Sometimes you have a sex question that's not just, you know, an idle passing thought. And in those times you need a real answer—one that's based on deep research and scientific rigor. In those times you need Hard Data. In America today, it's all about anal. According to Pornhub, US searches for anal sex increased 120 percent between 2009 and 2015. It's not just a highly sought-after porn genre, though—more and more Americans are giving it the old college try IRL, too. The latest data from the CDC show that 42 percent of men and 36 percent of women have tried anal at least once before, a significant increase compared to the 1990s, when just one-quarter of men and one-fifth of women had done it. As anal has increased in popularity, curiosity and concern about the potential long-term effects of being on the receiving end of it—or, as some call it, "bottoming"—have also spiked. I've seen this firsthand in my work as a sex educator, where questions on this topic have been on an upward trend, both in my classes and in my email inbox. The specifics of the questions have certainly varied, but most can be reduced to one thing: "Will anal sex mess up my butt?" If you search online for the answer to this question, you'll come across a lot of contradictory information. Some websites claim that anal is perfectly harmless, whereas others argue that it inevitably causes a host of health problems. Needless to say, this has generated a lot of confusion. Let's clear things up once and for all by taking a look at what science has to say about anal sex and anal health. After scouring the data and talking to the experts, here's what I discovered. There's a mountain of research looking at anal sex as a risk factor for STIs—something that I think most readers are probably already well aware of. As a result, I won't dwell on that here other than to offer a friendly reminder that if you're having anal sex, condoms and PrEP are fantastic ways of minimizing infection risk. By contrast, just a handful of studies have, ah, probed whether anal sex has any implications for anal functioning. What purports to be the very first study on this topic was published in 1993. In it, researchers compared the bowel habits and anal functioning of two groups of guys: 40 gay men who reported a history of receptive anal sex to 18 heterosexual men who claimed to have no experience with bottoming. As part of this study, researchers put balloons up these men's butts and filled them with water in order to measure their anal pressure. Because science. So what did they find? Receiving anal sex was associated with lower anal resting pressure (meaning the muscles down there weren't as tightly contracted), as well as reports of minor symptoms of fecal incontinence, such as feeling a greater sense of urgency when it comes to defecating. A subsequent 1997 study replicated the link between having a history of receptive anal sex and lower anal resting pressure; however, it failed to find a link with incontinence. The inconsistent findings about incontinence make it difficult to draw conclusions. We can't really say what the lower anal resting pressure results mean either, because the authors of the latter study argue that this lower pressure might just be a sign of greater comfort with anal stimulation—in other words, maybe guys who had bottomed before were just a little more relaxed while they were being probed. Oh, and keep in mind that both studies were based on very small samples and focused only on men. In an attempt to clear up the confusion and address these limitations, a new study on anal sex and incontinence was published earlier this year, in which over 4,000 American adults were surveyed. Researchers found that both women and men who had a history of receiving anal sex reported higher rates of incontinence than those who had never done so (9.9 percent vs. 7.4 percent for women and 11.6 percent vs. 5.3 percent for men). Although these results would seem to confirm that there is a link between receiving anal sex and experiencing bowel control issues, it is important to note that these data do not show cause and effect, and a quick glance at the stats reveals that the vast majority of those who were having anal sex were not incontinent. In other words, this suggests that if you're having anal sex, odds are very good that your butt is going to keep working just fine. Beyond incontinence, are there any other potential effects of anal sex on anal health? I've received several questions about whether anal sex can cause rectal prolapse, a condition in which the walls of the rectum fall out of position and start protruding outside of the body. However, it turns out that rectal prolapse is extremely rare and, aside from a few anecdotal reports, I had a really hard time finding any research suggesting that anal sex is likely to cause this. One exception was a 2015 article published in the Indian Journal of Applied Research entitled "Rectal Prolapse Due to Anal Sodomy!!!!!!" No joke—they used six exclamation points in their title. I don't know about you, but the extent to which I take a given journal article seriously is inversely proportional to the number of exclamation points in the title. This isn't to say that anal sex never causes rectal prolapse, though—it's just that if it does, it's probably a very uncommon occurrence given how widespread anal sex is and how rare reports of rectal prolapse are. The other main worry some people have about anal sex is the potential for physical trauma to the anus itself. Medical experts think microtears in the rectum are common during anal sex—just as vaginal microtears are common during vaginal intercourse; however, these tend to heal quickly and are unlikely to pose a significant health threat aside from increasing the risk of STI transmission. Significant physical trauma due to anal eroticism is rare, and most cases that have required medical attention have been attributed to activities like fisting. Thus, aside from those who are really pushing their body's limits, there isn't really any evidence that anal sex is likely to damage the anus. I spoke to sexual psychophysiologist and CEO of Liberos LLC Nicole Prause, who echoed these conclusions: "More common anal sex practices seem very unlikely to cause serious health issues." However, Prause went on to note that "research on obstetric injuries give us some idea that speed and force are the major issue in traumatic injuries. People should probably keep in mind how much the stimulator (penis, toy, fist, etc.) is going to stretch the anus and adjust the speed down accordingly for size. It would be especially risky to use a bigger stimulator with speed." In other words, the way most people have anal sex probably isn't going to cause problems; however, the extreme anal that you might see in certain kinds of porn—like double penetration—does have the potential for harm. As such, Prause cautions that "anal portrayed in films should really be thought of as fantasy-only and does not reflect how physiology actually works." Indeed, some porn actresses have gone public with reports of anal injuries they have sustained on set; however, we don't really know how common this is. It's likely that most performers keep injuries of this nature quiet either out of embarrassment or because it could potentially hurt their ability to get work in the future. In addition to suffering in silence, performers who are injured face a financial cost in that insurance and worker's comp don't cover sex injuries from porn shoots. The bottom (har) line: The available scientific evidence suggests that, for the vast majority of people having anal sex (porn stars notwithstanding), major injury, rectal prolapse, and bowel control issues seem to be highly unlikely outcomes. With all of that said, for those having anal sex, there are certain steps worth taking in order to keep your risks as low as possible. First and foremost, protect yourself from STIs (again, condoms and PrEP are great tools). Second, relax, take things slow, communicate very clearly, and use lots of lubrication (although Prause cautions that you might want to "avoid going too crazy with the lube" so as not to accidentally work up too much speed). And finally, recognize that taking anal to the extreme is risky, so think twice before you consider imitating those more adventurous porn scenes.