Menstruation is a woman's monthly bleeding, also called a "period". When a woman menstruates, her body sheds the lining of the uterus (womb). The menstrual blood flows from the uterus through a small opening in the cervix and out of the body through the vagina.

In the United States, most girls start menstruating at age 12, but girls can start menstruating between the ages of 8 and 16. The first period usually 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.

What is the menstrual cycle?

A woman's periods come regularly due to a monthly rhythm of changes to the body. These monthly changes are called the menstrual cycle.

The menstrual cycle prepares a woman's body for pregnancy and creates hormones that are important for good health.

The menstrual cycle is counted from the first day of a 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.

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.

The rise and fall of female hormones, such as estrogen and progesterone, 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.

Menstruation is the shedding of this uterine blood and tissue.

What is a typical menstrual period like?

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.

How long does a woman have periods?

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.

What are the signs of menstruation?

Bleeding from the vagina is the primary sign of menstruation. Some women have other symptoms around the time of menstruation, including:

  • cramping, bloating, and sore breasts
  • food cravings
  • mood swings and irritability
  • headaches and fatigue

If these symptoms are severe, it might be a sign of premenstrual syndrome(PMS).  Premenstrual syndrome usually occurs one or two weeks before menstruation. PMS may affect a woman of any age who has menstrual periods. If the symptoms disrupt your lifestyle, you may want to seek medical care.

Are there treatments for painful menstruation?

Placing a heating pad on the abdomen and over-the-counter pain relievers may help lessen the symptoms. It is important to tell your health care provider if you have severe cramping and pain or other symptoms, during menstruation.

What kinds of problems do women have with their periods?

Women can have a range of problems with their periods, including pain, heavy bleeding, and skipped periods. Menstrual irregularities could be a sign that something is wrong. Menstrual irregularities can mean bleeding between your periods, skipping a period, or having very heavy menstrual periods. 

Types of problems include:

  • Amenorrhea. Amenorrhea is the lack of a menstrual period. This term is used to describe the absence of a period in young women who haven't started menstruating by age 15, or women who haven't had a period for 90 days, even if they haven't been menstruating for long.
  • Dysmenorrhea. Dysmenorrhea causes painful periods, including severe cramps.
  • Abnormal uterine bleeding. This is vaginal bleeding that’s different from normal menstrual periods. It includes bleeding between periods, after sex, spotting anytime in the menstrual cycle, bleeding heavier or more days than normal, or bleeding after menopause.

In both teens and women nearing menopause, hormonal changes can cause long periods along with irregular cycles. Even if the cause is hormonal changes, you may be able to get treatment. You should keep in mind that these changes can occur with other serious health problems, such as uterine fibroids, polyps, or even cancer. See your doctor if you have any abnormal bleeding.

When should a girl or woman see her doctor about her period?

  • See your doctor about your period if:
  • You have not started menstruating by the age of 15.
  • You have not started menstruating within 3 years after breast growth began, or if breasts haven't started to grow by age 13.
  • Your period suddenly stops for more than 90 days.
  • Your periods become very irregular after having had regular, monthly cycles.
  • Your period occurs more often than every 21 days or less often than every 35 days.
  • You are bleeding for more than 7 days.
  • You are bleeding more heavily than usual or using more than 1 pad or tampon every 1 to 2 hours.
  • You bleed between periods.
  • You have severe pain during your period.
  • You suddenly get a fever and feel sick after using tampons.

How often should I change my pad and/or tampon?

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). Toxic shock syndrome 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 toxic shock syndrome.

Reference: National Institutes of Child Health and Human Development

Last updated April 20, 2017

This information is for general educational uses only. It may not apply to you and your personal medical needs. This information should not be used in place of a visit, call, consultation with or the advice of your physician or health care professional.

Communicate promptly with your physician or other health care professional with any health-related questions or concerns.

Be sure to follow specific instructions given to you by your physician or health care professional.

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