Menstruation

Raising awareness for menstruation as a global issue: World Menstrual Hygiene Day celebration in India

Menstruation (also known as a period and many other colloquial terms), is the regular discharge of blood and mucosal tissue (known as menses) from the inner lining of the uterus through the vagina. The menstrual cycle occurs due to the rise and fall of hormones. This cycle results in the thickening of the lining of the uterus, and the growth of an egg, (which is required for pregnancy). The egg is released from an ovary around day fourteen in the cycle; the thickened lining of the uterus provides nutrients to an embryo after implantation. If implantation does not occur, the lining is released in what is known as menstruation.[1]

In humans, the first period, a point in time known as menarche, usually begins between the ages of 12 and 15,[2] although menstruation may occasionally start as young as 8 years and still be considered normal.[1] The average age of the first period is generally later in the developing world, and earlier in the developed world.[3] The typical length of time between the first day of one period and the first day of the next is 21 to 45 days in young women, and 21 to 31 days in adults (an average of 28 days).[1][3] Bleeding usually lasts around 2 to 7 days. Periods stop during pregnancy and typically do not resume during the initial months of breastfeeding.[1] Menstruation stops occurring after menopause, which usually occurs between 45 and 55 years of age.[4]

Up to 80% of women do not experience problems sufficient to disrupt daily functioning as a result of menstruation, although they may report having some issues prior to menstruation. Symptoms interfere with normal life, qualifying as premenstrual syndrome, in 20 to 30% of women. In 3 to 8%, symptoms are severe.[5] These include acne, tender breasts, bloating, feeling tired, irritability, and mood changes.[6] A lack of periods, known as amenorrhea, is when periods do not occur by age 15 or have not occurred in 90 days.[1] Other experiences during the menstrual cycle include painful periods and abnormal bleeding such as bleeding between periods or heavy bleeding.[1]

Menstruation occurs in other animals;[7][8] most female mammals have an estrous cycle, but not all have a menstrual cycle.

Diagram illustrating how the uterus lining builds up and breaks down during the menstrual cycle

The first menstrual period occurs after the onset of pubertal growth, and is called menarche. The average age of menarche is 12 to 15.[2][9] However, it may start as early as eight.[1] The average age of the first period is generally later in the developing world, and earlier in the developed world.[3][10] The average age of menarche has changed little in the United States since the 1950s.[3]

Menstruation is the most visible phase of the menstrual cycle and its beginning is used as the marker between cycles. The first day of menstrual bleeding is the date used for the last menstrual period (LMP). The typical length of time between the first day of one period and the first day of the next is 21 to 45 days in young women, and 21 to 31 days in adults.[1][3] The average length is 28 days; one study estimated it at 29.3 days.[11] The variability of menstrual cycle lengths is highest for women under 25 years of age and is lowest, that is, most regular, for ages 25 to 39.[12] The variability increases slightly for women aged 40 to 44.[12]

Perimenopause is when a woman's fertility declines, and menstruation occurs less regularly in the years leading up to the final menstrual period, when a woman stops menstruating completely and is no longer fertile. The medical definition of menopause is one year without a period and typically occurs between 45 and 55 in Western countries.[4][13] Menopause before age 45 is considered premature in industrialized countries.[14] Like the age of menarche, the age of menopause is largely a result of cultural and biological factors.[dubious ][failed verification] Illnesses, certain surgeries, or medical treatments may cause menopause to occur earlier than it might have otherwise.[15]

During pregnancy and for some time after childbirth, menstruation does not occur. The average length of postpartum amenorrhoea is longer when breastfeeding; this is termed lactational amenorrhoea.[medical citation needed]

The average volume of menstrual fluid during a monthly menstrual period is 35 milliliters (2.4 tablespoons of menstrual fluid) with 10–80 milliliters (1–6 tablespoons of menstrual fluid) considered typical. Menstrual fluid is the correct name for the flow, although many people prefer to refer to it as menstrual blood. Menstrual fluid is reddish-brown, a slightly darker color than venous blood.[13]

