The Showerhead Microbiome Project

Photo by Lea Shell- Rob Dunn Lab

Series of six ‘Van Leeuwenhoek plates’; Algae, Eye from bottom side of lens, HIV virus, Pentagrams, Bacteria, and Organisms, bacteria and lumps by Bram Zwartjens. Photo by Lea Shell – Rob Dunn Lab

When Antonie van Leeuwenhoek, the first microbiologist, began to study microscopic life, he did so with a sense of stupefied awe. He could scarcely believe what he was seeing (and those to whom he sent reports about his observations didn’t believe at all). Van Leeuwenhoek would go on to look through his tiny microscope at the life everywhere around him in his home and in his city of Delft, Holland. Chief among the places he looked were those in which he could find standing water. He searched gutters, glasses full of water and pepper, his neighbor’s mouth, and more. In as much as Leeuwenhoek was working in Delft, Holland in the 1600s he did not have a showerhead but rest assured, if he did have one, he would have checked it too. They were his sort of habitat, both damp and domestic.

Water sustains life. The same is as true of the ocean as it is in your body or home. Showerheads are often wet and so offer a realm in which life can live. That life can colonize showerheads either from the water itself (tap water contains many kinds of life, from bacteria to nematodes to crustaceans, as does bottled water), or from those organisms that bounce back up onto the showerhead from your body when you stand and cleanse. But one thing that is unique with regard to showerheads compared to those places that Leeuwenhoek studied is that while they are often wet, they are just as often dry. They are the desert washes of your home, places of both bounty and hardship. This mix of soaking wet and bone dry provides circumstances that favor unusual sorts of microbes. When you take a shower these are microbes to which you are exposed, daily. The microbes on your showerhead become airborne as you shower and then fall down onto your body but also into your mouth and nose. As you sing they settle. These settling microbes include both species that are potentially bad news (“pathogens” in the lingo of my tribe such as Legionella which causes Legionnaire’s disease) and those that are potentially beneficial. One group of microbes that fits both of these bills (microbes are almost never simple) is the unusual genus Mycobacterium. Some Mycobacterium are pathogens. Others may be beneficial. Others still are pathogens in some contexts and beneficial in others. This much we know. What we don’t know is why some showerheads seem to be covered in a hairy skin of the stuff and other showerheads (even old, gunky, terrible looking ones of the sort you might find in the hostel of your nightmares) have none. Why? We don’t know. That is what we want to figure out.

Participants will receive a simple kit to sample their showerhead and water.

Participants will receive a simple kit to sample their showerhead and water.

We sampled showerheads around the United States and Europe by engaging participants, folks like you (or like Van Leeuwenhoek) with both an interest in the life around us and, well, a shower, to help us out. Now that showerheads are sampled, we are using diverse approaches to study what lives on your showerhead. Noah Fierer’s lab is looking at whether we can grow Mycobacterium from your showerhead and if so how many (and what kinds). We are looking at what other microbes are present. We are using statistical approaches to see what seems to be associated with the differences among houses, water systems and even countries in the biology of showerheads.

We have some hypotheses as to what determines what lives on showerheads. We think the water matters. We think the kind of showerhead may matter. We think it may even matter if you have, on your showerhead, amoebas that eat the mycobacteria and, in doing so, keep them in check, the leopards of your bathroom Serengeti. But we’ll also be interested to hear what you think might be important. We know so little about the life around us that your observations are likely to change our perspective.

As you consider participating we want to say in advance three things, three things we can’t make clear enough. First, science is slow. The time between when you send a sample in and when you know what is on your showerhead may be a while. Our guess now is that it will take about a year. If you are OK with delayed gratification, we are the project for you. Second, we take your insights seriously. If you have an idea about this project (or have noted something more generally that you think might be of interest with regard to water ecology), let us know (via the sign up). Third, we know too little to tell you immediately what to do with regard to your shower. We won’t be able to say, tomorrow, “this is the solution,” or “your shower is unhealthy.” In part this is because the answer depends not only on the biology of your showerhead, but also on your biology. A microbe that is beneficial to one person may be dangerous to another person, for example someone who is immunocompromised.

Sign Up to Join the Showerhead Microbiome Project!

Project Information


Gebert, M.J., Delgado-Baquerizo, M., Oliverio, A.M., Webster, T.M., Nichols, L.M., Honda, J.R., Chan, E.D., Adjemian, J., Dunn, R.R. and Fierer, N., 2018. Ecological analyses of mycobacteria in showerhead biofilms and their relevance to human health. Mbio9(5), pp.e01614-18.

Project Team Members

Noah Fierer (Project Lead, University of Colorado, CIRES) and his lab will use molecular tools (picture a tiny, chemical decoder ring) to identify the microbes present in your shower head. Noah is an expert in soil bacteria but every so often finds himself lost in the wilderness indoors.

Matthew Gebert (University of Colorado Boulder), a research technician in the Fierer Lab, leads sample processing, sequencing and bioinformatics.

Rob Dunn (NC State Dept. of Applied Ecology) and his lab will coordinate sample processing in the U.S. Rob is an expert in the ecology of life on and around humans, from belly buttons to backyards.

Lauren Nichols (NC State Dept. of Applied Ecology), a research assistant in the Dunn Lab, leads participant recruitment and data management.

Nate Sanders (Center for Macroecology, Evolution and Climate at the University of Copenhagen) and his lab will coordinate sample processing in Europe. Nate is an expert in global scale patterns of the diversity of life, be that the diversity of ants, trees, or, well, shower life.

Christopher Lowry (Dept. of Integrative Physiology at University of Colorado Boulder) will explore how novel Mycobacteria species/strains interact with our immune system, in hopes of understanding potential health benefits of Mycobacteria exposures. Christopher is expert in potential health benefits of Mycobacteria exposures, including increased stress resilience.

Jennifer R. Honda (Univ. of Colorado Anschutz Medical Campus & National Jewish Health) is an NTM microbiologist who knows the special sauce needed to grow and maintain NTM in the lab! She will also help to understand why some NTM are more likely to be found in showerhead biofilms than others and their impact on susceptible host populations.

Ed Chan (National Jewish Health) is a lung physician with special interests in infectious lung disease. He will help Dr. Honda culture the bacterial isolates and help relate what bacteria are found on shower heads to known human lung disease.

Sponsored in part by the Jelsa Institute for the Study of the History of Life, Civilization and Wine.