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Menstruation (men-STRAY-shuhn) is a woman's monthly bleeding. When you menstruate, your body sheds the lining of the uterus (womb). Menstrual blood flows from the uterus through the small opening in the cervix and passes out of the body through the vagina (see how the menstrual cycle works below). Most menstrual periods last from 3 to 5 days.
When periods (menstruations) come regularly, this is called the menstrual cycle. Having regular menstrual cycles is a sign that important parts of your body are working normally. The menstrual cycle provides important body chemicals, called hormones, to keep you healthy. It also prepares your body for pregnancy each month. A cycle is counted from the first day of 1 period to the first day of the next period. The average menstrual cycle is 28 days long. Cycles can range anywhere from 21 to 35 days in adults and from 21 to 45 days in young teens.
The rise and fall of levels of hormones during the month control the menstrual cycle.
In the first half of the cycle, levels of estrogen (the “female hormone”) start to rise. Estrogen plays an important role in keeping you healthy, especially by helping you to build strong bones and to help keep them strong as you get older. Estrogen also makes the lining of the uterus (womb) grow and thicken. This lining of the womb is a place that will nourish the embryo if a pregnancy occurs. At the same time the lining of the womb is growing, an egg, or ovum, in one of the ovaries starts to mature. At about day 14 of an average 28-day cycle, the egg leaves the ovary. This is called ovulation.
After the egg has left the ovary, it travels through the fallopian tube to the uterus. Hormone levels rise and help prepare the uterine lining for pregnancy. A woman is most likely to get pregnant during the 3 days before or on the day of ovulation. Keep in mind, women with cycles that are shorter or longer than average may ovulate before or after day 14.
A woman becomes pregnant if the egg is fertilized by a man’s sperm cell and attaches to the uterine wall. If the egg is not fertilized, it will break apart. Then, hormone levels drop, and the thickened lining of the uterus is shed during the menstrual period.
See how the menstrual cycle works below.
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During your period, you shed the thickened uterine lining and extra blood through the vagina. Your period may not be the same every month. It may also be different than other women's periods. Periods can be light, moderate, or heavy in terms of how much blood comes out of the vagina. This is called menstrual flow. The length of the period also varies. Most periods last from 3 to 5 days. But, anywhere from 2 to 7 days is normal.
For the first few years after menstruation begins, longer cycles are common. A woman's cycle tends to shorten and become more regular with age. Most of the time, periods will be in the range of 21 to 35 days apart.
Women can have a range of problems with their periods, including pain, heavy bleeding, and skipped periods.
Visit girlshealth.gov for information on getting your period.
In the United States, the average age for a girl to get her first period is 12. This does not mean that all girls start at the same age. A girl can start her period anytime between the ages of 8 and 15. Most of the time, the first period starts about 2 years after breasts first start to develop. If a girl has not had her first period by age 15, or if it has been more than 2 to 3 years since breast growth started, she should see a doctor.
Women usually have periods until menopause. Menopause occurs between the ages of 45 and 55, usually around age 50. Menopause means that a woman is no longer ovulating (producing eggs) or having periods and can no longer get pregnant. Like menstruation, menopause can vary from woman to woman and these changes may occur over several years.
The time when your body begins its move into menopause is called the menopausal transition. This can last anywhere from 2 to 8 years. Some women have early menopause because of surgery or other treatment, illness, or other reasons. If you don’t have a period for 90 days, you should see your doctor. He or she will check for pregnancy, early menopause, or other health problems that can cause periods to stop or become irregular.
See your doctor about your period if:
You should change a pad before it becomes soaked with blood. Each woman decides for herself what works best. You should change a tampon at least every 4 to 8 hours. Make sure to use the lowest absorbency tampon needed for your flow. For example, use junior or regular tampons on the lightest day of your period. Using a super absorbency tampon on your lightest days increases your risk for toxic shock syndrome (TSS). TSS is a rare but sometimes deadly disease. TSS is caused by bacteria that can produce toxins. If your body can’t fight the toxins, your immune (body defense) system reacts and causes the symptoms of TSS (see below).
Young women may be more likely to get TSS. Using any kind of tampon puts you at greater risk for TSS than using pads. The Food and Drug Administration (FDA) recommends the following tips to help avoid tampon problems:
If you have any of these symptoms of TSS while using tampons, take the tampon out, and contact your doctor right away:
For more information about menstruation and the menstrual cycle, call womenshealth.gov at 800-994-9662 (TDD: 888-220-5446) or contact the following organizations:
Menstruation and the menstrual cycle fact sheet was reviewed by:
Lawrence M. Nelson, M.D.
National Institute of Child Health & Human Development
National Institutes of Health
Content last updated: December 23, 2014