About half of menstrual fluid is blood. This blood contains sodium, calcium, phosphate, iron, and chloride, the extent of which depends on the woman. As well as blood, the fluid consists of cervical mucus, vaginal secretions, and endometrial tissue. Vaginal fluids in menses mainly contribute water, common electrolytes, organ moieties, and at least 14 proteins, including glycoproteins.[16]

Many women and girls notice blood clots during menstruation. These appear as clumps of blood that may look like tissue. If there was a miscarriage or a stillbirth, examination under a microscope can confirm if it was endometrial tissue or pregnancy tissue (products of conception) that was shed.[17] Sometimes menstrual clots or shed endometrial tissue is incorrectly thought to indicate an early-term miscarriage of an embryo. An enzyme called plasmin – contained in the endometrium – tends to inhibit the blood from clotting.[medical citation needed]

The amount of iron lost in menstrual fluid is relatively small for most women.[better source needed][18] In one study, premenopausal women who exhibited symptoms of iron deficiency were given endoscopies. 86% of them actually had gastrointestinal disease and were at risk of being misdiagnosed simply because they were menstruating.[non-primary source needed][19] Heavy menstrual bleeding, occurring monthly, can result in anemia.[medical citation needed]

In most women, various physical changes are brought about by fluctuations in hormone levels during the menstrual cycle. This includes muscle contractions of the uterus (menstrual cramping) that can precede or accompany menstruation. Some may notice bloating, changes in sex drive, fatigue, breast tenderness, headaches, or irritability before the onset of their period.[21][22][23] It is unclear if the breast discomfort and bloating is related to electrolyte changes or water retention.[24] Some women have mild or no symptoms before the onset of their periods.[22] A healthy diet, reduced consumption of salt, caffeine and alcohol, and regular exercise may be effective for women in controlling water retention.[unreliable medical source?][25] Severe symptoms that disrupt daily activities and functioning may be diagnosed as premenstrual dysphoric disorder.[22]

Many women experience painful cramps, also known as dysmenorrhea, during menstruation.[26] Among adult women, that pain is severe enough to affect daily activity in only 2%–28%.[27]

Painful menstrual cramps that result from an excess of prostaglandin release are referred to as primary dysmenorrhea. Primary dysmenorrhea usually begins within a year or two of menarche, typically with the onset of ovulatory cycles.[better source needed][28] Treatments that target the mechanism of pain include non-steroidal anti-inflammatory drugs (NSAIDs) and hormonal contraceptives. NSAIDs inhibit prostaglandin production. With long-term treatment, hormonal birth control reduces the amount of uterine fluid/tissue expelled from the uterus. Thus resulting in shorter, less painful menstruation.[29] These drugs are typically more effective than treatments that do not target the source of the pain (e.g. acetaminophen).[30] Risk factors for primary dysmenorrhea include: early age at menarche, long or heavy menstrual periods, smoking, and a family history of dysmenorrhea.[28] Regular physical activity may limit the severity of uterine cramps.[28][31]

For many women, primary dysmenorrhea gradually subsides in late second generation. Pregnancy has also been demonstrated to lessen the severity of dysmenorrhea, when menstruation resumes. However, dysmenorrhea can continue until menopause. 5–15% of women with dysmenorrhea experience symptoms severe enough to interfere with daily activities.[28]

Secondary dysmenorrhea is the diagnosis given when menstruation pain is a secondary cause to another disorder. Conditions causing secondary dysmenorrhea include endometriosis, uterine fibroids, and uterine adenomyosis. Rarely, congenital malformations, intrauterine devices, certain cancers, and pelvic infections cause secondary dysmenorrhea.[28] If the pain occurs between menstrual periods, lasts longer than the first few days of the period, or is not adequately relieved by the use of non-steroidal anti-inflammatory drugs (NSAIDs) or hormonal contraceptives, women should be evaluated for secondary causes of dysmenorrhea. [32]

When severe pelvic pain and bleeding suddenly occur or worsen during a cycle, the woman or girl should be evaluated for ectopic pregnancy and spontaneous abortion. This evaluation begins with a pregnancy test and should be done as soon as unusual pain begins, because ectopic pregnancies can be life‑threatening.[33]

