (onset of menstruation) typically occurs around age 12, although some youngsters start puberty when they are only eight or nine, others when they are well into their teens. The duration of puberty also varies greatly: 18 months to six years in girls and two to five years in boys.
The physical changes of puberty are triggered by hormones, chemical substances in the body that act on specific organs and tissues. In boys a major change incurred during puberty is the increased production of testosterone, a male sex hormone, while girls experience increased production of the female hormone estrogen. In both sexes, a rise in growth hormone produces the adolescent growth spurt, the pronounced increase in height and weight that marks the first half of puberty.
Perhaps the most dramatic changes of puberty involve sexuality. Internally, through the development of primary sexual characteristics, adolescents become capable of sexual reproduction. Externally, as secondary sexual characteristics appear, girls and boys begin to look like mature women and men. In boys primary and secondary sexual characteristics usually emerge in a predictable order, with rapid growth of the testes and scrotum, accompanied by the appearance of pubic hair. About a year later, when the growth spurt begins, the penis also grows larger, and pubic hair becomes coarser, thicker, and darker. Later still comes the growth of facial and body hair, and a gradual lowering of the voice. Around mid-adolescence internal changes begin making a boy capable of producing and ejaculating sperm.
In girls, sexual characteristics develop in a less regular sequence. Usually, the first sign of puberty is a slight elevation of the breasts, but sometimes this is preceded by the appearance of pubic hair. Pubic hair changes from sparse and downy to denser and coarser. Concurrent with these changes is further breast development. In teenage girls, internal sexual changes include maturation of the uterus, vagina, and other parts of the reproductive system. Menarche, the first menstrual period, happens relatively late in puberty. Regular ovulation and the ability to carry a baby to full term usually follow menarche by several years.