The public's collective knowledge of periods is rife with misinformation — for example, no, the full moon will not throw your cycle out of whack. Another popular period myth is the idea that the cycles of women who spend a lot of time together can sync. The "alpha uterus" myth is at the heart of this idea: One uterus that possesses such immense hormonal power that it pulls all nearby uteruses (uteri?) into its orbit, causing the women who own these uteruses to menstruate at the same time. Related: Exercise & Your Menstrual Cycle: What Your Period Means For Your Workout Schedule The truth: We have just one observational study from 1971 to thank for the syncing-periods myth, which should already give you an idea of the shaky science behind the "alpha uterus." Several other theories — involving potent pheromones and fertility — have been posed as to what could make a woman's uterus more, er, influential, but Rebecca Nelken, MD, tells Shape most of these are far from viable.
Related: The Best Foods To Eat When You're On Your Period On top of that, although it's kind of cool when you realize you share a period week with your roommate (you suddenly have a built-in PIC — Partner In Cramping), Dr. Nelken says there's no reason, from an evolutionary perspective, why women would need to cycle at the same time. "It's hard to imagine the survival advantage that would be conferred by this," Dr. Nelken says. "I can't think of a reproductive advantage either."
Click through to Shape for more on period myths and staying healthy during that time of the month. (Shape) Related: How Much Pelvic Pain Is Normal For Menstrual Cramps?