shower-head-biofilm

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A shower head biofilm is the thin layer of microorganisms that builds up on the inside surfaces of a shower hose and its tubing. The two research papers checked for this guide describe that layer as a place where bacteria and other microbes gather and grow. They measured what was in it, but they did not examine how to remove it. This guide covers what the studies found, what the biofilm contains, and where the evidence stops.

Quick answer

• The sources do not give a formal definition of biofilm. This guide uses the word the way the two papers use it: a community of microorganisms living on a plumbing surface.
• One 2015 laboratory model found Mycobacterium avium complex (MAC) at up to 7.0 × 10 4 copies/cm 2 and Legionella at up to 2.0 × 10 3 copies/cm 2 in biofilm on flexible shower tubing.
• A 2023 study of 85 shower hoses found complex communities of bacteria and eukaryotes, including protists. Most of the organisms could not be named to genus level.
• Neither paper tested a cleaning, descaling, or disinfection method for the biofilm. The sources do not say how to treat a shower head biofilm.

Why a shower hose can grow a biofilm

The 2015 model study gives the clearest general explanation. Its authors write that “Showers provide an ideal niche for bacterial biofilm formation, which enables both pathogenic and opportunistic microorganisms to accumulate in large numbers.” They add that these organisms are then “dispersed into the passing water and aerosolised by the showerhead”

The 2023 paper, by Cavallaro and colleagues, lists three conditions that favour growth in shower hoses. In their words: “Three main factors promote microbial growth here: (i) temperature, which is often warmer in the last meters; (ii) flexible materials that leach organic carbon; (iii) usage patterns that often create extensive stagnation periods” The paper attributes these three factors to an earlier study, Proctor and colleagues (2016), which was not opened for this guide. The 2023 authors do not measure the three factors in their own samples, so they are background, not findings from the 85 hoses.

The 2023 paper also says that the hoses it studied were “from the same manufacturer,” “of similar operational age,” and “fed from the same building plumbing system.” That is a useful limit. The sample shows what biofilm looked like in one set of hoses. It does not show how biofilm varies across different brands, materials or water supplies.

What lives in the biofilm

The 2023 paper is the more detailed source on the community. It reports that “Shower hose biofilms fed with non-chlorinated drinking water consist of complex and diverse prokaryotic and eukaryotic communities” Across the 85 hoses, the sequencing found 1518 bacterial ZOTUs and 1389 eukaryotic ZOTUs. The paper counts Zero-Radius Operational Taxonomic Units (ZOTUs), which are sequence-based units rather than named species, so the figures are counts of sequence types.

Most of the community could not be named. The paper reports that “unclassified taxa at genus level accounted on average for 64.4±1.4% of the bacterial community and 85.3±1.2% of the eukaryotic community.” The authors say that these numbers “represent a gross underestimation of the true diversity” Among the named bacteria, the paper lists Meiothermus, H16 and Caulobacter as the most abundant genera, but it gives the abundance only as an average, and it does not say whether those groups cause disease.

The eukaryotes are the more unusual part of the picture. Protists are single-celled eukaryotes. The 2023 paper notes that “Legionella are able to infect a variety of eukaryotes such as amoebae, excavates, and ciliates” It also says that “Our dataset identified several associations with protists proposed as Legionella hosts.” It names Vannella, Echinamoeba and Hartmannella (now Vermamoeba) as groups linked to low Legionella abundance in its samples. The authors do not claim that these protists control Legionella in a shower, and they note that such associations are hard to interpret from sequencing data alone.

Bacteria found in the biofilm

The 2015 model reports the two organisms it looked for. In the model biofilm on PVC tubing, the authors measured MAC at a maximum of 7.0 × 10 4 copies/cm 2 and Legionella at a maximum of 2.0 × 10 3 copies/cm 2. These are measurements of gene copies by qPCR, and the authors note that “qPCR does not differentiate between viable and killed cells” The presence of DNA therefore does not show that the organisms were alive.

The 2015 authors sampled the biofilm by swabbing the pipe surface. They describe this as sampling “not from the bathing medium to characterise the established biofilm population.” The same paper measured how the biofilm changed over time. It states that “the concentration of biofilm changed over time, although no trends were observed.” In other words, the level of organisms rose and fell across the weeks, but the study did not find a steady pattern that would let a reader predict when a hose becomes heavily colonised.

The 2015 paper also says that MAC is “generally accepted” to be increasing in incidence, and it links that possibility to the change “from bathing to showering” This is a hypothesis cited by the authors, not a finding of their model. The model does not measure disease.

What happened when the biofilm dried

The 2015 model compared two tubing sections. One stayed filled with water between uses, and the other drained dry. The authors found “no significant difference” in the MAC and Legionella levels between the two sections at each time point. They conclude that “allowing shower tubing to dry between usages will not reduce the risk for Legionella or MAC colonisation.”

