Understanding Your Period and Menstrual Cycle

Reviewed by Brunilda Nazario, MD on August 08, 2011
From the WebMD Archives

Getting your period is a rite of passage surrounded by whispered rumor and mystery. Some girls dread it. Others can't wait. But all girls menstruate, and it helps to understand what's going on. Here are answers to seven common questions about a girl's period.

Why Do You Have a Period?

During the month, blood builds up in the lining of your uterus, which will help a baby develop when you're older and want to have a family. It's a natural process, says Sharon Horesh Bergquist, MD, at the Emory School of Medicine in Atlanta.

Most of the time, a fertilized egg is not implanted in your uterus, and the blood sheds out of your body during your monthly period.

What's Really Going On?

All kinds of changes occur in your body during your menstrual cycle. “The thing that makes it all happen is hormones,” says Atlanta pediatrician Deborah Pollack, MD. “You get hormone surges at night, with higher and higher and higher peaks, until your period begins.”


Raised levels of hormones helps eggs grow in your ovaries. Each month, one egg is released into your Fallopian tubes. This is called ovulation. The egg travels down the tube to your womb. And while this happens, your uterine lining thickens with blood -- just in case an egg is fertilized by sperm.

If the timing is right, the egg and sperm join together, and the fertilized egg attaches to the lining of your uterus. Pregnancy begins. Without a fertilized egg, the thickened lining has no purpose. So it sheds and comes out through your vagina. Your period has arrived.

When Will You Get Your Period?

The average age to start your period is 12, but many girls start younger, and others start later. "When you first start to get breasts and some pubic hair, you can usually jump forward two years and guess that’s when you’ll start, says Pollack.

“It might take up to two years for your period to get regular because the hormone surges are uneven,” Pollack says. At first, it's common to have one period, and then not another for a few months. But even if you don't have a period every month, you can still get pregnant.

Many girls start their periods around the same age as their mothers did. So ask your mother when she started her period, and how it felt. If you haven't started your period by age 16, you should talk to your doctor.

How Long Will Your Period Last?

“Every woman’s menstrual cycle is a little different,” says Bergquist. “But the typical menstrual cycle lasts three to five days, although a few days shorter or longer can still be normal."

Will You Get Cramps With Your Period?

Cramps can happen when your uterus contracts to help the shedded uterine lining move out of your body. Not all girls have cramps, but if you do, Bergquist says it helps to take anti-inflammatory pain relievers like ibuprofen (Advil, Motrin, Nuprin) or naproxen (Aleve, Feminax, Midol). You can buy them at any drugstore or supermarket. It also helps to place a heating pad on the area that hurts, she says.

If you have bad cramps that don't get better with the pain relievers and heating pad, talk to your doctor. Doctors can prescribe stronger or different medicines that help ease cramps.

Will Your Period Affect Your Emotions?

You may have heard that girls and women can get grouchy, weepy, and generally moody around the time of their periods. This is called PMS, and it's caused by the same hormones that bring on menstruation. Some girls do feel emotional changes around the time of their periods, but others don't.


“PMS can take on a variety of primarily psychological symptoms, such as mood irritability and unhappiness, as well as physical symptoms, such as bloating, breast tenderness, or constipation,” says Bergquist. 

If you have PMS, Bergquist says it's important to get adequate sleep, avoid caffeine, and try to eat low-sodium foods. Salt can make you bloat more. If a healthy lifestyle doesn't help, talk to your doctor about medicines that can help ease PMS symptoms.

Are You Prepared?

It’s a good idea to have a couple of tampons and sanitary pads stashed in your locker or book bag in case your period starts when you don't expect it. Bergquist also encourages girls to carry anti-inflammatory pain medicine for cramps, and even a change of panties in case of an accident.

Once you’ve had your period for a while, you’ll see there's nothing mysterious or embarrassing about it. It's part of the natural wonder of how a woman's body works.

WebMD Feature



Sharon Horesh Bergquist, MD, assistant professor of General Internal Medicine at Emory School of Medicine, Atlanta.

Deborah Pollack, M D, FAAP, Atlanta.

NIH web site, “Menstruation and the Menstrual Cycle.”

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