Kent Hernandez/Fusion

By now you've probably heard about the YouTube star with two vaginas. But if you're like us, her story left you with questions. Such as—why? And how?

Yes, model Cassandra Bankson, famous for her makeup tutorials, revealed in a video to her subscribers that she is "twice the woman" after finding out she has two vaginas and two uteruses, due to a very rare condition known as uterus didelphys. Although the 22-year-old released the video in 2014, it didn't go viral until last week.

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So what does having "two vaginas" really mean? We did the research behind the anatomical science so you don't have to. Here's what we learned.

The condition

Bankson was diagnosed with uterus didelphys, a rare condition which only affects about 1 in 2,000 women worldwide. Doctors aren't sure why it occurs, but they do know how.

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During the embryonic stage of human development, females have two tubes (uterine horn) which fuse together to create one uterus. In women with uterus didelphys, this fusing never occurs, and the tubes develop separately—resulting in two uteruses. This can also mean having two vaginal openings and two cervixes, as in Bankson's case. Here's what that looks like:

Kent Hernandez/Fusion

Difficult to diagnose

Bankson says she always experienced brutal menstrual periods (makes sense in retrospect, given that she has two uteruses), but doctors didn't diagnose her until her twenties.

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The challenge in diagnosing the condition is that women with uterus didelphys may look "normal" on the outside—as in, their labia, vulva, vaginal opening, and clitoris (what we colloquially think of as the "vagina")—appear fine. Doctors have to look inside, using an ultrasound or MRI, to spot the issue. Women are often in the dark about their condition until they go to the doctor for some other problem (or, say, pregnancy).

Bankson, for example, went to the doctor complaining of back pain—only then did doctors discover that she had only one kidney and an extra uterus.

Is it dangerous to have a spare uterus? 

Several complications can arise from having uterus didelphys. First, as Bankson describes in her video, menstrual cycles can be unpredictable (she bleeds multiple times in a month). Second, pregnancy can be complicated for some (but not all), as women with the condition may be more prone to infertility, miscarriage, and premature birth than the general population. One reason? Both uteruses take up about the same space as one, so they tend to be smaller.

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While extremely rare, some women with the condition have grown babies in both uteruses at the same time. A woman in Florida gave birth to fraternal twins in 2011, one from each uterus. That same year, a woman in India also gave birth to twins from each uterus. And in 2014 a British woman gave birth to triplets, which meant an egg became fertilized in each of her uteruses, and one of those grew into twins. Three healthy baby girls were born.

Women with uterus didelphys often deliver via cesarian section, as all of the women above did.

What about sex? 

Not all women with uterus didelphys have two vaginas like Bankson, but for roughly 75 percent of women who do, those two vaginas are separated by a membrane called the vaginal septum. While the exterior opening appears "normal" on the outside (as in, there's one vaginal opening), there are two roads to take inside.

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The septum can make sex with a man a little, well, different for women with the condition. In some cases one vagina is larger than the other, and that's the one where the magic happens (i.e. the intercourse). In other cases one vagina might be blocked entirely, so the unblocked vagina would be used for intercourse.

Of course, some women have had sex in both—such as British woman Hazel Jones, who says she lost her virginity twice. #themoreyouknow

Taryn Hillin is Fusion's love and sex writer, with a large focus on the science of relationships. She also loves dogs, Bourbon barrel-aged beers and popcorn — not necessarily in that order.