What Teen Girls Should Know About Having Periods

Get the facts on what happens during the menstrual cycle

The menstrual cycle is how a woman's body prepares for the possibility of pregnancy each month. A menstrual period is just one part of this cycle. A cycle's length is determined by counting from the first day of one period to the first day of the next period. The average menstrual cycle is 28 days long. However, a normal cycle can range anywhere from 21 to 35 days.

Young Woman with PMS
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What Happens During the Menstrual Cycle

During the menstrual cycle, an egg is released from the ovaries. While the egg is traveling down the fallopian tubes and towards the uterus, the uterus is building up a lining that consists of extra blood and tissue. The lining of the uterus will thicken and, if pregnancy occurs, blood vessels in the lining will enlarge to nourish the growing fetus.

If the egg becomes fertilized by a sperm cell, the egg will attach itself to the uterine wall and a fetus will begin to develop. If the egg goes unfertilized, the thick lining that builds up during the menstrual cycle is not needed and is shed during your period. The unfertilized egg either dissolves or is absorbed into the body. After the period ends, a new menstrual cycle begins.

What a Period Is

A period is a part of the menstrual cycle when the thick uterine lining and extra blood are shed through the vaginal canal. Periods can be light, moderate or heavy, and the menstrual blood that is shed can range from a few tablespoons to a 1/2 cup per period. This can vary from girl to girl, and it can vary from period to period for the same girl.

Many girls experience a light flow for the first day or two, then a heavier flow, followed by another light day. Some girls have a heavy flow on the first day. For the first few years after you start menstruating, your period may be very irregular.

How old is a girl when she gets her first period? 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. This time in a young woman's life is called "puberty."

How Long a Period Lasts

Because all girls are different, menstrual periods can vary from girl to girl. One girl might have a three-day period and another girl might have a seven-day period. It might take several years for a girl's period to become regular. One month the period might last four days, whereas the next month it might be six days.

Some women experience irregular periods for several years and might not ever be "regular." Some healthcare providers will prescribe birth control pills to help regulate your menstrual cycle. Talk to your practitioner to find out how you can regulate your cycle if it is irregular.

When to Change Pads or Tampons During a Period

Sanitary napkins (pads) should be changed as often as necessary before the pad is soaked with menstrual flow. Each woman decides for herself what is comfortable. Tampons should be changed every 4 to 8 hours. They should never be used for more than 8 hours.

Make sure that you use the lowest absorbency of tampon available. For example, do not use super absorbency on the lightest day of your period. This can put you at risk for Toxic Shock Syndrome (TSS). TSS is a rare but potentially deadly disease.

The risk of TSS can be lessened or avoided by not using tampons, or by alternating between tampons and pads during your period. If you experience any of the following symptoms while you are menstruating and using tampons, you should contact your healthcare provider immediately:

  • Sudden, unexplained, high fever
  • Muscle aches
  • Diarrhea
  • Dizziness and/or fainting
  • Sunburn-like rash
  • Sore throat
  • Bloodshot eyes

How Having a Period Affects Daily Activities

Your period should not affect your daily activities. You can continue to exercise, swim, bike ride and have fun. Some girls and women even find that exercising while they are having their menstrual period reduces or prevents stomach cramps and discomfort.

The easiest way to figure out when your period is going to begin is to keep track of it on a calendar. Mark the first day of your period each month. Now count the days between periods. Beginning with the first day you marked and count to the second day you marked. Do this for a few months and then you will be able to calculate how many days there usually are between your periods. This will help you prepare yourself for your period and keep you from being surprised.

Why a Period Might Be Skipped

There are several reasons why you might skip a period one month. If you have just started having your period, it might not come every month. If you are an older woman who is approaching menopause, (when your periods stop), you might also skip a period.

Excessive stress might cause you to skip a period. Stress and highly emotional times in your life may cause you to miss a period or two. If you are sick, you might also miss a period. If you miss more than a period or two (if you have been having regular periods previously), contact your healthcare provider.

Why Having a Period Might Stop

The absence of a menstrual period is called amenorrhea. This condition describes women who have not had a period in their teenage years or women who used to have a regular period that has stopped permanently. There are several causes of amenorrhea.

Pregnancy is the most common reason for a woman to stop having her menstrual period. There's also breastfeeding and extreme weight loss caused by serious illness, eating disorders or excessive exercising.

Gland problems (pituitary, thyroid, or adrenal) and reproductive problems may also have this effect. If your period has not started by the age of 16, or if you have stopped having your period, while you are still young, contact your healthcare provider.

Will You Have a Period for the Rest of Your Life?

No. A woman will no longer be able to reproduce once she reaches menopause. Menopause occurs around the age of 50. Menopause means that a woman is 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.

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 unbearable pain during your period
7 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. Reed BG. The Normal Menstrual Cycle and the Control of Ovulation. Endotext [Internet]. 

  2. UpToDate. Physiology of the Normal Menstrual Cycle.

  3. American College of Obstetricians and Gynecologists. Your First Period.

  4. US Food and Drug Administration. The facts on tampons and how to use them safely.

  5. Gottlieb M, Long B, Koyfman A. The Evaluation and Management of Toxic Shock Syndrome in the Emergency Department: A Review of the Literature. J Emerg Med. 2018;54(6):807-814. doi:10.1016/j.jemermed.2017.12.048

  6. Fourman LT, Fazeli PK. Neuroendocrine causes of amenorrhea--an update. J Clin Endocrinol Metab. 2015;100(3):812-24. doi:10.1210/jc.2014-3344

  7. Santoro N, Epperson CN, Mathews SB. Menopausal Symptoms and Their Management. Endocrinol Metab Clin North Am. 2015;44(3):497-515. doi:10.1016/j.ecl.2015.05.001

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