Plenty of microbes — bacteria and viruses alike — use the close contact of a sexual encounter to leap from one host to the next. As a result, health experts wisely counsel protection to avoid the health issues and infertility these infections can bring. While everyone should certainly heed those warnings and practice safe sexual contact, biologists also know that some sexually transmitted microbes can provide benefits, reports Niki Wilson for BBC.

Take the GB virus C (GBC-C) for example, which often shows up with other much more dangerous viruses like HIV. But when it comes along for the ride, studies show that GBV-C actually reduces the mortality rate of HIV patients by 59 percent, Wilson reports. It’s also been shown to boost the chance of surviving an infection with Ebola.

Wilson writes:

Extraordinary discoveries such as this should make us wonder what else we are missing, says Betsy Foxman, of the University of Michigan, US. In the past we’ve characterized sexually transmitted microbes as bad, she says. The preventative measures we’ve taken to protect against them may mean that we now lack some that are potentially beneficial.

However, figuring out how to protect against the bad while letting in the good may be a bit of a challenge. Foxman points to a need for more targeted antibiotics that kill only harmful bugs, and let the harmless (or beneficial) ones keep on keeping on. Or perhaps there’s a way to inoculate people with the good bugs after they take a course of antibiotics.

Beneficial sexually transmitted microbes aren’t just found in humans of course. There are a few microbes that pass between mating aphids that can make the infected insects more resistant to parasitoids or better able to tolerate heat. Mosquitos carry bacteria in their gut that can pass as a nutritional coating on the surface of developing eggs, ready to provide a snack to just-hatched larvae. Promiscuous female birds and lizards may actually gain protective microbes — in the form of healthy, diverse microbial communities or in the form of viruses that kill harmful bacteria, Wilson writes.

All these findings emphasize once again the many questions scientists have about the microbiome, or the bacteria and viruses that live in and around humans. The fact that sexually transmitted microbes have a complicated story as well doesn’t seem as surprising in that light. But until scientists really get the story straight, keep in mind that many STIs are harmful. Sex doesn’t automatically spell certain death (as it does with the male dark fishing spider) but it's worth being safe when you have it.