Menstruation, from menarche to menopause, visits women monthly for about 35 years—making it a long-time companion. It refers to the regular vaginal bleeding that occurs monthly after a woman reaches sexual maturity.
Ancient Chinese believed menstruation "follows the waxing and waning of the moon, as reliable as the tides," hence its names "monthly visitor" or "monthly water."
Modern women have their own colloquial terms, such as "period," "that time of the month," or "Aunt Flo."
A girl's first menstrual cycle is called menarche. The average age for menarche is around 14, with some experiencing it as early as 11-12 and others as late as 15-16. If menstruation hasn't started by age 16, it warrants attention.Menstruation typically ceases around age 49, known as menopause. The menstrual period lasts approximately 35 years, occurring regularly except during pregnancy and lactation. The cycle generally spans 28 days—roughly one month—hence the name "monthly flow." Variations within 7 days before or after are considered normal, meaning cycles should not fall below 21 days or exceed 35 days.
The duration of each menstrual flow is called the menstrual period, typically lasting 3-7 days, with most women experiencing 4-5 days. The average blood loss per cycle is 50-80 milliliters. Menstrual blood appears dark red, starting lighter in color before gradually deepening, and finally fading to a pale red before stopping.
Menstrual blood generally does not clot. Blood clotting occurs due to fibrin, but menstrual blood contains high levels of fibrinolytic enzymes that dissolve fibrin, preventing clotting. Menstrual blood is neither too thin nor too thick, contains no noticeable clots, and has no distinct odor.
Although menstruation should occur monthly, exceptions exist. A cycle occurring every two months is termed synmenorrhea; every three months is called oligomenorrhea or seasonal menstruation; annually is known as annual amenorrhea; and lifelong absence of menstruation with normal fertility is termed cryptomenorrhea. Menstruation typically ceases during pregnancy and lactation, though exceptions occur.A small number of women may experience menstruation during early pregnancy without harming the fetus; this is termed "stimulated menstruation" (jijing), or "prosperous pregnancy" (shengtai) or "impure pregnancy" (goutai). Similarly, a minority of women may menstruate monthly during lactation.
After menarche, young women may experience irregular menstrual cycles for a period. This is normal as long as no significant discomfort is present, and cycles typically become regular within about two years.
The Kidneys Are the Source of Menstruation
The Yellow Emperor's Classic of Internal Medicine states: "At seven years of age, a girl's kidney qi reaches its peak; her teeth change and her hair grows. At fourteen, the heavenly essence arrives, the Ren Meridian opens, the Tai Chong Meridian flourishes, and menstruation begins at regular intervals, enabling conception.At forty-seven, kidney qi reaches equilibrium, thus permanent teeth emerge and grow to full length; at fifty-seven, tendons and bones become firm, the body reaches peak vigor; at sixty-seven, the Yangming meridian declines, the complexion begins to wither, hair starts to fall; at seventy-seven, the three Yang meridians decline in the upper body, the complexion becomes fully withered, hair begins to turn white; at eighty-four, the Ren meridian becomes deficient, the Tai Chong meridian declines, the Tian Kui dries up, the passage to the earth ceases, thus the body deteriorates and bears no children."
A woman's sexual function, reproductive capacity, and menstruation are interconnected. The onset of menstruation signifies sexual maturity and the attainment of fertility, all governed by the kidneys. The prerequisites for menstruation are: abundant kidney qi, the arrival of Tian Gui, an open Ren Meridian, and a vigorous Tai Chong Meridian.
The kidneys are the foundation of innate constitution. The life information, energy, and substances inherited from parents are stored within the kidneys, forming the primordial driving force of life.After birth, as kidney qi continually flourishes, various physiological functions gradually mature. For women, this unfolds in seven-year cycles of rhythmic change. Driven by kidney qi: At age 7, teeth are replaced and hair grows thick; At age 14, sexual maturation occurs, secondary sexual characteristics emerge, and menstruation begins.The arrival of Tian Gui resembles what modern Western medicine refers to as the maturation of the gonads and the normal secretion of sex hormones. The onset of menstruation signifies the maturation of the ovaries, the ability to ovulate normally, and the attainment of reproductive capacity. The prerequisite for the arrival of Tian Gui is the abundance of kidney qi; that is, Tian Gui arrives only when kidney qi is vigorous.
The opening of the Ren Meridian and the abundance of the Tai Chong Meridian are also conditions for the onset of menstruation.The Tai Chong Meridian is synonymous with the Chong Meridian. Both the Ren and Chong Meridians belong to the Eight Extraordinary Vessels, holding significant importance for female reproductive function. Originating from the uterus, Traditional Chinese Medicine holds that "the Chong Meridian governs the sea of blood, while the Ren Meridian governs the uterus." Only when kidney qi is abundant, Tian Gui arrives, the Ren Meridian is unobstructed, and blood in the Chong Meridian is vigorous does menstruation occur, signifying reproductive capability.
Additionally, menstruation is fundamentally blood, formed upon the foundation of abundant blood. The kidneys govern the storage of essence, and essence and blood mutually generate each other. Sufficient kidney essence is also a source for the transformation of blood. If kidney essence is deficient, essence cannot transform into blood, potentially leading to scanty menstruation or even amenorrhea.Modern Western medical research has discovered that the kidneys secrete a hormone called erythropoietin. This hormone promotes the production of red blood cells in the blood and maintains their lifespan. If kidney function is impaired, affecting erythropoietin secretion, insufficient red blood cells are produced in the blood, and their lifespan is shortened, leading to anemia. This type of anemia is called renal anemia.Patients with chronic renal failure and uremia commonly develop renal anemia. From a Western medical perspective, the kidneys and blood are closely interconnected.