This Report Shows How Periods Are Still A Mystery

Millions of people in the United States are affected by endometriosis, polycystic ovary syndrome, and all kinds of other menstrual problems each year, yet we're still stuck wondering the same thing: What causes menstrual disorders? Despite advances in modern medicine that wouldn't seem out of place on the set of Star Trek, we're not much closer to understanding periods now than we were decades ago. In fact, according to a report by researchers at the University of Edinburgh, the science behind everyone's least favorite monthly visitor is still largely a mystery.

In the report, Dr. Hilary Critchley and researcher Jacqueline Maybin reviewed more than 40 years of research on the subject of menstruation, only to come up with more questions than answers. Why do some women bleed more than others? Why is heavy flow sometimes an indicator of a larger problem like endometriosis — but only sometimes? How does the uterine lining rebuild itself so quickly, despite being shed month after month until menopause? Unfortunately, Critchley explained to Live Science in an article on the Huffington Post that the research looking into these questions, which most would say are vitally important to understanding the female body, simply doesn't exist.

"[Menstruation is] so crucial for the reproduction of our species. But it's not a popular topic to study," Critchley told Live Science. As for why menstrual research is so sparse, you have three guesses, and the first two don't count. Even in so-called progressive countries, the stigma surrounding periods is so deeply entrenched that many women are embarrassed to admit they have one at all, let alone that it can be debilitating.

But Critchely and Mabyin's paper isn't interested in the social factors behind this lack of information. Rather, the report focuses on the answers we do have, as well as the further questions they raise. Let's take a look at what researchers know about menstruation so far — and what we still have yet to discover.

1. Some People Bleed Much More Than Others

If you've ever compared notes with a friend, you've probably realized that some people have much heavier periods. My sister can go to sleep with just a tampon, for instance, while I have to prepare for battle with a super tampon and diaper-like pad. Even then, I'll probably still bleed everywhere because that's just how my uterus lives its life. According to Critchley, researchers are well aware of the differences in flow; in fact, heavy menstrual bleeding is actually considered a disorder if someone bleeds more than 2.7 ounces per period. However, some women have much, much heavier flows than that, which can quickly disrupt their lives.

So what causes this difference? Who knows!

2. Inflammation Causes The Uterine Lining To Shed

It's well known that the hormone progesterone is responsible for starting menstruation. What many people don't realize, though, is that there's another step before your uterus starts to shed the lining: Inflammation, which is caused by the drop in progesterone. Although the mechanism isn't understood, researchers believe that inflammation causes the breakdown of the uterine lining. Once they figure out how this happens, Critchley told Live Science that it could give scientists insight into why some women bleed more.

3. The Uterus Rebuilds Itself Incredibly Fast

Despite shedding its lining every month, the uterus manages to rebuild its walls entirely in the early stages of the menstrual cycle. According to Critchley, the uterus goes from looking like a "wound" during your period to being a "lovely, smooth, velvety surface" in just 10 days. So how does this happen? Scientists aren't sure, although some believe it could be the uterine wall dividing itself over and over again. Then again, the cells could come from elsewhere in the body. Without further research, it's hard to tell.

4. The Uterus Doesn't Scar

Despite everything the uterus puts itself through, it manages to bounce back time and time again without scarring. As Critchley pointed out to Live Science, this isn't just important for understanding menstruation: The liver is also capable of repairing itself without damage, but over time, scars develop on the organ and cause liver problems. If we can figure out how the uterus manages to repair itself so often and not scar, we might be able to use that knowledge with other organs. Besides, isn't it about time we spent as much time understanding women's bodies as we do men's?

Images: Andrew Zaeh for Bustle; Giphy (5)