In the late 1960s, an undergraduate psychology student at Wellesley College named Martha McClintock noticed something interesting: Women who spent a majority of their time together tended to get their periods around the same time. She suspected that menstruating bodies could influence one another somehow, but it was just a hunch. So she asked 135 of her fellow students to keep track of their cycles. Three times that year, she quizzed them about their period start and which women they socialized with the most.
Initially, it seemed McClintock was right: Close-knit groups of friends tended to start their periods together. The phenomenon of menstrual synchrony was nicknamed the "McClintock effect," and her work was lauded as one of the first mainstream studies to demonstrate how one person's body chemistry can trigger responses in another's. But McClintock's results have been difficult to replicate; now, the scientific consensus is that cycles probably don't sync up — a claim that rings untrue to anyone who menstruates. My friends and I joke that we even seem to sync up digitally, thanks to constant contact via iMessage, Snapchat and Twitter.
The unresolved nature of McClintock's investigation, now almost 50 years old, underscores the unnerving amount of opacity that still surrounds women's health. Even today, it's difficult for women to get a sense of what's normal and what isn't. When my friends and I talk about our bodies, we compare feedback from physicians, all of which seems to be slightly different; we warn one another about conditions like uterine fibroids and share horror stories about different methods of contraception. There still seems to be a combination of prudishness and ignorance around the unique, and sometimes idiosyncratic, functions of the female body — which is shocking, considering half the world is born with one.
But in recent years, mobile technology has granted me and countless others the ability to collect an unprecedented amount of information about our habits and well-being. Our phones don't just keep us in touch with the world; they're also diaries, confessional booths, repositories for our deepest secrets. Which is why researchers are leaping at the chance to work with the oceans of data we are generating, hoping that within them might be the answers to questions medicine has overlooked or ignored.