In some cases, stronger physical and emotional or psychological sensations may interfere with normal activities, and include menstrual pain (dysmenorrhea), migraine headaches, and depression. Dysmenorrhea, or severe uterine pain, is particularly common for girls and young women (one study found that 67.2% of girls aged 13–19 have it).[34]

Some women experience emotional disturbances starting one or two weeks before their period, and stopping within a few days of the period starting.[6][35] Symptoms may include mental tension, irritability, mood swings, and crying spells. Problems with concentration and memory may occur.[6] There may also be depression or anxiety.[6]

These symptoms can be severe enough to impact a person's performance at work, school, and in every day activities in a small percentage of women.[5] Greater loss in workplace productivity, quality of life, and greater healthcare costs occur in those with moderate to severe symptoms in comparison to those without these symptoms.[36] This is part of premenstrual syndrome (PMS) and is estimated to occur in 20 to 30% of women.[5] In 3 to 8% it is severe.[5]

More severe symptoms of anxiety or depression may be signs of premenstrual dysphoric disorder (PMDD). This disorder is listed in the DSM-5 as a depressive disorder.[36] Rarely, in individuals who are susceptible, menstruation may be a trigger for menstrual psychosis.[medical citation needed]

The different phases of the menstrual cycle can correlate with women's moods. In some cases, hormones released during the menstrual cycle can cause behavioral changes in women; mild to severe mood changes can occur.[better source needed][38]

Sexual intercourse during menstruation does not cause damage in and of itself, but the woman's body is more vulnerable during this time. Vaginal pH is higher and thus less acidic than normal,[39] the cervix is lower in its position, the cervical opening is more dilated, and the uterine endometrial lining is absent, thus allowing organisms direct access to the bloodstream through the numerous blood vessels that nourish the uterus. All these conditions increase the chance of infection during menstruation.[40]

Sexual feelings and behaviors change during the menstrual cycle. Before and during ovulation, high levels of estrogen and androgens result in women having a relatively increased interest in sexual activity.[41] Unlike other mammals, women may show interest in sexual activity across all days of the menstrual cycle, regardless of fertility.[42]

Some women with neurological conditions experience increased activity of their conditions at about the same time during each menstrual cycle. For example, drops in estrogen levels have been known to trigger migraines,[medical citation needed] especially when the woman who suffers migraines is also taking the birth control pill. Many women with epilepsy have more seizures in a pattern linked to the menstrual cycle; this is called "catamenial epilepsy".[43] Different patterns seem to exist (such as seizures coinciding with the time of menstruation, or coinciding with the time of ovulation), and the frequency with which they occur has not been firmly established. Using one particular definition, one group of scientists found that around one-third of women with intractable partial epilepsy has catamenial epilepsy.[non-primary source needed][43][44][45] An effect of hormones has been proposed, in which progesterone declines and estrogen increases would trigger seizures.[46] Recently, studies have shown that high doses of estrogen can cause or worsen seizures, whereas high doses of progesterone can act like an antiepileptic drug.[47]

Research indicates that women have a significantly higher likelihood of anterior cruciate ligament injuries in the pre-ovulatory stage, than post-ovulatory stage.[48]

The most fertile period (the time with the highest likelihood of pregnancy resulting from sexual intercourse) covers the time from some 6 days before until 2 days after ovulation.[49] These approximately 8 days in a 28‑day cycle with a 14‑day luteal phase, corresponds to the second and the beginning of the third week. A variety of methods have been developed to help individual women estimate the relatively fertile and the relatively infertile days in the cycle; these systems are called fertility awareness.[medical citation needed]

There are many fertility testing and fertility awareness methods. Fertility awareness methods that rely on cycle length records alone are called calendar-based methods.[50][51] A woman's fertility is also affected by her age.[52]

