When you use a hand dryer in a public bathroom, you probably feel good about the fact that it’s an environmentally-friendly alternative to paper towels, and it’s more hygienic to boot, right? When it comes to the second point, we have some bad news to share.
Researchers from the University of Connecticut conducted a study with a disturbing finding: Hand dryers can actually suck up microscopic particles, including human waste, and then spray them onto unsuspecting people drying their hands.
In fact, after 30 seconds under a hand dryer, a person collects approximately 18 to 60 colonies of bacteria. By way of comparison, a plate which sat in the bathroom for two minutes without the hand dryers on collected only one colony during that time.
Yikes! The study, published in February 2018 in the journal Applied and Environmental Biology, had researchers use plates to collect bacteria from hot-air hand dryers in men’s and women’s bathrooms at an academic health center.
And boy, did they collect it. As so many public bathrooms don’t have lids on their toilets, the bacteria inside them can become aerosolized — or made into mist — when flushed. The hand dryers then suck up the air and blow it back out onto your warm, damp hands.
To be fair, not all bacteria is necessarily bad; the human body is covered in bacteria, in fact, and most of them aren’t harmful. But the specific bacteria you’re likely to find in a bathroom is, well, yucky.
“It is reasonable to expect that the more bathroom air, especially if it is ‘unfiltered’ air, that is blown on a surface such as just-washed hands, the more bacteria will be deposited on hands,” Peter Setlow, a professor of molecular biology and biophysics at the University of Connecticut and an author on the study, told Allure.com.
Don’t freak out too much, though. One way to reduce the problem is to fit the hand dryers with HEPA (high-efficiency particulate air) filters.
Unfortunately, this is not the first time that hand dryers were shown to be less than squeaky clean. A 2016 study in the same journal found that jet air dryers spread 1,300 times more viral plaques than paper towels do. And due to the force of the air, the viruses can spread about 10 feet!
Back in January 2018, a woman named Nicole Ward’s Facebook post went viral after she showed what grew in a petri dish a few days after sitting in an enclosed hand dryer of a public bathroom for three minutes:
Before you swear off hand dryers forever, there is conflicting evidence. A 2000 study published by the Mayo Clinic, found “no statistically significant” hygienic difference between dryers and paper towels.
For what it’s worth, the University of Connecticut added paper towels to all 36 bathrooms surveyed in the study — so they may be onto something.