Common Myths About Periods That Persist—And the Facts Behind Them

The idea that periods are a form of purification or that menstrual blood contains harmful waste is rooted in cultural taboo, not biology. The uterine lining builds up each cycle under the influence of hormones to prepare for a potential pregnancy. When fertilization does not occur, that lining sheds — a healthy, regulated process. There is nothing inherently 'unclean' about this fluid, and treating it as such can contribute to stigma that discourages people from seeking appropriate care.

A widely cited 1971 study suggested that women living in close proximity synchronize their cycles through pheromone signals. However, multiple later studies using larger samples and more rigorous methods have failed to replicate this finding. Researchers have pointed out that given the natural variation in cycle length between individuals, apparent synchrony can occur by chance. The scientific consensus today treats the evidence for menstrual synchrony as inconclusive at best. For a broader look at how menstrual phase science translates — and sometimes doesn't — into practical guidance, see our article on cycle syncing and what research actually supports.

Dysmenorrhea — the medical term for painful periods — affects many menstruating people to varying degrees. Primary dysmenorrhea arises from prostaglandin-driven uterine contractions and is common. Secondary dysmenorrhea, however, is caused by identifiable conditions such as endometriosis, adenomyosis, or uterine fibroids. Endometriosis alone affects an estimated 1 in 10 people with a uterus, yet often goes undiagnosed for years partly because pain is normalized and dismissed. Anyone experiencing pain that interferes with school, work, or daily life should discuss it with a healthcare provider. Conditions like PCOS can also influence cycle patterns and warrant proper evaluation.

Combined hormonal contraceptives (such as the pill) work primarily by suppressing ovulation, which means no egg is released and no natural menstrual cycle is occurring. The bleed that happens during the pill-free or placebo days is a withdrawal bleed triggered by the drop in synthetic hormones. It was originally included partly to make the pill feel more familiar and natural. Medically, skipping this bleed by taking active pills continuously is considered safe for many people, though individual circumstances vary and a healthcare provider should guide any such decisions.

Sperm can survive in the reproductive tract for up to five days. For someone with a shorter menstrual cycle, ovulation can occur relatively soon after a period ends — meaning sperm present during menstruation could potentially fertilize an egg. This risk is higher for those with irregular or shorter cycles and lower (but not zero) for those with longer cycles. Relying on menstruation as a contraceptive method is not recommended by medical or reproductive health authorities.

There is no clinical evidence that exercising during a period is harmful. On the contrary, aerobic exercise stimulates the release of endorphins, which can act as natural pain relievers and mood lifters. Research suggests that regular physical activity may help reduce the intensity of menstrual cramps over time. The type and intensity of exercise should be guided by how you feel — some people prefer lighter activity on heavier flow days — but there is no medical basis for a blanket restriction. As with other lifestyle-related misconceptions, the evidence tends to favor flexibility over rigid rules, a theme explored in our piece on eating pattern myths that refuse to die.