We've all heard the rumors: Someone got an STD from sharing underwear, or from swimming in a pool, or simply sitting on a toilet seat. But can you really get an STD from going about everyday life? Disease-transferring vectors like these aren't always covered in health class, so in an effort to discover the truth, we trawled for some of the most fringe queries on the Web and ran them by a handful of experts.
We were hardly the first to ask: People have long been preoccupied with unusual ways to contract STDs. "A few hundred years ago, humans were beginning to recognize the whole notion that some infections are transmitted sexually, and there were always stories of people who had gotten infected in which sexual explanation didn't fit well," says H. Hunter Handsfield, professor emeritus of medicine at the University of Washington and a spokesperson for the American Sexual Health Association. These stories were mostly invented to save face—it was easier, for instance, for a woman to explain that she contracted chlamydia from a toilet seat instead of admitting that her husband was cheating on her and lying about it.
Doctors also may have been at least partially to blame for the spread of some of this misinformation—in the 1800s in Europe, in an effort to destigmatize syphilis (which had ravaged the population since the late 1400s), doctors spread the rumor that you could get the disease from drinking fountains and communion cups, says Basil Donovan, a professor of sexual health program at the Kirby Institute for infection and immunity in society at the University of New South Wales in Sydney, Australia. (It didn't work to reduce the stigma.)
Today, the landscape is a bit different. Most people have multiple sexual partners before settling into a monogamous relationship, and that can make it harder to pinpoint when and how you caught an STD. "Now fewer people have had only one partner. So it's easier to say these are sneaky diseases that can pop up [long after a person initially contracts them]," Handsfield says.
The easiest way to get an STD is, of course, having sexual contact with an infected person. "STI bacteria and viruses evolved with humans in a way that requires especially large doses of the organism to come into contact with susceptible tissues. Those tissues not so easily accessible—that's why they're sexually transmitted to begin with," Handsfield says.
Still, there is a remote possibility of contracting sexually transmitted infections in nontraditional ways. A couple caveats before we get to the list: First, it's important to note that there's a difference between infections that are only transmitted sexually, and those for which sex is one of several vectors. This list includes infections that you probably categorize as STDs, but also includes some that can be passed on in other ways. Second, the terms STI and STD are used here interchangeably. Here's a look at a few of the most common ways people think you can catch an STD without having sex—and what the odds of that happening really are.
Fingering and hand jobs: Because the hands are dry and don't have mucosal membranes, there aren't many infections that can be transmitted through contact. But some hardy microbes do make it through. One is trichomoniasis (trich for short), a very common STD caused by a single-celled parasite. "Trich is a ravenous bug—just being in the neighborhood puts you at risk," Donovan says. But for an infection to occur, the infected person would have had to touch their own genitals, then use that same hand to touch their partner's genitals.
Anal fingering is also a risk factor for HPV (anal warts), Donovan says. Anal warts are common among homosexual men at least in part because HPV, too, can travel from skin-to-skin contact alone, including on the fingers. The best way to prevent contracting the condition is to get the HPV vaccine, Donovan says.
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Sharing lipstick, a drinking glass, or a cigarette: If you're concerned that you've swapped spit with someone who has an STD, you can probably rest easy. Saliva itself has antiviral properties, Handsfield notes, and you probably wouldn't be exposing yourself to high enough quantities of microbes to put yourself at risk. Even when it comes to oral herpes, Handsfield says you're likely in the clear. "With emphasis on 'theoretically,' maybe [transmission] could happen," he says. "But it is exceedingly unlikely, maybe no risk at all. If mentioned at all, the main point should be 'don't worry about it.'"
Sharing a razor: On its website, the Centers for Disease Control and Prevention (CDC) warns people living with HIV not to share razors or toothbrushes or any other "personal items that may be contaminated with infected blood." While that's generally advice worth following—for the sake of good hygiene if nothing else—the odds of getting an HIV infection from a used razor are actually pretty miniscule. "I am unaware of any reported cases of proved HIV transmission because of shared razors," Handsfield says, noting that the infected person and the non-infected person would have to use the razor within a few minutes of one another (and, presumably, cut the skin a bit) while the blood is still wet.
Insects: If you've been following the news lately, you probably already know that Zika virus can be transmitted sexually in addition to its primary vector: mosquitoes. But you shouldn't be too worried about this—Zika is rare in most parts of the world (and even rarer to transmit it sexually), Donovan points out, so it makes sense to be more concerned about diseases that are more common. Plus, if you do somehow get Zika (provided that you aren't pregnant), the symptoms are usually mild.
Lab-based experiments have also shown that houseflies can transmit the bacteria that cause chlamydia—which can affect the eyes as well as the genitals. For that to happen, however, would require the fly to land on an infected person's eye and then the recipient's eye within a relatively short timeframe. Theoretically possible? Sure, but we're not betting on it.
Sex toys and dolls: It's possible to get an STD from someone else if you're using a sex toy that was passed off shortly after someone else used it. "If a sex toy had been immediately used and still had wet secretions [on it], transmission could happen. But the notion that one that had been previously used and had been cleaned and is now dry [could transmit an infection] is nonsense," Handsfield says. You might think most people wouldn't need to be told to at least wipe down someone else's sex toy before using it themselves, but there is at least one example—in a 1993 case study—of a sailor who contracted gonorrhea after using an inflatable doll shortly after another member of the crew had used it.
Wet towels: If you ever hear a friend claim they know someone who got an STD from a damp towel, they're probably wrong. It's never been proven that wet towels can transmit the microbes that can cause STDs. But it's theoretically possible that the warm, damp environment could allow some of the hardier bugs to survive outside the body. Possible candidates may include trich and molluscum contagiosum, a viral infection most often passed between young kids who constantly touch their mouths, but can also be transmitted sexually. But for a disease to be transmitted this way, "you'd have to put it in the right place," Donovan says.
Toilet Seats/Tanning Beds: It's mostly an urban myth that you can get pregnant, or contract an STD, from a toilet seat. But it's happened, specifically to an eight-year-old girl who caught gonorrhea after cleaning a toilet seat then touching her genitals, according to a 2004 case study. "Gonorrhea cannot penetrate intact skin—it has to come into contact with a mucous membrane," Donovan says. "Most adults would wash their hands after touching a toilet seat, certainly before they touch their genitalia. Eight-year olds usually don't." Studies show that toilet seats host a range of nasty microbes that can cause conditions from Ebola to staph infections. So if you need another reminder to wash your hands after you use the toilet, consider this it.
Some experts have also predicted that it's possible to contract HPV from a tanning bed. In theory, this could happen if an infected person uses the bed without wearing an undergarment, and the bed is not properly cleaned before the next person uses it. The microbes would also have to survive the UV light and dry, unwelcoming environment on the bed. Again, not super likely. As Donovan says, "Anything is possible. But I've never seen it or heard of it."
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