Lately, sex researchers have noticed a troubling trend: After steadily climbing since the 1990s, condom use in America is falling—especially among young men.

Between 2002 and 2010, the percentage of teen guys who used a condom during their first sexual experience jumped from 71 percent to nearly 80 percent, according to research from the Centers for Disease Control and Prevention (CDC). But from 2011 to 2013, that figure dropped to 78 percent.

No, that doesn’t sound like much. But the drop-off seems to be steepening, says Debby Herbenick, Ph.D., a sexual health researcher at Indiana University.

One theory: Young guys misunderstand rubbers. “I see some of my own students coming in thinking condoms are only for birth control, which is crazy,” Herbenick says.

Part of the problem is marketing. While condoms were synonymous with fighting off HIV and disease in the 1990s and early 2000s, Herbenick says recent public health campaigns have emphasized pregnancy prevention.

At the same time, the use of “long-acting reversible contraception” methods, or LARCs, has increased among women, Herbenick says.

These birth control measures come in the form of arm implants and inter-uterine devices—and both are better than condoms at preventing pregnancy. According to the CDC, condoms are effective 82 percent of the time, while pills and LARCs are close to 99 percent effective when used correctly.

If you know your partner is protected, maybe you don’t see a need to follow suit, says Herbenick. But when it comes to sexually transmitted infections (STIs), condoms are the only way to protect yourself and your partner.

“If we had a way to test for it—which we don’t—40 to 60 percent of college-aged guys would test positive for HPV,” Herbenick says. Rates of chlamydia are also high, she says, but both STIs have no symptoms. “So guys don’t even realize they have them.”

HPV can trigger penile, head, and neck cancers later in life, Herbenick says. Meanwhile, chlamydia infections can mess with your internal plumbing in ways that could make it tough for you to have kids.

And then there’s the other culprit in the case of the disappearing condoms: “A lot of younger men learn about sex by watching porn, and you hardly ever see condoms worn,” Herbenick says.

It’s also common in porn—or so we’ve heard—for the guy to pull out and masturbate before letting loose onto his partner. Young men adopt this practice, Herbenick says, and mistakenly assume they don’t have to worry about unintended pregnancy since they withdraw before climax.

“Of course, your partner can still get pregnant even if you pull out,” she says.

It isn’t rocket science: The safest scenario for you and your partner is to combine the STI protection of a condom with the birth-control effectiveness of LARCs or the pill.

“I don’t expect guys to wear condoms forever,” says Herbenick. In long-term relationships, if both people are faithful and healthy, contraception is really the only concern, she says.

But if you have sex with multiple people, or you’re in the first few months of a new fling, you shouldn’t think twice about wrapping your willie.

Want to make safe sex hotter? A 2012 study in the Journal of Sexual Medicine found that sexual pleasure increased when the guys reported they were satisfied with how their condoms felt.

“I tell guys if they apply a little lubricant after they’ve put the condom on, that can also really improve the feel,” says Herbenick.