An Overview of Menstruation By Andrea Chisholm, MD - Reviewed by a board-certified physician. Updated September 19, 2016 Many old wives tales and cultural or religious beliefs overshadow solid medical knowledge. So, it is important that you understand what menstruation really is, how it works, and why it is important.What Is Menstruation?From your first period (menarche) until your periods stop with menopause, the sole purpose of your monthly cycle is to reproduce. If a fertilized egg does not implant in the wall of your uterus after ovulation, the lining sheds. This is your menstrual period. Menstruation happens every month because you did not get pregnant. A regular menses (or period) occurs, on average, every 28 days or about 14 days after a regular ovulation. When your body does not function properly to cause ovulation, then your menstruation does not come regularly.3 Things You May Not Know Your brain controls your period. Believe it or not, your uterus is more of a bystander in this monthly process. The main players are two structures in the brain—the hypothalamus and the pituitary gland—along with the ovaries. Technically, this is referred to as the hypothalamic-pituitary-gonadal axis. When the interactions of this neuroendocrine trio function properly, ovulation and (if pregnancy doesn’t result from fertilization of the released egg) menstruation happen at regular intervals. Article How to Tell if You're Having an Abnormal Period Article Why Am I Bleeding After Sex? Your period marks the start of a new menstrual cycle. Your menstruation is the cyclic shedding of the lining of your uterus so it seems like your menstruation would mark the end of your menstrual cycle. Even the common term for menstruation—"your period"—makes you think about something ending. But actually, your menstruation marks the first day of a new cycle. When your bleeding starts, your brain has already initiated the hormone changes to trigger a new cycle. This is really important to understand—especially if you are trying to keep track of when you ovulate. When you are tracking your menstrual cycle, you need to count the first day of menstruation as cycle day one. There is more to your menstrual cycle than just your period. A lot of hormonal changes happen in your body leading up to your period. These hormone changes happen in a predictable way every month and the change they cause in your body is called your menstrual cycle, which includes: Egg selection and lining build up. As your period begins and the built up lining from the previous cycle is shed, special parts of your brain produce hormones that stimulate your ovaries to release estrogen and prepare an egg for ovulation. Under the influence of the rising estrogen levels, the lining of your uterus, or endometrium, begins to thicken or proliferate. Ovulation. In response to another change in hormone levels from your brain, your ovary releases an egg (oocyte) and ovulation occurs. This usually happens on cycle day 14. Progesterone Domination. The follicle that released the egg now begins to shrink. It continues to produce estrogen but also begins to produce progesterone. It is called the corpus luteum. Although both estrogen and progesterone are produced during this part of the cycle, progesterone concentrations dominate. Under the influence of progesterone, the lining of the uterus begins to change in ways to prepare it for pregnancy. In the first half of the cycle, the now built up lining becomes thicker and more complex with glands, blood vessels, and tissue swelling. These are all changes that prepare the uterine lining for the process of implantation and pregnancy. If implantation of a fertilized egg does not occur, the corpus luteum in the ovary continues to shrink away. Additionally, estrogen and progesterone levels continue to fall. When this happens, the blood vessels that expanded in the thickened lining constrict and cut off blood flow. The thickened lining, now without blood flow to support it, dies and is shed from the uterus. Article The Deadly Effects of Improperly Used Tampons Article Do You Really Know What Happens During Your Menstrual Cycle? Every Period May Not Be the SameObviously, your menstrual cycle is unique to you. How much you bleed, when you start, and for how long is unlike anyone else. But, it is also common and very normal for your own menstruation to change from month to month. A normal range for menstruation is every 21 to 35 days. Depending on the month, your period may come a few days early/late or your menstrual flow may be heavy/light. Many factors can influence the hormone changes in your body, including:StressExerciseWeight gain/lossTravel Illness Some women's cycles are more sensitive to fluctuations in hormone levels than others. Although it is normal for your menstruation to vary, it is also normal for it to stay completely regular. No Menstruation RestrictionsA normal period is not an illness or a disability. There is no medical reason to limit your physical activity during your period. You can do anything you would do off your period when you are on your period. This includes swimming, yoga, and all extreme sports. There is actually some evidence to suggest that your athletic performance may even be better during your period. It is also completely safe to have sex during menstruation.That said, some women have very heavy bleeding and/or very painful periods. This is not normal. If you are not participating in your normal activities or if you are missing work/school because of painful periods or heavy bleeding, you need to discuss this with your doctor.Keeping It CleanThere are many options to help you manage your menstrual flow. You may choose a feminine hygiene product based on convenience, comfort, or lifestyle. Whatever product you chose, it is important to change them frequently. You should consider avoiding products that contain fragrance or perfume as they can be very irritating.Some women feel they need to clean out their vagina after their monthly menstruation by using a douche. Not only is this not necessary, it is actually harmful. When you douche, you actually kill off the good bacteria in your vagina that keeps it clean and healthy. Article Everything You Ever Needed To Know About Menstruation Article I Haven't Had My Period for Months and I'm Not Pregnant. What Gives? Skipped MenstruationOnce you've started having regular periods, missing your monthly menstruation could be a sign of an underlying medical problem. If you are having sex, the most common cause of a missed period is pregnancy. You should consider taking a pregnancy test if you have missed your period.It can be normal to miss a period occasionally. This usually means that you didn't ovulate earlier in your menstrual cycle. The same things that can influence your menstrual flow, like stress and exercise, can influence your ovulation. And as long as you have determined that you are not pregnant, it is ok to wait another month to see if your period comes. If you miss your menstruation for two or three months in a row, you should talk to your doctor. A Word From VerywellMenstruation is a normal function of a woman's body. You should not be ashamed about your period. And your period shouldn't interfere with your lifestyle. If you are having problem periods, you should talk to your doctor. Your menstruation is not a reason to stop living well. Source:American College of Obstetricians & Gynecologists. (2013). Practice Bulletin No. 136. Management of abnormal uterine bleeding associated with ovulatory dysfunction. Obstet Gynecol. 122(1):176–85.