Your body is changing; your moods may be unpredictable and sometimes even unexplainable. Don't worry. These changes during your teen years are normal.

Girls go through countless changes during the teenage years. And while changes in girls are different than those experienced by boys, all of these changes are a natural part of your development into an adult. These changes are called puberty.

How Your Body Changes During Puberty

Puberty lasts for several years and marks the life stage when your body is changing from a child to adult. The hormones — chemicals in your body — produce physical changes and emotional moments that seem uncontrollable. These changes are common during puberty and they happen to everyone. Though it may seem an alien creature is making your body change, don't worry, you're still you, just the "growing up" version.

Girls, one of the first changes you will notice is your breasts growing, usually between the ages of eight and 12. One breast might grow larger than the other; but don't worry. Most of the time your breasts will even out before they are finished developing. Just like your ears, they aren't always a perfect match. Once your breasts start growing, you will most likely want to buy a bra.

Another change you will notice is hair growth. Hair will grow under your arms, on your legs and on your pubic area. Shaving your underarms and legs is a personal choice. Some women do, others don't. It's your choice. If you decide to shave, make sure you use your own razor. Don't share razors with friends. And use either shaving cream or soap and water as a lubricant for shaving. If you want to shave, you should check with your parents first.

A less noticeable change is the widening of your hips and the slimming of your waist. Your stomach, bottom and legs might get larger too. All of these changes are making you look more like a woman than a girl, and they are all normal, expected changes.

Another sign of puberty could be all over your face. It's called acne, pimples, zits... This aggravating condition may be mild (blackheads and whiteheads), moderate (larger inflamed-looking blemishes) or severe (large cysts or nodules). Greasy foods and dirt do not cause acne; acne is caused by a build-up of oil, microorganisms and dead skin cells in the hair follicles under the skin. When whiteheads rupture, the "acne cascade" is triggered and surrounding tissue is affected. Keeping your face clean is one way to combat acne. Also, don't squeeze pimples. This can make them much worse and increase the chance of scarring. Often the condition of your skin during puberty will be similar to what your parents experienced when they were teenagers. If your acne concerns you, talk to your parents and/or a health care professional. Acne can be treated.