The spread of Covid-19 has turned us into a nation of hand-washing obsessives, citizens who vigorously interlace our fingers and circle-scrub our thumbs with an exacting, anxiety-fueled intensity. But it’s not over when you flip off the faucet: Drying your hands matters too, because damp skin provides a hospitable environment for microorganisms and, as a result, might increase the likelihood that you’ll pass on pathogens.

So now, as we confront what could be a society-altering disease outbreak, it seems worth taking a hard look at the widely reviled yet seemingly ubiquitous electric hand dryer. Are they as hygienic as paper towels, as their manufacturers claim?

The earliest pitches for hand dryers played up their supposed ability when it comes to “preventing the spread of contagious disease,” as a 1924 newspaper ad for the Airdry Electric Towel put it. More recently, Dyson, whose Airblade hand dryer promises to “scrape water from hands like a windshield wiper,” has bragged that its HEPA air filter captures particles as tiny as .3 microns in diameter, much like the N95 face masks that are now selling for AirPod Pro–equivalent prices on Amazon.

But the quality of the intake filter doesn’t address whether blowing air at high speeds is a smart idea given that it may be sending droplets and particles from your just-washed hands flying rapidly every which way. When you dig into the science on hand dryers, you’ll come across reason to be concerned. A study published in 1989 found that gentler, old-style hand dryers blew bacteria over a three-foot radius and onto the user’s clothes, which considering the era was probably an acid-washed jean jacket.

A 2018 study produced even more troubling results, finding that “potential pathogens and spores” could be “dispersed throughout buildings and deposited on hands by hand dryers.” It tested conventional hot-air models with and without filters and determined that the filters “most likely reduce the number of potentially pathogenic bacteria with the potential to colonize hands but do not eliminate the risk entirely.” A 2015 study found that super-aggro hand-dryers like the ones made by Dyson, which use higher-speed jets of air at room temperature, "produced significantly greater aerosolization of virus on the hands" than the traditional kind. Paper towels, meanwhile, were found to cause about the same amount of viral spread as hot-air models.

A 2012 analysis of 12 studies over four decades published in Mayo Clinic Proceedings concluded that “[f]rom a hygiene viewpoint, paper towels are superior to electric air dryers” and that they should be used in “locations in which hygiene is paramount, such as hospitals and clinics.” Though it could be argued that hygiene should be paramount in the restroom of, say, your neighborhood Panera Bread, too. The analysis did find that dryers like Dyson’s “led to much less bacterial transfer than hot air dryers.”

So does that tell us anything about whether hand dryers could spread a virus like the one that causes Covid-19? I called Peter Setlow, a biochemist at the University of Connecticut and one of the authors of that 2018 study. Setlow is a “spore guy” not an infectious disease expert, but he nonetheless came away from that research with a deep and abiding distrust of hand dryers regardless of the model. “Sorry, hand-dryer industry,” he told me. “My personal opinion is that they shouldn’t be used.”

There’s been understandable blowback from the hand-dryer industry, which questions the methodology of some of this research and notes that certain studies pegging hand dryers as disease vectors—including the one cited above, from 2015—were carried out by researchers who had worked as consultants for paper-towel manufacturers. This is true in some, though not all, cases. Dyson got in on the game by funding a study, published last April, that found—surprise!—hands dried with the company’s own Airblade harbored fewer bacteria than those dried with paper towels.

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There’s reason to be skeptical of last year’s paper. In the study, subjects “slowly” moved their hands in and out of the machine for a full minute, something no normal human is ever going to do. Besides, Dyson says elsewhere that the model dries hands satisfactorily in a mere 12 seconds, so which is it? More importantly, that study only looked at the bacteria left behind on hands post-drying, not whether particles might have been blown onto your clothes.