The same paper also tested the effect of flushing. Its wording is direct: the once-a-day flushing “did not provide sufficient shearing force to remove biofilm or prevent its formation.” This is a finding about one flushing schedule in one model. It does not show what a stronger or longer flush would do, and the sources do not examine one.

These two results are the closest the sources come to advice about the biofilm itself. Both are negative results: drying and once-a-day flushing did not reduce the organisms in the model. Neither result describes a way to remove a biofilm that has already formed.

What the sources do not say about treatment

• The sources do not give a cleaning, descaling, or disinfection method for a shower head biofilm. No vinegar, chlorine, heat, or mechanical method was tested as a treatment.
• The 2015 paper replaced its sampling sections with clean tubing during the experiment. That was part of the experiment’s design, not a tested treatment, and the paper does not report whether replacement reduced the biofilm.
• The 2023 hoses were “replaced and transported to the laboratory in sealed bags” for sampling. The paper does not study what happens when a hose is cleaned in a home.
• The sources do not say how long a biofilm takes to form in a home, or how often a shower head or hose should be replaced.
• The 2023 paper notes that the hoses were fed with non-chlorinated water. The sources do not show how chlorinated water changes the biofilm.

Readers who find information about treatment should check whether the source is a peer-reviewed study that tested the treatment, or an opinion. Neither of the two sources checked here examined a home method, so this guide does not recommend one.

How we chose

This guide uses two peer-reviewed open-access papers, both opened on 2026-10-28. The 2015 paper was chosen because it measured microorganisms in the biofilm of flexible shower tubing and tested drying and flushing. The 2023 paper was chosen because it sampled biofilm from real shower hoses and profiled the community in them. Both are research papers, not product pages, and no product is recommended.

The two papers describe the 2023 setting differently. The abstract calls it a multiunit residential building, and the methods section says the samples came from a retirement facility in Switzerland. This guide reports both descriptions and does not choose between them.

What we could not verify

• Whether the 2015 model, which used PVC tubing, water at 35 °C and a fixed pattern of use, reflects a home shower with different hoses and habits.
• Whether the 2023 community profile applies to hoses in other buildings, countries or water supplies. The paper does not give use habits or water temperature for the hoses.
• Whether the organisms counted by DNA methods were alive. The 2015 paper says the method cannot tell viable cells from dead ones.
• The three factors that the 2023 paper attributes to Proctor and colleagues (2016). That paper was not opened for this guide.

FAQ

Is shower head biofilm the same as the slime I see in a shower head?

The sources do not describe what a visible film or residue looks like. They describe biofilm in terms of the microorganisms sampled from hoses and tubing. A visible deposit may or may not match the samples in these papers.

Which organisms did the studies find in shower biofilm?

The 2015 model measured MAC and Legionella. The 2023 study sequenced bacteria and eukaryotes, including protists, and reported Legionella among them. Most of the community was not named to genus level.

Does drying a shower head remove the biofilm?

The 2015 model found no significant difference between dry and wet tubing for MAC or Legionella. The authors conclude that drying does not reduce the risk of colonisation in the model.

Does flushing the shower remove the biofilm?

In the 2015 model, once-a-day flushing did not provide sufficient shearing force to remove the biofilm or prevent its formation. The sources do not examine other flushing schedules.

What cleaning method works on shower head biofilm?

The sources checked do not examine a cleaning method, so they cannot say which method works. This guide does not give a cleaning protocol.

Who should be careful about shower biofilm?

The 2015 paper cites lung disease from MAC and notes “disseminated infection in immune compromised patients” It does not give a general risk ranking for healthy people. If you have a weakened immune system, chronic lung disease, or you care for someone who does, talk to a doctor before changing your routine.

Bottom line

A shower head biofilm contains bacteria and protists, and the studies found MAC and Legionella in it. The two papers show that drying and once-a-day flushing did not reduce the organisms in their models. They do not show how to clean a biofilm, and anyone with a weakened immune system or lung disease should speak with a doctor about water exposure.

Sources

• Whiley H, Giglio S, Bentham R. “Opportunistic Pathogens Mycobacterium Avium Complex (MAC) and Legionella spp. Colonise Model Shower” Pathogens. 2015;4(3):590-598. https://pmc.ncbi.nlm.nih.gov/articles/PMC4584274/ (opened 2026-10-28)
• Cavallaro A, Rhoads WJ, Sylvestre E, et al. “Legionella relative abundance in shower hose biofilms is associated with specific microbiome members” FEMS Microbes. 2023;4:xtad016. https://pmc.ncbi.nlm.nih.gov/articles/PMC10496943/ (opened 2026-10-28)