Infrequent or irregular ovulation is called oligoovulation.[53] The absence of ovulation is called anovulation. Normal menstrual flow can occur without ovulation preceding it: an anovulatory cycle. In some cycles, follicular development may start but not be completed; nevertheless, estrogens will be formed and stimulate the uterine lining. Anovulatory flow resulting from a very thick endometrium caused by prolonged, continued high estrogen levels is called estrogen breakthrough bleeding. Anovulatory bleeding triggered by a sudden drop in estrogen levels is called withdrawal bleeding.[full citation needed][54] Anovulatory cycles commonly occur before menopause (perimenopause) and in women with polycystic ovary syndrome.[55]

Very little flow (less than 10 ml) is called hypomenorrhea. Regular cycles with intervals of 21 days or fewer are polymenorrhea; frequent but irregular menstruation is known as metrorrhagia. Sudden heavy flows or amounts greater than 80 ml are termed menorrhagia.[56] Heavy menstruation that occurs frequently and irregularly is menometrorrhagia. The term for cycles with intervals exceeding 35 days is oligomenorrhea.[57] Amenorrhea refers to more than three[56] to six[57] months without menses (while not being pregnant) during a woman's reproductive years. The term for painful periods is dysmenorrhea.

There is a wide spectrum of differences in how women experience menstruation. There are several ways that someone's menstrual cycle can differ from the norm:

Dysfunctional uterine bleeding is a hormonally caused bleeding abnormality. Dysfunctional uterine bleeding typically occurs in premenopausal women who do not ovulate normally (i.e. are anovulatory). All these bleeding abnormalities need medical attention; they may indicate hormone imbalances, uterine fibroids, or other problems. As pregnant women may bleed, a pregnancy test forms part of the evaluation of abnormal bleeding.[medical citation needed]

Women who had undergone female genital mutilation (particularly type III- infibulation) a practice common in parts of Africa, may experience menstrual problems, such as slow and painful menstruation, that is caused by the near-complete sealing off of the vagina.[58]

Menstruating women manage menstruation primarily by wearing menstrual products such as tampons, napkins or menstrual cups to catch the menstrual blood.

Due to poverty, some cannot afford commercial feminine hygiene products.[59][60] Instead, they use materials found in the environment or other improvised materials. Absorption materials that may be used by women who cannot afford anything else include: sand, ash, small hole in earth,[61] cloth, whole leaf, leaf fiber (such as water hyacinth, banana, papyrus, cotton fibre), paper (toilet paper, re-used newspaper, brown paper bags, pulped and dried paper),[62] animal pelt (such as goat skin),[61] double layer of underwear, socks, skirt, or sari.[60][63]

“Period poverty” is a global issue affecting women and girls who do not have access to safe, hygienic sanitary products.[64]

Menstrual products (also called "feminine hygiene" products) are made to absorb or catch menstrual blood. A number of different products are available - some are disposable, some are reusable. Where women can afford it, items used to absorb or catch menses are usually commercially manufactured products.

The elements of a tampon with applicator. Left: the bigger tube ("penetrator"). Center: cotton tampon with attached string. Right: the narrower tube.

Menstrual hygiene products are considered by many states within the United States as "tangible individual property" resulting in additional sales tax. This additional tax increases the overall price and further limits accessibility to menstrual hygiene products to lower income women. These products are classified as medical devices but are not eligible for purchase through government funded assistance programs.[65] The Scottish government have in 2019 begun providing free sanitary products for poorer students at schools, with hopes that this will be rolled out across the entire nation.[66][67]

passed unanimously and it is in its final stage on November 24, 2020. The bill was passed after 4 years of campaign spearheaded by Monica Lennon. The act will impose legal duty on the local authorities to make period products available for free of cost. With this act Scotland became the first country in the world to provide universal access to free period products.[68][69]

In developing countries, women experience the lack of access to affordable menstrual hygiene products in addition to a lack of access to other services such as sanitation and waste disposal systems needed to manage their menstrual cycles. Lack of access to waste disposal leads women to throw used products in toilet systems, pit latrines, or discarded in to open areas such as bodies of water. These practices pose dangers to workers who handle these wastes as it increases possible exposure to bloodborne infections in soaked menstrual products and exposure to chemicals found in menstrual hygiene products. Inappropriate disposal also creates pressures on sanitation systems as menstrual hygiene products create sewage blockages.[59] The effects of these inadequate facilities has been shown to have social effects on girls in developing countries leading to school absenteeism.[70]

