It’s commonly believed that womxn who live or spend a lot of time together eventually “sync” cycles, but does the science add up? (Spoiler alert, no). Many people still believe in the phenomenon because it can promote bonding and a sense of sisterhood. There’s nothing like the shared experience of menstruation to make you feel close to someone else, so even though you can't actually sync cycles with someone just by being around them a lot, we’re all in this together at the end of the day.

https://yourdaye.com/vitals/womens-health/is-it-possible-to-sync-periods