The menstrual cycle has been fascinating and baffling we humans since the beginning of time. Unlike any other fact of life, getting your period is at once a normal bodily function, a rite of passage, and historically, a fraught cultural event.There actually aren’t a ton of mentions of menstruation throughout recorded history, probably because men were the ones in charge of writing things down. But for centuries, teachings from various world religions, including Judaism, Islam, and Christianity, have said that menstruation is both physically and spiritually unclean, forcing menstruating people to be isolated. In fact, the Hebrew word for “menstruating woman,” niddah , also translates to “expelled.”Meanwhile, many cultures believed that menstrual blood is literally magic — the dark kind, mostly. For example, the ancient Roman scholar Pliny The Elder wrote that contact with period blood “turns new wine sour, crops touched by it become barren, grafts die, seed in gardens are dried up, the fruit of trees fall off...and a horrible smell fills the air; to taste it drives dogs mad and infects their bites with an incurable poison.” According to Cherokee teachings , menstrual blood was thought of as “a potent force possessing rare destructive capacity” that could be unleashed in sorcery rituals. It is considered so powerful a substance that the idea behind the isolation of menstruating women in Cherokee traditions is not cleanliness but safety.And this is just a sampling of what history tells us about the myths surrounding the actual bleeding part. What about premenstrual syndrome (PMS)? And ovulation?The point is, myths about the menstrual cycle are as essential to the human experience as the sunrise or the sunset. These myths have been around forever, and they continue today, albeit in less mystical forms. For example, many people still aren’t sure whether period sex can lead to pregnancy (it can) or even whether PMS is real or not (it is). The good news is that, unlike the intractable facts of the earth’s orbit, period myths are something we can actually change.Ahead, a guide to the real truth about your menstrual cycle, once and for all.