We all know the basic concept of birth control. The purpose: Lower your risk of pregnancy by as much as humanly possible.

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Of course, no form of contraception is foolproof. But if you put the condom on properly (and choose the right one), take your pill regularly, and generally use birth control correctly, your chances of getting knocked up are indeed significantly lower.

But not using any barrier (literal or hormonal) and just trusting he'll pull out before any of his swimmers have made their way out and upstream? Well, there’s a reason they call it “pull and pray.”

Yet a shocking number of women are relying on what is the contraceptive equivilant of keeping your fingers crossed. A new survey from Glow, a menstrual cycle tracking app, found that 18 percent of women use the withdrawal method as their primary form of birth control.

Other research suggests the number may be even higher: A 2013 study from Duke found that 31 percent of women have used pulling out as their primary form of contraception at least once, while the CDC estimates that 60 percent of women have done so. And that same Glow survey found that pulling out was the third most popular form of birth control—more than an IUD!

Is It Legit?

“People do think of this as being contraception—but it’s not,” says Lauren F. Streicher, M.D., clinical associate professor of obstetrics and gynecology at Northwestern University and author of Sex Rx: Hormones, Health, and Your Best Sex Ever. Contraception, by definition, is a method used to prevent pregnancy, but pulling out has such a high failure rate, you can’t even really consider it a viable option, she argues.

But there are some perks: The pull-out method is free of hormones (strike one against the pill for many) and always available, no drugstore run required. Participants of the Glow survey said their top reasons for relying on it is that it feels the best and is the easiest contraception to use. And spermine, the compound found in sperm, is actually pretty good for your skin: It's believed to smooth out wrinkles and prevent acne.

But would you rather pay the price of a condom and a nice face cream or that of an unwanted pregnancy or a lifelong STI?

What the Stats Say

It's called "pull and pray" for a reason.

According to Planned Parenthood, among couples who pull out perfectly every time (read: before any semen comes out), only 4 percent of those women will become pregnant over the course of one year. Not too bad, right?

That’s in a perfect world, though. There’s another kind of failure rate, called the “actual” rate, that takes into account user error (in other words: not pulling out in time). Among couples who don’t time it perfectly, the actual failure rate for withdrawal is estimated to be around 27 percent over the course of one year.

Condoms, meanwhile, have an actual failure rate of 18 percent, according to the CDC. Compare those numbers side by side and pulling out doesn’t seem that far off from rubbers. In fact, a 2014 study found that withdrawal is "about as effective as condoms" at preventing pregnancy.

But consider this: Typically a condom fails because guys don’t put it on until after intercourse starts or don’t put it on correctly, Streicher says. While you and your guy can’t control things like the condom breaking, most responsible adults can eliminate those two other reasons right away, making your personal actual failure rate much lower by using a condom than pulling out.

The Real Problem With Pulling Out

When you compare pulling out to the pill (only a 6 percent failure rate) or an IUD (less than a 1 percent failure rate), it seems crazy to take such a chance just to have the pleasure of sex without a condom. “Withdrawal is at the bottom of the barrel when it comes to methods of not getting pregnant,” Streicher adds.

The failure rate is so high for two reasons: One, most people just don’t pull out fast enough, she explains. (It takes only one little swimmer, after all.) But even before a guy finishes, he typically releases pre-ejaculate—that clear fluid at the tip of the penis during an erection. When British researchers tested this stuff, one third of pre-ejaculate contained live sperm. Sperm content of pre-ejaculatory fluid. Killick, S., et al. Hum Fertil (Camb). 2011 Mar; 14(1): 48–52. “The idea that anyone can pull out fast enough to prevent a pregancy is just not true, making withdrawal not an appropriate form of contraception,” Streicher emphasizes.

(Too late? As Greatist expert Alyssa Dweck, M.D., points out, you may want to consider an emergency contraception pill, i.e. Plan B, if you've used the pull-out method as a last resort, especially if you're mid-cycle and ovulatory.)

But pregnancy isn’t the only problem. “Withdrawal is in no way going to protect you from STIs—period,” Streicher explains. You’re exposing yourself both to those transferred from skin-to-skin contact, like herpes, as well as those spread through the semen, like gonorrhea and chlamydia. (It's imperative to get tested regularly if you use the pull-out method.)

The other risk? Having a general shitty sexual experience, Streicher says. “When you’re constantly worried about pulling out in time—or if the guy will pull out in time—that doesn’t make for satisfying sex,” she offers. And to top it all off, you have the post-coitus stress of not being 100 percent sure no sperm escaped or if you’ve exposed yourself to an STI.

The Takeaway

If it’s so risky, why are so many people relying on pull-and-pray to keep them baby-free? In addition to theoretical ease of use and feeling good, “it’s a combination of someone not planning well—a lot of people pull out as a last resort if they weren’t planning on having sex but have no other contraception available—and wishful thinking that they’re going to be able to get away with it,” Streicher says.

However, “while it may not be the most reliable method for all couples, I wouldn't want to discourage people from using it as opposed to using nothing at all,” says Jessica O'Reilly, a Greatist expert and sexologist. Plus, as men age and become more experienced, they become more in tune with their sexual response cycle and may pull out with greater accuracy before ejaculating.

Still, it's not worth relying on the old got-away-with-it-before reasoning. “That’s playing with fire,” Streicher adds. “If someone is doing pull-and-pray, they have to be fine with the consequences of getting pregnant. If an unplanned pregnancy would be catastrophic, then you have to get a more reliable method of birth control—plain and simple.”

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