Your Period and the Menstrual Cycle

Menstruation is vaginal bleeding that occurs each month. It is also known as menses, your menstrual period, or just your period.

Menstrual blood is made up of both blood and tissue that sheds each month from the lining of the uterus. It flows from the uterus through the small opening in the cervix and passes out of the body through the vagina.

Most periods last from three to five days.

Tampon and Calendar
Carol Yepes / Getty Images

What Is the Menstrual Cycle?

Menstruation is part of the menstrual cycle and helps the body prepare for the possibility of pregnancy. The first day of the cycle is the first day that bleeding occurs. The average menstrual cycle is 28 days long. However, a cycle can range anywhere from 23 days to 35 days.

Hormones in the body rise and fall during your cycle. Among those hormones are estrogen and progesterone, made in the ovaries, in addition to the follicle-stimulating hormone, or luteinizing hormone, made by the pituitary gland.

What Happens During the Menstrual Cycle?

In the first half of the menstrual cycle, your levels of estrogen rise and make the lining of the uterus grow and thicken. In response to the follicle-stimulating hormone, an egg (ovum) in one of the ovaries starts to mature. At about day 14 of your cycle, in response to a surge of luteinizing hormone, the egg leaves the ovary. This is called ovulation.

In the second half of the menstrual cycle, the egg begins to travel through the fallopian tube to the uterus. Progesterone levels rise and help prepare the uterine lining for pregnancy. If the egg becomes fertilized by a sperm cell and attaches itself to the uterine wall, you become pregnant. If the egg is not fertilized, it either dissolves or is absorbed into the body. If pregnancy does not occur, estrogen and progesterone levels drop and the thickened lining of the uterus is shed during the menstrual period.

During your menstrual period, the thickened uterine lining and extra blood are shed through the vaginal canal. A woman's period may not be the same every month, and it may not be the same as other women's periods. Periods can be light, moderate, or heavy, and the length of the period also varies. While most menstrual periods last from three to five days, anywhere from two to seven days is considered normal.

For the first few years after menstruation begins, periods may be very irregular. They may also become irregular in women approaching menopause. Sometimes birth control pills are prescribed to help with irregular periods.

Sanitary pads or tampons, which are made of cotton or other absorbent materials, are worn to absorb the blood flow. Sanitary pads can be placed inside your underpants, or you can insert a tampon into your vagina.

Women can have various kinds of problems with their periods, including pain, heavy bleeding, and skipped periods. The possible causes are varied:


This term is used to describe the absence of a period by the age of 16, or the absence of a period in women who used to have a regular period. Causes of amenorrhea include pregnancy, breastfeeding, and extreme weight loss caused by serious illness, eating disorders, excessive exercising, or stress. Hormonal problems (involving the pituitary, thyroid, ovary, or adrenal glands) or problems with the reproductive organs may be involved.


This manifests as pain during menstruation, including severe menstrual cramps. A hormone called prostaglandin is responsible for the symptoms. Some pain medicines available over the counter, such as ibuprofen, can help with these symptoms. Sometimes a disease or condition, such as uterine fibroids or endometriosis, causes the pain. 

Abnormal Uterine Bleeding

How do you know your bleeding is abnormal? Look out for extremely heavy bleeding, unusually long periods (also called menorrhagia), periods that come too close together, and bleeding between periods. In adolescents and women approaching menopause, hormonal imbalances often cause menorrhagia and irregular cycles. Sometimes this is called dysfunctional uterine bleeding (DUB). Other causes of abnormal bleeding include uterine fibroids and polyps. 

The Age a Girl Gets Her First Period

Menarche is another name for the beginning of menstruation. In the United States, the average age a girl starts menstruating is 12.However, this does not mean that all girls start at the same age. A girl can begin menstruating anytime between the ages of 8 and 16. Menstruation will not occur until all parts of a girl's reproductive system have matured and are working together.

How Long Does a Woman Have Periods?

Women usually continue having periods until menopause. Menopause occurs around the age of 51.This means that you are no longer ovulating (producing eggs) and therefore can no longer become pregnant.

Like menstruation, menopause can vary from woman to woman and may take several years to occur. Some women have early menopause because of surgery or other treatment types, or even illness.

When to See a Healthcare Provider About Your Period

You should consult your healthcare provider for the following:

  • If you have not started menstruating by the age of 16
  • If your period has suddenly stopped
  • If you are bleeding for more days than usual
  • If you are bleeding excessively
  • If you suddenly feel sick after using tampons
  • If you bleed between periods (more than just a few drops)
  • If you have severe pain during your period

How Often Should I Change My Pad/Tampon?

Sanitary napkins (pads) should be changed as often as necessary, generally before the pad is soaked with menstrual flow. Tampons should be changed at least every 4-8 hours. Make sure you use the lowest absorbency of tampon needed for your flow. 

If you experience any of the following symptoms while you are menstruating and using tampons, you should contact your healthcare provider immediately:

  • Sudden high fever
  • Muscle aches
  • Diarrhea
  • Dizziness and/or fainting
  • Sunburn-like rash
  • Sore throat
  • Bloodshot eyes
6 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Barbieri RL. The endocrinology of the menstrual cycle. Methods Mol Biol. 2014;1154:145-69. doi:10.1007/978-1-4939-0659-8_7

  2. Heiman DL. Amenorrhea: Evaluation and Treatment. American Family Physician.

  3. Bernardi M, Lazzeri L, Perelli F, Reis FM, Petraglia F. Dysmenorrhea and related disorders. F1000Res. 2017;6:1645. doi:10.12688/f1000research.11682.1

  4. Whitaker L, Critchley HO. Abnormal uterine bleeding. Best Pract Res Clin Obstet Gynaecol. 2016;34:54-65. doi:10.1016/j.bpobgyn.2015.11.012c

  5. Adams hillard PJ. Menstruation in adolescents: what's normal?. Medscape J Med. 2008;10(12):295.

  6. Gold EB. The timing of the age at which natural menopause occurs. Obstet Gynecol Clin North Am. 2011;38(3):425-40. doi:10.1016/j.ogc.2011.05.002

Additional Reading
  • The National Women's Health Information Center - NWHIC

By Tracee Cornforth
Tracee Cornforth is a freelance writer who covers menstruation, menstrual disorders, and other women's health issues.