The most common treatment for menstrual cramps are non-steroidal anti-inflammatory drugs (NSAIDs). NSAIDs can be used to reduce moderate to severe pain, and all appear similar.[71] About 1 in 5 women do not respond to NSAIDs and require alternative therapy, such as simple analgesics or heat pads.[72] Other medications for pain management include aspirin or paracetamol and combined oral contraceptives. Although combined oral contraceptives may be used, there is insufficient evidence for the efficacy of intrauterine progestogens.[73]

One review found tentative evidence that acupuncture may be useful, at least in the short term.[74] Another review found insufficient evidence to determine an effect.[75]

Menstruation can be delayed by the use of progesterone or progestins. For this purpose, oral administration of progesterone or progestin during cycle day 20 has been found to effectively delay menstruation for at least 20 days, with menstruation starting after 2–3 days have passed since discontinuing the regimen.[76]

Half-used blister pack of a combined oral contraceptive. The white pills are placebos, mainly for the purpose of reminding the woman to continue taking the pills.

Hormonal contraception affects the frequency, duration, severity, volume, and regularity of menstruation and menstrual symptoms.

The most common form of hormonal contraception is the combined birth control pill, which contains both estrogen and progestogen. It is typically taken in 28-day cycles, 21 hormonal pills with either a 7-day break from pills, or 7 placebo pills during which the woman menstruates. Although the primary function of the pill is to prevent pregnancy, it may be used to improve , such as polycystic ovary syndrome (PCOS), endometriosis, adenomyosis, amenorrhea, menstrual cramps, menstrual migraines, menorrhagia (excessive menstrual bleeding), menstruation-related or fibroid-related anemia and dysmenorrhea (painful menstruation) by creating regularity in menstrual cycles and reducing overall menstrual flow.[77][78]

Using the combined birth control pill, it is also possible for a woman to delay or completely eliminate menstrual periods, a practice called menstrual suppression.[79] Some women do this simply for convenience in the short-term,[80] while others prefer to eliminate periods altogether when possible. This can be done either by skipping the placebo pills, or using an extended cycle combined oral contraceptive pill, which were first marketed in the U.S. in the early 2000s. This continuous administration of active pills without the placebo can lead to the achievement of amenorrhea in 80% of users within 1 year of use.[81]

When the first birth control pill was being developed, the researchers were aware that they could use the contraceptive to space menstrual periods up to 90 days apart, but they settled on a 28-day cycle that would mimic a natural menstrual cycle and produce monthly periods. The intention behind this decision was the hope of the inventor, John Rock, to win approval for his invention from the Roman Catholic Church. That attempt failed, but the 28-day cycle remained the standard when the pill became available to the public.[82]

Injections such as depo-provera (DMPA) became available in the 1960s and later became used to also achieve amenorrhea. A majority of patients will achieve amenorrhea within 1 year of initiating DMPA therapy. DMPA therapy is typically successful in achieving amenorrhea but also has side effects of decreased bone mineral density that must be considered before beginning therapy.[81]

Levonorgestrel intrauterine devices have also been used been shown to induce amenorrhea. The lower dose device has a lower rate of achieving amenorrhea compared to the higher dose device where 50% of users have been found to achieve amenorrhea within 1 year of use. A concern for usage of these devices is the invasive administration and initial breakthrough bleeding while utilizing these devices however they have the advantage of the most infrequent dosing schedule of every 5 years. Use of intrauterine devices have also shown to reduce menorrhagia and dysmenorrhea.[81][83]

When using the subdermal progestin only implants, unpredictable bleeding continues and amenorrhea is not commonly achieved amongst patients.[81]Progestogen-only contraceptive pills (sometimes called the 'mini pill') are taken continuously without a 7-day span of using placebo pills, and therefore menstrual periods are less likely to occur than with the combined pill with placebo pills. However, disturbance of the menstrual cycle is common with the mini-pill; 1/3-1/2 of women taking it will experience prolonged periods, and up to 70% experience break-through bleeding (metrorrhagia). Irregular and prolonged bleeding is the most common reason that women discontinue using the mini pill.[84]

