You'd expect public bathrooms to be pretty gross, especially in and around the toilet. By the time people have washed their hands and headed towards the dryers, however, you'd hope that most of people's gross bacteria would have been washed away down the drain. Right?

Nichole Ward, a student from Carlsbad, California, decided to test that for her microbiology class. She collected bacteria from a dryer by placing an open petri dish inside it for three minutes, and then incubated the bacteria collected. She posted the results of the experiment to Facebook, and made the post public after her grossed-out friends demanded she alerted the world.

The post went viral because, well, the image of the petri dish is really, really gross.

"Ok guys.. ready to have your mind blown?!" the student wrote on Facebook. 

"This here, is what grew in a petri dish after just a few days. I stuck the open plate in a Dyson hand dryer of a public bathroom for a total of three minutes. Yes, three only. DO NOT EVER dry your hands in those things again."

Pretty grim, no? 

People were rather alarmed by the experiment.

But it gets worse. Nichole said that several of the strains of microorganisms she found could cause disease.

"This is the several strains of possib[ly] pathogenic fungi and bacteria that you’re swirling around your hands, and you think you’re walking out with clean hands. You’re welcome." 

So why is there so much bacteria collected in the dish, and should you be worried?

While it's true that a lot of normal bacteria collected on your hands will look pretty gross under a microscope (see the image below for how gross an 8-year-old's hand is after playing outside), the petri dish does seem especially gross to our IFLScience biologists. This is not a normal background level of bacteria.

^{This image is of a handprint of an 8-year-old after playing outside. Most of the bacteria are completely harmless, and will help the child build immunity.}

As for how it got there, one commenter pointed out that the dryers pull in air from the bathroom, floating bacteria and all, and then fire it at your hands at high speeds. Which is a pretty grim idea if you really think about it.

However, Dyson said that they were unsure about the methodology used by Nichole in her experiment for class.

"We’re very surprised to see these results," they told ABC Action News.

"All Dyson Airblade hand dryers have HEPA filters that capture particles as small as bacteria from the washroom air before it leaves the machine."

They pointed out that the machines are trusted by everyone from hospitals to food manufacturers around the world. It could be that Nichole conducted her test on a dryer with a dodgy filter, or that it was a particularly dirty bathroom.

Nichole stressed that her post, which has been shared by over half a million people, wasn't there to terrify anybody, just to raise awareness of bacteria in public restrooms.

If you are really worried or grossed out by the experiment, however, maybe opt for paper towels.