Puberty is a sequential series of physical changes that lead to sexual maturity. These changes are described by Tanner stages, named after British pediatrician Dr. James Tanner. The stages are based on the development of secondary sex characteristics. Tanner stage 1 is the prepubescent stage with no observable sexual development; stages 2 through 5 are the four stages of puberty.
Tanner Stage 2
For most girls, sexual development begins with breast buds, a small mound of breast tissue under the areola (the area of pigmented skin at the center of the breast). This typically begins at age 8 to 10. Notably, a girl's growth spurt in height generally begins roughly a year before breast development commences.
In boys, puberty begins with growth of the testicles at age 9.5 to 13 years. The skin of the scrotum becomes thinner and redder than in prepubescence. The growth spurt has not yet begun.
In both boys and girls, a few fine but dark pubic hairs become noticeable. Adult body odor begins for both sexes.
Tanner Stage 3
Female breast development continues to expand peripherally beyond the areola with more elevation. The areola also grows, but does not take on a separate shape. The peak rate of growth in height is underway during this stage. Vaginal discharge typically begins, and approximately 20 percent of girls will experience the onset of menstruation.
The hallmark of stage 3 for boys is lengthening of the penis. The testicles and scrotum also continue to grow. Ejaculation usually begins including nocturnal ejaculations, commonly known as wet dreams. Boys may become fertile during this stage of puberty. The growth spurt in height for boys generally begins during this stage.
Moderate amounts of course, darkly pigmented pubic hair are seen in the genital area of both girls and boys. It is typically limited to the midline in this stage of development.
Tanner Stage 4
Female breast and areola growth continues and a separate mound of tissue elevates the areola above the rest of the breast. Roughly 56 percent of adolescent girls experience the onset of menstruation during this stage. The peak rate of growth typically ends for females in this stage.
Among boys, the penis growths in length and circumference. The testicles and scrotum continue to grow, and the skin of the scrotum darkens. Sperm production is present. The male voice typically begins to deepen during this stage.
The pubic hair appears adult-like for both boys and girls, with the exception that it does not yet extend to the inner thigh.
Tanner Stage 5
The female breasts reach full adult size. The breast and areola follow the same contour, and the nipple now projects from the areola. The female genitalia reach their mature adult size and appearance.
The male genitalia also reach adult size and appearance. The growth spurt in height begins to slow. This is the stage when facial hair usually appears.
The pubic hair in both males and females becomes adult in appearance and distribution, including extension to the inner thigh. On average, the time from the onset to completion of puberty is roughly four years for females and three years for males.