The female body goes through five basic stages of sexual development during the progression from childhood to adulthood. Doctors generally use the Tanner scale to measure an individual child's progress through these stages, based on her development of primary and secondary sex characteristics. This scale is named after James Tanner, the British paediatrician who invented it.
Prepubescence (Tanner Stage 1)
In this stage, a girl should have no hairs in her pubic region, although the fine "peach fuzz" that covers the body may be present. There should be no glandular tissue in the breasts, and the areolae should conform to the general chest line. Girls may undergo an increase in height growth velocity around the age of 9, though this varies from child to child.
Early Puberty (Tanner Stage 2)
Peak height velocity for girls occurs at 11.5 years, on average. During this time, breast tissue should begin to bud, and the areolae should start to enlarge. There should only be a minimal amount of pubic hair growth, with the main growth taking place on the labia. This hair should be pigmented and somewhat coarse. African-American females tend to experience this stage a year earlier than white females of the same age.
Mid-Puberty (Tanner Stage 3)
When a girl is in the throes of puberty, her breasts typically grow larger and she experiences several growth spurts. The areolae should get larger as the breast tissue increases. Pubic hair becomes darker and coarser, and begins to spread laterally. At this time, girls may also start to experience acne (i.e., pimples, whiteheads and blackheads), and develop axillary, or armpit, hair.
Late Puberty (Tanner Stage 4)
In this stage, a girl may become uncomfortable with her pubertal weight gain, which accounts for 50 per cent of her ideal adult body weight. Breast tissue should become larger and gain elevation. Each areola should grow into a second, smaller mound that projects from the breast contour. Pubic hair should reach its adult quantity, but should not spread to the junction of the thigh. A girl may wish to wear a bra at this stage, depending on the amount of breast tissue she has developed.
After Puberty (Tanner Stage 5)
In this final stage, breast tissue reaches adult size, and the areolae shrink back to the general contour of the breasts. Breast tissue will generally stay this size, unless the female gains weight and thus produces more oestrogen. Pubic hair should be dark and coarse, and spread to the medial thigh. Approximately 90 per cent of females may experience sparse pubic hair growth that extends to the belly button.