A scientist tested the air from a hand dryer and the results are wild. But there's a catch.

Even under the best of circumstances, public restrooms are pretty gross. Most of us like to spend as little time as possible in there, touching as few surfaces as we can manage. Then, we promptly and thoroughly wash our hands so we can get the heck out of there.

But first, we have to dry our hands. Many, if not most, public restrooms offer air hand dryers of all different makes and models. They cut back on paper waste and, unlike paper towels, they never run out and leave patrons in a lurch. But are they actually hygienic?

In 2024 a scientist from the UK, Ruth MacLaren, went viral after conducting a simple bacteria test on a public restroom hand dryer.

MacLaren is the founder of Devon Science, an organization that helps kids get involved with STEM through science parties, interactive experiments, and educational programming.

"Urghh, don't use a hand dryer," the caption read to her original video posted on TikTok. In the experiment, she placed an agar plate (a sterile petri dish filled with a jelly-like substance that collects bacteria and other particles) under the dryer as it blew air. As a control, she wafted another agar plate around in the air and let both plates sit overnight.

The next day, the results definitely...blew her away.

The petri dish that was exposed to the hand dryer grew dozens of visible clusters of bacteria, including many different varieties. The sample of regular air, on the other hand, grew nothing; indicating very little bacterial presence.

MacLaren's video racked up over 28 million views across social media and thousands of comments from icked-out viewers.

"This is also why we don’t use hand dryers in health settings , soap water and a disposable towel is best," one person wrote.

"I will never use one again," added another.

Several folks chimed in to add that they've never liked hand dryers, and not because of anything to do with hygiene. The incredible noise-level coming out of them has been well-documented as problematic for children or people with sensory issues.

"Me with my autism not using hand driers because the sound of them makes my brain go *stressed screeching*" a commenter wrote.

"I hate the blowers... they're loud, they're too hot, I just want paper towels & a recycling bin to put them in" said another.

To celebrate the roughly one-year anniversary of her massively viral hit, MacLaren revisited the same hand dryer and performed another test—but with a few tweaks that shed even more light on the problem.

This time she sampled the air from the bathroom (and not her workspace), and she also modified the test to see if the germs from the air blower were transferring to her hands after she had washed and dried them.

While the new sample of the bathroom air did show some bacteria, the growth had nothing on the hand dryer sample, which once again grew significant bacteria. Even more upsetting, MacLaren's before and after sampling of her hands showed quite a bit of bacteria even after washing and drying using the blower. Unfortunately, that's sort of the opposite of what we're all going for when we take the time to thoroughly wash our hands.

MacLaren is not the first or only person to discover the less-than-ideal cleanliness of air hand dryers.

While MacLaren explicitly caveats that her experiments are just casual quick-tests and not scientifically validated studies, scientific studies have in fact been performed in this area.

One study published in the Applied and Environment Microbiology Journal found that "many kinds of bacteria, including potential pathogens and spores, can be deposited on hands exposed to bathroom hand dryers and that spores could be dispersed throughout buildings and deposited on hands by hand dryers."

It's worth considering that there are many different kinds of hand dryers available in public restrooms. The one MacLaren tested in her videos is a little old-fashioned and likely not equipped with a very efficient filter. State-of-the-art hand dryers usually feature HEPA filters that are supposed to catch germs and viruses from the air so they're not re-distributed. But even more modern options, like the Dyson Airblade, have routinely failed bacterial tests.

It seems clear that old-fashioned paper towels are the more hygienic option. But, like a good scientist, MacLaren decided it was only fair to test those as well.

She was extremely surprised to learn that drying her hands with a paper towel still left quite a bit of bacteria on her hands. In fact, testing just a dry paper towel (with no contact to her exposed hands), unbelievably, showed substantial amounts of bacteria growth fresh out of the package.

The most effective test involved washing thoroughly, drying with a paper towel, and then using hand sanitizer. But, MacLaren warned, "That clearly works great ... but I'm killing my good friendly microbes as well."

"Will we ever be clean?!" one commenter lamented.

"Just wash your hands after drying them. easy," joked another.

All is lost not, however. In a series of follow-up videos, MacLaren makes it clear that she's not fear-mongering about germs. The bacteria found in her testing are generally not harmful to most people.

"All of you have been asking about the kinds of bacteria on these agar plates... They're just normal environmental microbes," she says. "A lot of them are bacteria you find on your skin. But for me it was the quantity of bacteria coming out of the machine that was a bit of a shocker."

Harvard Health confirms that in scientific studies, "the vast majority of the microbes that were detected do not cause disease in healthy people." Gross? Yes. Dangerous? Probably not.

Immunocompromised folks may want to take extra precautions, however.

In the end, the most optimal course of action most experts including MacLaren agree on is to wash your hands and dry with a paper towel. All the better if you have access to a clean cloth towel. But as the tests prove, it's nearly impossible to get all the bacteria off your skin. Even if you could, you might not want to. Excessive removal of oils, microbes, and bacteria on your skin (say, from too much hand sanitizer) can cause dry, itchy skin and can worsen skin conditions like eczema.

Maybe it's time to bring back the clever, if a little unsettling, rotating hand towel devices that used to be found in public restrooms:

For now, the best strategy is still the time-tested one: Get in and out of the public restroom as fast as possible.