Menstruation is the monthly shedding of tissue and blood from the uterus. It is the most visible part of the menstrual cycle. Girls usually begin menstruating around the age of 12 or 13 years, but can begin menstruating as young as age 9.

The menstrual cycle is a result of the complex interaction of several hormones. Many hormones are involved, but the four major ones are follicle stimulating hormone (FSH), luteinizing hormone (LH), estrogen and progesterone. The interaction of these hormones generally affects two areas of the reproductive system the most: the uterus and the egg follicles in the ovaries.

The average menstrual cycle lasts about 28 days, but may range from 21 to 35 days. The menstrual period usually lasts about five days each month for most girls. During the menstrual period, blood comes out from the vagina. The amount ranges from a couple of tablespoons to a half-cup or more daily. Girls use various products to absorb menstrual flow, including panty liners, tampons and pads.

During the first few years of menstruation, a girl’s period may be irregular. Some girls may only have three or four periods a year. Within about two years of first menstruating, girls generally develop a more regular monthly cycle.

Menstruation can cause problems ranging from mild discomfort to pain. Some girls have physical and emotional symptoms before menstruating that are severe enough to be classified as premenstrual syndrome (PMS). In addition, many girls experience cramps during menstruation. These cramps tend to affect the lower abdomen, but they may also affect the back or the thighs. 

Several other problems may be associated with menstruation. Pain during menstruation is called dysmenorrhea. Amenorrhea is the lack of menstruation. Very heavy bleeding during menstruation is called menorrhagia, which is usually due to an imbalance between levels of estrogen and progesterone.

In some cases, discomfort associated with menstruation can be treated with over-the-counter pain relievers or other techniques, such as warm baths. However, more serious menstrual problems may require prescription medications, surgery or both.

Parents and girls may feel uncomfortable about the prospect of discussing menstruation. However, it is important that this conversation take place before a girl’s teenage years and preferably during middle childhood.