While some forms of birth control do not affect the menstrual cycle, hormonal contraceptives work by disrupting it. Progestogen negative feedback decreases the pulse frequency of gonadotropin-releasing hormone (GnRH) release by the hypothalamus, which decreases the release of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) by the anterior pituitary. Decreased levels of FSH inhibit follicular development, preventing an increase in estradiol levels. Progestogen negative feedback and the lack of estrogen positive feedback on LH release prevent a mid-cycle LH surge. Inhibition of follicular development and the absence of a LH surge prevent ovulation.[85][86][87]

The degree of ovulation suppression in progestogen-only contraceptives depends on the progestogen activity and dose. Low dose progestogen-only contraceptives—traditional progestogen only pills, subdermal implants Norplant and Jadelle, and intrauterine system Mirena—inhibit ovulation in about 50% of cycles and rely mainly on other effects, such as thickening of cervical mucus, for their contraceptive effectiveness.[88] Intermediate dose progestogen-only contraceptives—the progestogen-only pill Cerazette and the subdermal implant Nexplanon—allow some follicular development but more consistently inhibit ovulation in 97–99% of cycles. The same cervical mucus changes occur as with very low-dose progestogens. High-dose, progestogen-only contraceptives—the injectables Depo-Provera and Noristerat—completely inhibit follicular development and ovulation.[88]

Combined hormonal contraceptives include both an estrogen and a progestogen. Estrogen negative feedback on the anterior pituitary greatly decreases the release of FSH, which makes combined hormonal contraceptives more effective at inhibiting follicular development and preventing ovulation. Estrogen also reduces the incidence of irregular breakthrough bleeding.[85][86][87] Several combined hormonal contraceptives—the pill, NuvaRing, and the contraceptive patch—are usually used in a way that causes regular withdrawal bleeding. In a normal cycle, menstruation occurs when estrogen and progesterone levels drop rapidly.[full citation needed][89] Temporarily discontinuing use of combined hormonal contraceptives (a placebo week, not using patch or ring for a week) has a similar effect of causing the uterine lining to shed. If withdrawal bleeding is not desired, combined hormonal contraceptives may be taken continuously, although this increases the risk of breakthrough bleeding.[medical citation needed]

There is debate among medical researchers about the potential long-term impacts of these practices upon women's health. Some researchers point to the fact that historically, women and girls had far fewer menstrual periods throughout their lifetimes, a result of shorter life expectancies, as well as a greater length of time spent pregnant or breast-feeding, which reduced the number of periods they experienced.[90] There is also the advantage of inducing menstrual suppression amongst people with extreme cognitive and physical disabilities who may not be able to properly manage their menstrual hygiene even with the use of a caregiver.[91] On the other hand, some researchers believe there is a greater potential for negative impacts from exposing women and girls perhaps unnecessarily to regular low doses of synthetic hormones over their reproductive years.[92] There is limited evidence that the act of menstrual suppression directly causes physiologic harm and the primary disadvantages shown to be associated with menstrual suppression are due to side effects of the methods used to achieve amenorrhea.[81][91]

Breastfeeding causes negative feedback to occur on pulse secretion of gonadotropin-releasing hormone (GnRH) and luteinizing hormone (LH). Depending on the strength of the negative feedback, breastfeeding women may experience complete suppression of follicular development, follicular development but no ovulation, or normal menstrual cycles may resume.[93] Suppression of ovulation is more likely when suckling occurs more frequently.[94] The production of prolactin in response to suckling is important to maintaining lactational amenorrhea.[95] On average, women who are fully breastfeeding whose infants suckle frequently experience a return of menstruation at fourteen and a half months postpartum. There is a wide range of response among individual breastfeeding women, however, with some experiencing return of menstruation at two months and others remaining amenorrheic for up to 42 months postpartum.[96]

