It’s important to wash your hands frequently, but how you dry them can make a huge difference.

Hot air hand dryers are touted as the eco-friendly alternative to paper towels, but they may be contributing to pollution — in the bathroom itself, at least.

Air hand dryers suck up fecal matter from the bathroom air and spray it onto users’ hands, a new study published by the American Society for Microbiology found. Bathrooms without hand dryers are cleaner than bathrooms with hand dryers, the study showed. Researchers found only six pathogens in bathrooms with towels for drying compared to 254 in bathrooms with hand dryers.

“These results indicate 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,” the authors said.

The researchers behind the study at the University of Connecticut School of Medicine tested 36 public bathrooms across campus for a bacteria called Bacillus subtilis or PS533, which is found in soil and fecal matter, though does not necessarily lead to illness. When lidless toilets flush, they send this bacteria flying into the air in a “toilet plume,” as the phenomenon has been dubbed. Air dryers suck up the bacteria, which includes potential pathogens, and redistributes it into the air.

According to the Centers for Disease Control and Prevention, people should wash their hands with soap and water, scrubbing hands for at least 20 seconds to create friction that helps lift dirt and microbes from the skin. While it has a number of guidelines for washing hands, its advice for drying hands is less concrete. “The best way to dry hands remains unclear because few studies about hand drying exist, and the results of these studies conflict,” the CDC said.

This study suggests drying with a clean towel is much cleaner than drying with hot air. Researchers added paper towels to all of the bathrooms included in their investigation after the study.

Bathrooms aren’t the only places were icky bacteria lurks: Half of all office coffee cups have fecal bacteria on them, a 2014 study found, and ice from coffee chains has also been shown to carry fecal bacteria. The majority of exercise equipment also has bacterial and viral pathogens, a 2006 study found, even after it is disinfected. Aisle seats in planes, trains, and theaters, which are more likely to be touched by passersby, carry risk of infection including diarrhea and vomiting. When access to soap and water is limited, a hand sanitizer that is at least 80% alcohol works nearly as well, experts say.