Most girls start to go through puberty sometime between the ages of 9 and 13. Puberty is the process that changes the body from that of a child to that of an adult. Boys and girls both go through puberty.

On the outside of the body, “breast budding” is usually the first sign that girls have entered puberty. It can be scary and exciting all at the same time. Girls notice slight changes in the size and shape of their breasts as they begin to grow. Girls might also notice acne, body odor, sweat and hair growing in the armpits and around the vulva. Hair on the legs will become more coarse and dark. Girls may also grow wider hips and larger breasts, although the size and shape of both of these body parts will be different on different girls. All of these changes are the result of hormones—chemicals in the body.

Mood swings can also be a part of puberty. A girl might feel happy one second, sad and angry the next—without being sure why she’s feeling that way. This can seem like a roller coaster ride because it feels like you have no control. The good news is that these mood swings are part of the process, and both boys and girls go through them. If you know what to expect, sometimes it’s easier to deal with them when they happen.
Inside a girl’s body, her uterus, cervix and ovaries are growing and maturing too. Sometime in the middle of puberty, girls usually get their first menstrual period. While many adult women have a period every 28 days, girls going through puberty may have irregular periods during the first few years of their menstrual cycles. Some will always have irregular periods.