Many religions have menstruation-related traditions, for example: Islam prohibits sexual contact with women during menstruation in the 2nd chapter of the Quran. Some scholars argue that menstruating women are in a state in which they are unable to maintain wudhu, and are therefore prohibited from touching the Arabic version of the Qur'an. Other biological and involuntary functions such as vomiting, bleeding, sexual intercourse, and going to the bathroom also invalidate one's wudhu.[97] In Judaism, a woman during menstruation is called Niddah and may be banned from certain actions. For example, the Jewish Torah prohibits sexual intercourse with a menstruating woman.[98] In Hinduism, menstruating women are traditionally considered ritually impure and given rules to follow.[99][100]

Menstruation education is frequently taught in combination with sex education at school in Western countries, although girls may prefer their mothers to be the primary source of information about menstruation and puberty.[101] Information about menstruation is often shared among friends and peers, which may promote a more positive outlook on puberty.[102] The quality of menstrual education in a society determines the accuracy of people's understanding of the process.[103] In many Western countries where menstruation is a taboo subject, girls tend to conceal the fact that they may be menstruating and struggle to ensure that they give no sign of menstruation.[103] Effective educational programs are essential to providing children and adolescents with clear and accurate information about menstruation. Schools can be an appropriate place for menstrual education to take place.[104] Programs led by peers or third-party agencies are another option.[104] Low-income girls are less likely to receive proper sex education on puberty, leading to a decreased understanding of why menstruation occurs and the associated physiological changes that take place. This has been shown to cause the development of a negative attitude towards menstruation.[105]

In some cultures, mainly in developing countries, women were isolated during menstruation due to menstrual taboos.[106] This is because they are seen as unclean, dangerous, or bringing bad luck to those who encounter them. These practices are common in parts of South Asia, especially in Nepal. Chhaupadi is a social practice that occurs in the western part of Nepal for Hindu women, which prohibits a woman from participating in everyday activities during menstruation. Women are considered impure during this time, and are kept out of the house and have to live in a shed. Although chhaupadi was outlawed by the Supreme Court of Nepal in 2005, the tradition is slow to change.[107][108] Women and girls in cultures which practice such seclusion are often confined to menstruation huts, which are places of isolation used by cultures with strong menstrual taboos. The practice has recently come under fire due to related fatalities. Nepal criminalized the practice in 2017 after deaths were reported after the elongated isolation periods, but “the practice of isolating menstruating women and girls continues.“[109]

Even though the average length of the human menstrual cycle is similar to that of the lunar cycle, in modern humans there is no relation between the two.[110] The relationship is believed to be a coincidence.[111][112] Light exposure does not appear to affect the menstrual cycle in humans.[7] A meta-analysis of studies from 1996 showed no correlation between the human menstrual cycle and the lunar cycle,[113] nor did data analysed by period-tracking app Clue, submitted by 1.5m women, of 7.5m menstrual cycles, however the lunar cycle and the average menstrual cycle were found to be basically equal in length.[114]

Dogon villagers did not have electric lighting and spent most nights outdoors, talking and sleeping, so they were apparently an ideal population for detecting a lunar influence; none was found.[115]

Beginning in 1971, some research suggested that menstrual cycles of cohabiting women and girls became synchronized (menstrual synchrony).[116] Subsequent research has called this hypothesis into question.[117] A 2013 review concluded that menstrual synchrony likely does not exist.[118]

Some countries, mainly in Asia, have menstrual leave to provide women with either paid or unpaid leave of absence from their employment while they are menstruating.[119] Countries with policies include Japan, Taiwan, Indonesia, and South Korea.[120][121] The practice is controversial due to concerns that it bolsters the perception of women as weak, inefficient workers,[119] as well as concerns that it is unfair to men,[122][123] and that it furthers gender stereotypes and the medicalization of menstruation.[120]

There are a growing number of activists who are working to fight for menstrual equity.[citation needed] At 16-years-old, Nadya Okamoto founded the organization, PERIOD, and wrote the book Period Power: a Manifesto for the Menstrual Movement.[124]

The word "menstruation" is etymologically related to "moon". The terms "menstruation" and "menses" are derived from the Latin mensis (month), which in turn relates to the Greek mene (moon) and to the roots of the English words month and moon.[125]