Puberty is the time when your body begins to change from a girl's body to a woman's body. It can take several years, and usually happens between the ages of nine and 17. Girls often start puberty before boys do.

Puberty happens when your brain and your sex organs send messages to the rest of your body. These messages are carried by chemicals called hormones. Hormones prepare your body and mind for sexual maturity (or adulthood).

Changes on the Outside

During puberty, girls' hips start to widen. You may not even notice this because it's a very subtle change. Next, coarse hair starts to grow under your arms and around your genitals, and finer hair begins to show on your legs and arms. Your breasts will start to change in size and shape. This change may happen fast or slow, depending on who you are.

You will probably begin to sweat more under your arms, and your sweat may smell different. This is easy to deal with — you can shower or bathe more often and begin using deodorant or antiperspirant if you don't like the smell.

During puberty, both girls and boys may develop acne (also called "pimples" or "zits"). Acne is very common and fairly easy to treat. Your health care provider can help you find a treatment that's right for you.

Sometimes the hormones of puberty can cause changes in your mood, making you feel more upset or excited about things than you used to. This is normal and it's a good idea to share your feelings with someone you trust, especially if you feel very sad or frustrated. Everyone goes through puberty, so you should be able to find an adult who understands to help you sort out your feelings.

Changes on the Inside

Hormones cause changes in your internal reproductive organs to get them ready to go through menstrual cycles and someday, perhaps, to have a child. At some point during puberty, you will start to have menstrual cycles and you will begin to get your monthly period. Most girls start having periods around the same age that their moms did, so you might want to ask your mom how old she was when she started. This is a good way to start talking to your mom about puberty.

Your first menstrual cycle starts inside where you can't see it, when an egg is released from your ovary. This is called ovulation. The ovaries usually release only one egg a month. The egg travels down the fallopian tube on its way to the uterus. It's hard to tell when this all happens, but it's usually about two weeks before you get your period.

In the meantime, the uterus has prepared itself by growing a thick inner lining of blood. This lining will be very important if you become pregnant. When a sperm fertilizes an egg, the fertilized eggs implants itself into the lining of the uterus, and pregnancy begins. When a woman isn't pregnant, this lining starts to break apart after a few days and it leaves the body through the vagina as menstrual flow. This bleeding usually lasts from three days to about a week and is called your "period."

Your Period

Periods are part of a monthly cycle that most healthy women's bodies go through during their reproductive years. You don't usually see or feel the rest of the cycle, so your period is an indicator that the cycle happened.

The menstrual flow is usually heaviest during the first few days. Some women get cramps before or during their periods. This is normal and usually goes away with Tylenol or ibuprofen or the use of a heating pad. If you have a lot of cramping, you can get help from your health care provider. Some women feel irritable, bloated, or have any number of other symptoms before their period starts. These symptoms are temporary and are called "PMS," which stands for premenstrual syndrome.

At first, most women have "irregular" periods, meaning they don't have them every month, or at the same time from month to month. Most women become more regular after a year, although some women never do. Most women's cycles are between 21 and 35 days long. There are a few things that could make your period late:

  • pregnancy

  • stress

  • excessive exercise or very low body fat — Many female athletes have irregular periods.

  • big changes in your life — taking a trip somewhere, moving

  • birth control — Some hormonal methods of birth control can affect a woman's menstrual cycle.

  • illness — Sometimes being sick or not feeling well can cause your period to be late.

Puberty is something everyone goes through, and it can be a very uncomfortable, awkward, and lonely time. But it is a good time to learn about your body and how it works. It is also a good time to start talking to your parents about their experiences when they were your age. You can also talk with a health care provider if you have questions that you don't want to ask your parents. Staff at the nearest Planned Parenthood health center can be very helpful.