For years, researchers have been studying ways to prevent viral infections by strengthening immune defenses at the entry points of viruses into the body: the nose.

A study recently published in PNAS presents a similar, if lower-tech, idea. Coating the inside of the nose with the over-the-counter antibiotic ointment Neosporin seems to trigger an immune response that may help the body ward off respiratory viruses like those that cause COVID-19 and the flu, the study suggests.

The research raises the idea that Neosporin could serve as an “extra layer” of protection against respiratory illnesses, in addition to existing tools like vaccines and masks, says study co-author Akiko Iwasaki, an immunobiologist at the Yale School of Medicine and one of the leading experts in the U.S.

The study builds upon some of Iwasaki’s previous work—which has shown that similar antibiotics can trigger potentially protective immune changes in the body—but it’s still preliminary, she cautions. For the new study, her team had 12 people apply Neosporin inside their nostrils twice a day for a week, while another seven people used Vaseline for comparison. At several points during the study, the researchers swabbed the participants’ noses and ran PCR tests to see what was occurring inside.

They found that Neosporin—and specifically one of its active ingredients, the antibiotic neomycin sulfate—seems to stimulate receptors in the nose that “are fooled into thinking there’s a viral infection” and in turn create “a barrier that’s put up against any virus,” Iwasaki explains. In theory, she says, that means it could protect against a range of different infections.

Right now, though, that’s just a theory. For this study, Iwasaki’s team didn’t take the next step of testing whether that immune response actually prevents people from getting infected when they’re exposed to viruses—in part because it’s ethically questionable to intentionally expose people to pathogens for research. (They did, however, demonstrate that rodents whose noses were coated with neomycin were protected from the virus that causes COVID-19.)

On its website, the manufacturer notes that the product has not “been tested or formulated to prevent against COVID-19 or any other virus,” and also note that they do not advise putting the product inside the eyes, nose, or mouth.

Dr. James Crowe, who directs the Vanderbilt Vaccine Center and was not involved in the research, says the study is “intriguing,” but he’d need to see more human data before he gets excited. “I’m skeptical it would be strongly effective in people,” Crowe says. “If you have a modest effect on the virus, is that enough to really benefit you clinically?”

It is somewhat counterintuitive to think that an antibiotic, which kills bacteria, could do anything to protect people from viruses. It’s not that the antibiotic has a direct effect against viruses, Iwasaki explains. Instead, it seems that neomycin, when applied topically, provoke changes in the body that help it fight off viruses—essentially, triggering a natural antiviral effect.

So should you smear Neosporin in your nose ? Not so fast, says Dr. Benjamin Bleier, who specializes in nasal disorders at Massachusetts Eye and Ear and has studied intranasal therapies.

Bleier, who was not involved in the new study, calls the research “very well done,” but says there are questions that need to be answered before it hits “clinical prime time.” First, could the body develop tolerance or resistance to neomycin if the antibiotic were regularly used in this way? (Antibiotic resistance is a growing concern, and overuse is a contributor to the problem.) Second, could the average person apply neomycin deeply and thoroughly enough for meaningful protection? And finally, could this approach damage the delicate inner nose or have other side effects over time? (Even in the small study, one of the people who used intranasal Neosporin dropped out due to minor side effects, apparently related to a drug allergy.)

“It’s great science, but there’s still a long way to go before we should put it in our noses,” agrees Dr. Sean Liu, an infectious disease physician at New York’s Mount Sinai health system who was also not involved in the study.

Iwasaki agrees that more research is necessary. She says the next step is testing higher doses of neomycin, since Neosporin contains a fairly small amount that may not be enough to provide robust protection for humans. To gather more data, she says, researchers could track people going about their normal lives—except that some apply neomycin to their noses and some apply Vaseline—and see if one group gets sick less often than the other, though that would require a lot of time and people.

Despite the difficulties, Liu says there’s good reason for further study. Finding new uses for affordable, widely accessible medications is good for public health, and any progress toward neutralizing viruses is welcome. If the approach is proven to work, it could also be useful to have a tool that’s effective against a broad range of viruses and could potentially be paired with other drugs to strengthen its efficacy, Crowe adds.

Plus, Iwasaki says, additional disease-prevention tools could help people who are especially vulnerable to respiratory diseases—such as the elderly—and need additional protection to feel safe. If further research proves promising, Iwasaki says, she could imagine neomycin serving as an additional disease-fighting tool when people are in particularly germy places, like a crowded party or an airport.