What are the physical stages of puberty in girls and boys?
The changes that happen during the process of puberty have a typical pattern in both boys and girls, with a generally predictable sequence of events. In most girls, the first sign of puberty is the beginning of breast development (breast buds), which occurs at an average age of approximately 11 years. In girls, the growth of pubic hair typically begins next, followed by the growth of hair in the armpits. A minority of girls, however, begin to develop pubic hair prior to breast development. The onset of menstruation (having periods) usually happens later than the other physical changes and usually occurs around two and a half years after the onset of puberty.
A regular pattern of ovulation, corresponding to achievement of fertility, usually develops rapidly once a girl begins having menstrual periods. However, girls who have a later onset of menstruation (after age 13) tend to have lower rates of regular ovulation in the years following the onset of menstruation. Studies have shown that one-half of adolescent girls who first begin to menstruate after age 13 will not ovulate regularly over the next four and a half years.
In boys, an increase in the size of the testicles is the first change observed at the onset of puberty. Enlargement of the testicles begins at an approximate average age of 11 and a half years in boys and lasts for about six months. After enlargement of the testicles, the penis also increases in size. Enlargement of the testicles and penis almost always occurs before the development of pubic hair. The next stage is the growth of pubic hair and hair in the armpits. Next, the voice becomes deeper and muscles increase in size. The last step is usually the development of facial hair.
Fertility is achieved in males near the onset of puberty, when a surge in testosterone triggers the production of sperm.
The sequence of changes in puberty has been characterized by physicians and is referred to as sexual maturity rating (SMR) or Tanner stages, named after a physician who published a description of the sequence of physical changes in puberty in 1969. Tanner stages are determined by the development of the secondary sex characteristics and encompass changes in the size and appearance of the external genitalia, the development of pubic hair, and breast development in girls. Tanner stages allow doctors to classify the extent of development of sex characteristics into five distinct steps ranging from stage 1 (prepubertal) to stage 5 (mature adult type).