Puberty is a sequence of events in which physical changes occur, resulting in adult physical characteristics and capacity to reproduce. These physical changes are regulated by changes in the levels of hormones that are produced by the pituitary gland—luteinizing hormone and follicle-stimulating hormone. At birth, levels of these hormones are high, but they decrease within a few months and remain low until puberty. Early in puberty, levels of luteinizing hormone and follicle-stimulating hormone increase, stimulating the production of sex hormones. The increased levels of sex hormones (primarily estrogen) result in physical changes, including maturation of the breasts, ovaries, uterus, and vagina. Normally, these changes occur sequentially during puberty, resulting in sexual maturity.
When puberty begins and how quickly its changes occur are influenced by many other factors, such as
Nutrition and general health: In the United States, puberty begins about 3 years earlier today than it did a century ago. The reasons probably include improvements in nutrition and general health.
Weight: Puberty tends to start earlier in girls who are slightly overweight and tends to start later in girls who are greatly underweight and malnourished.
Genetics: Puberty occurs earlier in girls whose mothers matured early.
Ethnic group: Puberty tends to start earlier in blacks and Hispanics than in Asians and whites who are not Hispanic.
The first change of puberty is usually the start of breast development (breast budding). In girls who live in the United States, this change usually occurs around age 8 to 13. Shortly afterward, pubic hair and underarm hair begin to grow.
The growth spurt accompanying puberty typically begins about when pubic hair and underarm hair begin to grow. Growth is fastest relatively early in puberty (before menstrual periods begin) and peaks at about age 12. Then growth slows considerably, usually stopping between the ages of 14 and 16.
The interval from breast budding to the first menstrual period (menarche) is usually about 2 to 3 years. In the United States, girls, on average, have their first period when they are almost 13, but there is a wide range (typically between ages 10 and 16 years), depending on many factors. Menstrual cycles are usually irregular at first and can take up to 5 years to become regular.
Also during puberty, the girl's body shape changes, and the percentage of body fat increases and accumulates in the hips and thighs.