Period syncing is also known as “menstrual synchrony” and “the McClintock effect.” It's based on the theory that when you come in physical contact with another person who menstruates, your pheromones influence each other so that eventually, your monthly cycles line up.

Is it true that women's periods sync?

Given that menstruation can last 5 days, overlapping periods are a common occurrence. That women synchronize to each other, however, is a myth."

What does it mean when your period syncs with someone?

If you've ever lived with multiple people who have periods, you've probably experienced period syncing. Period syncing is the idea that when women live in close proximity to each other or spend a lot of time together, the timing of their monthly periods will start to "sync up" or align.