How much of your information about science comes from the news? Intentionally or not, TV stations, newspapers, and magazines often report scientific findings incorrectly, or even exaggerate them to the point of causing panic. In our new series, Bad Science, we highlight stories about science reporting gone wrong— and let you know what the real facts are.


Let’s talk about how gross our houses are. Anyone who has recently picked up a trashy magazine at the checkout line knows that sponges, light switches, keyboards, phone screens, and probably every other item you aren’t spraying with ethanol on a daily basis is dirtier than your toilet seat. A quick search on “reducing the spread of germs” will lead you down the rabbit hole of bacteria-ridden daily activities.

Thought you wanted to go to the gym today? Did you know that “germs thrive in the warm, sweaty atmosphere” you’ve been daring to visit on a daily (okay, monthly) basis?  Did you want to wash the dishes today? Hm, better read about how filthy that kitchen sink is. I’ll bet you’re starting to feel like a shower right about now. Whoops—don’t get near that shower curtain.

Don’t worry, this article isn’t actually about scaring you with germs and their insidious, ubiquitous presence. I’m leaving that to the health magazines and Buzzfeed articles, because it seems to be what they do best. Or at least, they do it a lot. Instead, my goal is to draw your attention to the real research process sadly ignored by these fear-mongers in favor of a snappy, terrifying headline. In 2004, CU Boulder professor Norman Pace collaborated with Scott Kelley, a professor at UCSD, on a study entitled “Molecular Analysis of Shower Curtain Biofilm Microbes” in which they analyzed the composition of microbial communities found in the “soap scum” on shower curtains collected from various locations in Boulder, CO.

This scum is actually an example of a biofilm, or a group of microorganisms that adhere to a surface with the aid of their sticky secretions. Unsurprisingly, the paper made a splash in popular media, appearing under headlines like “Daily Bathroom Showers May Deliver Face Full of Pathogens” and “Biohazard Lurks In Bathrooms”.

What did the publication actually show? By using a sequencing technique that relies on an initial Polymerase Chain Reaction (or PCR) amplification of a molecule known as ribosomal RNA, the scientists could determine the diversity of microbes present in the sample they pulled directly from the germy curtain. This is because every organism contains ribosomal RNA, but the ribosomal sequences are just diverged enough to allow for an accurate representation of which species, and in what approximate proportions, are present.

This cool technique has been used to look at the microbial diversity of much more than shower curtains—most people are now aware of the microbiomes present in our guts and on our skin, thanks to scientists like Rob Knight, a professor who recently moved from CU Boulder to UCSD. Knight, among others, has sequenced ribosomal RNA to examine the diversity of these close-to-home microbial environments, changing our understanding of what it means to be healthy.

In their publication, Kelley and Pace found that the soap scum on shower curtains is a teeming collection of bacterial species, some common, some not. Two of the most abundant bacterial groups were genera of proteobacteria, Sphingomonas and Methylobacterium. Other genera were found at low abundances, and the overall diversity is immediately apparent. Biofilms, whether they are found on a log in your backyard or the vinyl in your shower, are rich with a variety of species. No known pathogens, or microbes that can make you sick, were found in this particular study—which is perhaps not entirely surprising; who do you know who got sick recently from taking a shower?

From the popular coverage of this publication, you might think you were harboring the next drug-resistant super-bug on your innocuous-seeming shower curtain. Men’s Health Magazine called shower curtains Germ Hotspot Number One. The New York Times stressed the discovery of a particular species: Mycobacterium avium, closely related to tuberculosis. Is your pulse increasing yet?

To be fair, the published paper did include a warning: the results suggested that “shower curtains are a potential source of opportunistic pathogens associated with biofilms.” After reading that, I have a new resolution to clean my shower curtain monthly (okay, yearly). Some of the species they recorded are phylogenetically similar to pathogenic species. For example, they found species closely related to the Gordonia genera, a bacterial group that has been known to invade wounds and result in bacteremia and brain abscesses.

But to be clear, the authors of the study did not find pathogens—only similar species. In fact, most bacterial species are not pathogenic, despite their bad reputation. We simply tend to research, and be more aware of, species that do us harm. Overall, shower curtains probably are pretty innocuous… well, most of them. I’m looking at you, Pi Kappa Alpha.

To sum up, the reporting on this paper from the Pace lab wasn’t exactly incorrect. It’s true that there were many different kinds of bacteria found on multiple shower curtains, and the revelation that “soap scum” can be more accurately described as “biofilm” is a little, well, gross. But most of the reporting in daily newspapers and blogs about this paper over-represented the danger of a filmy shower curtain, playing to our fears instead of our curiosity.

The Pace lab used an incredible sequencing technique to examine the diversity living on a common household item. Now, ten years later, the public knows a little bit more about the “healthy microbiome” and all the good that bacteria can do for us.  Let’s revisit this work with some newfound perspective and stop buying into sensationalist reporting of microbial science.

By Alison Gilchrist

Posted by Science Buffs

A CU Boulder STEM Blog

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