The shower is where we go to get clean, so most people probably don't realize their showerhead is literally teeming with microbes. Scientists are recruiting people across the US who are willing to provide samples from their showers, so they can catalogue which bacteria are in there and how they compare in different parts of the country.
"We're interested in the microbes inside your home," Noah Fierer, a microbial ecologist at the University of Colorado, told me. In the past several years, scientists have started to define the many, many communities of bacteria and other microbes that thrive inside our guts, on our skin, and everywhere around us, including in our houses.
We spend most of our lives inside, he told me, yet we have almost no idea which species of bacteria we're interacting with, or the impacts they're having on us—good and bad.
In a paper published in 2015, Fierer and his collaborators described the stuff they found living in household dust. "We had thousands of [people] across the US sample the dust on the door trim in their homes," he said. "And you see all sorts of patterns," including geographical ones: The fungal communities they found in the homes in Arizona were different than in New York City, and indoor and outdoor dust samples were different, too.
Beyond that, bacterial communities that live in household dust were influenced by the number of people in the home, and who they were—things like the male-female ratio, and whether there were pets in the home, all seemed to matter.
"Of course, there are allergens and pathogens, things we don't want in our home," Fierer said. "But a lot of organisms fall into the grey area. They're probably harmless," and some of them might be important to helping develop our immune system.
Before we can really understand these microbes and what they're doing to us, we need to figure out which ones are even there, and establish some kind of a baseline. That includes the ones living in our shower, a special microbial environment unto itself.
"It turns out there are a lot of microbes living in your showerhead," said Fierer, who's working on this with researchers from North Carolina State University and National Jewish Health, a respiratory hospital in Denver.
"Taking a shower is a major way we get exposed to environmental microbes," he continued. "That's not necessarily good or bad. I don't want people freaking out about it." Fierer emphasized this many times in our phone call.
One bug that's been found in household plumbing, and might be of concern, is Nontuberculous mycobacteria (NTM), which can cause lung infections. These microbes are found in showerheads across the country, although cases of the disease are more frequently diagnosed in some geographical areas than others.
For reasons that scientists don't understand very well right now, there seem to be hotspots for the disease in Hawaii, Florida, and the New York metropolitan area, Fierer said.
Understanding that better is a main motivation for the showerhead microbiome project. Fierer and the researchers are recruiting people across the US. They're hoping that 2,000 households or so send in samples, especially from Hawaii, where the NTM infections are more prevalent. (They'll be expanding the recruitment to Europe, too.)
By fall, they plan to begin DNA sequencing and other types of analysis on the samples. Everyone who participates will get updates on what's living in their showerhead.
But if you decide to send in a showerhead sample, don't have high hopes that these scientists will tell you exactly how grody it is. "We know too little to tell you immediately what to do with regard to your shower," says a website about the project, run by researcher Rob Dunn. "We won't be able to say, tomorrow, 'this is the solution,' or 'your shower is healthy.'" That's because the answer depends not just on what's living in your shower, but what's living in, on, and around you, Dunn's site says.
"A microbe that's beneficial to one person may be dangerous to another," it explains.
In the meantime, get used to the idea that, even when you're taking a shower, a whole pile of microbes are all in there with you, floating around in the steam.