Adolescence is the developmental stage between childhood and adulthood; generally refers to a period ranging from 12 or 13 years up to 19 or 21 years. Although its onset is often balanced with the onset of puberty, adolescence is characterized by psychological and social phases as well as biological changes. Adolescence can be prolonged, brief, or virtually nonexistent, depending on the type of culture in which it occurs. In simple societies, for example, the transition from childhood to adulthood tends to occur rather quickly and is marked by traditionally prescribed rites of passage. To counter this, in American and European societies, the transition period for young people has steadily lengthened over the last 100 years, giving rise to an adolescent subculture. As a result of this prolonged transition phase, a number of problems and concerns specifically associated with this age group have developed. Psychologists identify four areas that particularly affect the behavior and development of adolescents: physiological change and growth; cognitive or mental development; identity or personality formation; and parent-adolescent relationships. Physiological change: Between the ages of 9 and 15, almost all young people undergo a rapid series of physiological changes, known as the adolescent growth spurt. These hormonal changes include an acceleration of the body's growth rate; the development of pubic hair; the appearance of underarm or armpit hair about two years later. Changes occur in the structure and functioning of the reproductive organs; the mammary glands in girls; and the development of sweat glands, which often leads to an acne outbreak. In both sexes, these physiological changes occur at different times. This period of change can be very stressful for a preteen. Because at this stage of life appearance is very important. A teenager who develops very early or extremely late may experience a lot of ridicule from his peers. However, the time when a girl goes through this phase and a boy is different. Girls typically begin their growth spurt shortly after the age of 10. They tend to reach their peak around age 12 and tend to end by age 14. occurs almost two years later in boys. Therefore boys go through a difficult period where girls are taller and heavier than them. This awkward period occurs from ages ten and a half to thirteen. Timing is not the only difference in the pubertal period between boys and girls. In girls, breast enlargement is usually the first physical symptom