You may not want to think about it as you're standing under the soothing jets of hot water, but every morning you step into the shower, you share that intimate space with millions of invisible microbes. Most of them live right there in your showerhead—and for the past few months, researchers have been trying to better understand how they might be affecting your health.
That research effort is known as the Showerhead Microbiome Project, and it's rooted in a simple fact of biology: We're constantly exposed to microbes—in dust, in the air, in our food, and from our pets. Some of that exposure is good; some is bad or totally innocuous. We often don't think about our environment as teeming with life, but the idea of a "microbiome" is just that—the collection of microorganisms inhabiting a particular environment, in a kind of mini-ecosystem.
You've probably heard of the human microbiome, the collection of microbes living inside and on the human body. Researchers have long studied what role these microorganisms play in human health, from digestion to detoxification to supporting and activating the immune system.
In recent years, we've learned that human microbiomes vary widely from person to person; even twins have distinct microbiomes. The closest similarities are found between similar body parts: The bacteria on my skin are different from the bacteria on yours, but they're more alike than the bacteria on my skin and in my gut.
We're estimated to be comprised of approximately the same number of bacterial cells as human cells, making for an incredibly complex system. Figuring out how changes in the human microbiome can affect us is a large-scale project; already we've found that low microbial diversity in the gut can have negative effects. That's one reason (among many) why researchers have looked closely at how we prescribe antibiotics—recognizing that not all microbes are invaders, but part of a beneficial ecosystem we carry everywhere.
The recent focus on showerheads is just the latest in a long line of things to which microbiologists have been giving a closer look. "Studying bacteria in the household isn't really anything new," says Matt Gebert, a research assistant working on the project, noting that scientists have also examined the microbes in cats, dust, sourdough, and armpits, to name a few. "We chose the shower because it's a common source of microbial exposure," he says. All that water splashing over you can carry microbes, which can enter the body through aerosolized drops or through ingestion of the water itself. Your showerhead also happens to be a great place for microbial life to persist—it's damp and warm, and amidst the steam and running water, microbes can travel back and forth between the showerhead and your body.
Gebert took pains to emphasize that this isn't a bad thing. Having bacteria in your showerhead doesn't place you at greater risk for infection or disease. You don't need to take on the Sisyphean task of scrubbing your showerhead clean. (It probably wouldn't stay that way for long, anyway.)
But that's not to say there couldn't be some unpleasant things hiding there: "One of our main concerns so far is looking for nontuberculous mycobacteria, which has been known to cause lung and skin infections, mostly in those with compromised immunity," he says. Cases of infection seem to be more prevalent in certain areas; building a catalog of showerhead microbiomes could help researchers understand why that's so. Does it have something to do with climate? Water chemistry (like pH balance, chlorine, or hardness levels) or source (well versus municipal)? Could there be something about the materials in the showerheads themselves that affects mycobacterial growth?
Again, Gebert isn't trying to scare people into never showering. He and his colleagues are examining a common source of bacterial exposure, trying to understand what's in it and how it may affect us. Knowing that nontuberculous mycobacteria are more prevalent in plastic showerheads, say, that interact with well water at a certain pH, would be useful information. It wouldn't tell you that every case of mycobacterial infection comes from a showerhead, but it would help us better understand one potential source. And given the complexity of the human microbiome, you might find positive interactions as well.
It's a little early to make any decisive claims about what they've found. "No one's ever done a study of this scale, so we weren't even sure we'd be able to pick up bacterial DNA just by sending people to swab their showerheads," Gebert says. They've sent out about 1,500 kits to the United States and Europe, and are hoping to cover all 50 states. Samples come back to the University of Colorado, where they've analyzed about 200 so far. Gebert says he's been surprised at the variety of microbes they've discovered, given that they weren't even sure the swabbing technique would reveal any bacteria.
The project, Gebert emphasizes, would be almost impossible without the recruitment of volunteers who take the time to put on a pair of gloves, unscrew their showerheads, and swab around to see just what's living in there. (You can sign up on the website if you'd like to participate.) But he also hopes it isn't just a one-way transaction, with scientists getting free data they couldn't otherwise obtain. Volunteers might also get a better understanding of the scientific process: It's not just a black box that produces knowledge; it's people asking careful questions, then defining ways to pursue the answers. Sometimes it's recruiting hundreds of other people to help. And ultimately, in this case, it's about making legible an invisible world, one that surrounds us every day, and affects us in ways we're just beginning to understand.