This Week in Sex is a weekly summary of news and research related to sexual behavior, sexuality education, contraception, STIs, and more.

Period Tracker Blamed for 37 Unintended Pregnancies

Natural Cycles, a period tracking app that made news last year when it became the first app to be certified as a birth control method in Europe, is back in the news this week after a Swedish hospital reported 37 unintended pregnancies among its users. The hospital has reported the pregnancies to the Swedish equivalent of the FDA and asked for a review of the app.

Users pay a fee (equivalent to about $7-$10 per month) and get the app and a thermometer. They provide information about their menstrual cycles to the app and then enter their temperature each day. The app then uses an algorithm to determine if the user is fertile that day. A red sign means fertile days and indicates they should avoid sex or use another form of contraception.

This is a technology-based version of one of the oldest birth control methods—the rhythm method, which is also called natural family planning or fertility awareness methods. These have always been based on the understanding that there are only a few days a month in which a person can get pregnant. An egg is only viable for a short time after ovulation, and sperm can only live in a woman’s reproductive tract for about five days. If you can pinpoint this window and avoid unprotected sex during it, you can avoid pregnancy.

But that can be a big “if,” especially for women who have irregular cycles or keep a less-than-perfect record of their periods.

Overall, fertility awareness methods have a 24 percent failure rate under typical use, meaning that of 100 couples who use this as their primary birth control method, 24 will experience an unintended pregnancy within the first year.

Given that the failure rate for an intrauterine device (IUD) is less than 1 percent and the failure rate for the pill is 9 percent, this is pretty high.

Natural Cycles claimed it changes all of that with the information it collects and its unique algorithm. In fact, one study shows the app to have a 7 percent failure rate for typical use, which is better than the pill. The study also found that most of the failures occurred when couples ignored the app and had unprotected sex on fertile days.

The company says it’s been in touch with the agency, but argues that the numbers are not surprising because the app is not 100 percent effective. The more users they add (there are now reportedly 700,000 worldwide), the more failures there will be.

While this is true, one of the most important things to consider when choosing a contraceptive method is how easy (or hard) it is to do it correctly because—whether we’re talking about the pill, a condom, or an app—user error is the most common cause of failure. The pill won’t work if you skip three days, a condom that stays in the drawer beside the bed during sex is useless, and an app can’t be effective if you disregard its advice.

Smartphones may make our lives easier in many ways, but turning them into a contraceptive method takes daily effort and commitment.

Your Dentist May Start Asking About Your Sex Life 

Conversations with the dentist are always awkward. You’re in a chair, reclined all the way back, while your dentist’s face is looming over yours, half-covered by a mask. Half the time, they don’t start talking until your mouth is full of cotton, tools, and that strawlike thing that’s supposed to suck out the saliva but ends up vacuuming up your gums as you try to answer questions.

Now, a new study in the Journal of the American Dental Association may make things even more awkward, as dentists are being encouraged to screen for oral cancers caused by HPV—which means they could start asking you about your oral sex practices.

In the last installment of “This Week in Sex,” we reported on a retrospective study that found HPV-related cancers of the head and neck rose 2.5 percent per year between 2000 and 2012. The researchers who conducted that study believed that a rise in oral sex was partially responsible for the increase.

According to the Centers for Disease Control and Prevention (CDC), HPV is now thought to cause about 70 percent of oropharyngeal cancers, which includes conditions affecting the tongue, tonsils, and throat. So dentists can be a key to early detection of these cancers.

For the current study in the ADA’s journal, researchers conducted four focus groups with 33 dentists to determine how they were screening for cancer, what they knew about HPV, and what they discussed with their patients. The researchers found that most (though not all) dentists were aware of the role HPV played in oral cancers. But while dentists screened for visible signs of these cancers, they did not ask patients about their risk factors, such as multiple oral sex partners. Most dentists said they worried it would seem like they were passing judgment on their patient’s sex lives.

Ellen Daley, a professor at the University of South Florida and an author of the study, said in a statement: “Given the alarming increase of HPV-attributable oropharyngeal cancers, dentists and dental hygienists may be key agents for promoting HPV prevention. However, there’s a serious need for better training and education in the dental community.” The study recommends that dentists use their visits, in part, to educate patients about the risk of oral cancers, prevention methods (such as using a condom or dental dam for oral sex), and self-screening methods.

Of course, all of this can be done without asking a patient any specifics about their own sex life. But doing so could help the dentist know which patients are most at risk so they could screen more carefully.

So, get ready to say “oral sex” with a mouth full of dental tools.

Ikea Ad Is A High-Tech Pregnancy Test (With a Coupon!)

While we often line pets’ cages or litter boxes with old magazines and newspapers, few of us would ever think to pee on them ourselves. But that’s just what an Ikea ad in a Swedish magazine asked women to do. The ad was for one of Ikea’s low-cost cribs but doubled as a pregnancy test of sorts. If a pregnant woman peed in the box at the bottom of the page, red lettering would be revealed telling her that the crib was on sale.

The ad got a lot of attention on the internet last week for its unique—if slightly gross—gimmick. But, as we learn more, it turns out it’s much more than a joke. It was the impetus behind new technology that could have future uses beyond pregnancy testing.

Because the goal was to reveal a number of words, the test box in the ad could not rely on the same technology used in standard pregnancy test strips which only have to reveal a thin pink stripe. Jonas Hansson, product manager for Mercene Labs in Stockholm, which created the technology behind the ad, explained to the Verge, “When we tested materials similar to the ones in normal pregnancy tests, the wait until the text appears was almost an hour, and still very difficult to read.”

Ultimately, Mercene took a layered approach to the design. The urine dissolves red ink made of tiny particles infused with antibodies that attach themselves to hCG, a hormone found in the urine of pregnant women. Underneath that is a paperlike layer also infused with those antibodies, so that when the urine dissolves the ink, the ink sticks to the magazine pages revealing the message. These layers were sandwiched between two additional layers of a flexible substance that substituted for the hard plastic of a pregnancy test and allowed the magazine to feel like a magazine—and also not get soaked through or ripped when it gets peed on.

Hansson is working on a way to combine these layers into one synthetic paper and believes that this innovation could lead to advances in tests for harder-to-detect diseases.