That Slime Gathering On Your Showerhead Might Actually Be Pretty Dangerous

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Your bathroom may be hiding a very dirty little secret.

Faucets, toilets, and hoses – bacteria thrive on nearly everything in your home where water is used. According to new research published in mBio, one particular spot is especially oozing with microorganisms: your showerhead. While most of these microscopic organisms are harmless, some strains of nontuberculous mycobacterium have been shown to correlate with life-threatening lung infections.

Mycobacterium is the most common genus of bacteria that grows in the slimy stuff on your showerhead known as “biofilm,” often harboring “abundant mycobacterial communities that vary in composition depending on geographic location, water chemistry, and water source.”

Started in 2017, researchers analyzed DNA from more than 650 showerheads in the US and 13 European countries from citizen scientists who swabbed the inside of their showerheads with special kits. These kits were then sent to researchers for DNA sequencing to determine what species of bacteria were the most abundant. All data from the Showerhead Microbiome Project is available online

They found mycobacteria was most commonly found in US urban households over households that run using well water or those in Europe. Oddly enough, households with water treated with chlorine disinfectants had particularly high numbers of certain mycobacteria, which are somewhat resistant to the those used more heavily in the US allowing European bacteria the opportunity to thrive and outcompete the disease-causing strains. Once exposed to water vapor, the mycobacteria become aerosolized and may be responsible for the transmission of nontuberculous mycobacterial (NTM) lung disease when inhaled.

“There is a fascinating microbial world thriving in your showerhead and you can be exposed every time you shower," researcher Noah Fierer said in a statement. "Most of those microbes are harmless, but a few are not, and this kind of research is helping us understand how our own actions – from the kinds of water treatment systems we use to the materials in our plumbing – can change the makeup of those microbial communities."

Showerhead materials matter too. More mycobacteria were found in metal showerheads than plastic ones, likely because plastic leaches chemicals that would support diverse bacterial communities that hinder mycobacteria from becoming too abundant.  

Perhaps most notably, the team found the highest numbers of mycobacteria corresponded to “hot spots” of lung disease in Southern California, Florida, and New York. Understanding why and how these hotspots exist could help inform a greater understanding of how NTM is transmitted.

"It's important to understand routes of mycobacterial exposure, especially in the household. We can learn a lot from studying the biofilm that accumulates inside your showerhead, and the associate water chemistry,” said lead study author Matt Gebert. “There is a lot of interesting ecology at work, and it allows us to begin to understand how it can impact human health.”

You have to give the little buggers some street cred. As the authors note, they have to tolerate rapid temperature fluctuations, not to mention long intervals of stagnation followed by highly turbulent flows.

NTM is difficult to treat and on the rise in the US for reasons scientists aren’t quite sure of. Even so, the team says it’s no excuse to skip out on your hygiene duties.

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