Reliably producing the smell of a damp cleaning cloth in the laboratory may sound surprising, but it is an important technique for investigating laundry malodor and comparing countermeasures. In a 2021 study, a model combining cotton fabric, three bacterial species, and bovine tallow reproduced a musty, pungent fabric malodor.
The researchers not only established conditions for generating the odor, but also examined which compounds formed and whether washing could suppress subsequent odor development.
Why make smelly fabric?
Household laundry carries diverse microorganisms from skin, washing machines, and other sources. Fibers, soils, moisture, and drying conditions also vary from one occasion to another. As a result, similar washing does not necessarily produce the same odor every time.
The researchers aimed to create a test system that would generate an odor reminiscent of wet, dirty fabric under standardized conditions. Such a system would make it easier to investigate odor compounds and bacterial combinations, and to compare washing methods.
Finding a strong, persistent combination among six bacterial species
The study used culture-collection strains of six bacterial species known to be associated with skin, clothing, or washing machines. Each was tested alone and in several three-species combinations.
The researchers used cotton squares measuring 2 cm on each side. They added a mixture containing bovine tallow as a nutrient source standing in for sebum soil, and incubated the fabric at 27°C and 84% relative humidity. In a preliminary assessment, five people evaluated odors on days three and seven.
The combination of Micrococcus luteus, Staphylococcus hominis, and Corynebacterium jeikeium proved particularly suitable. It produced strong malodor by day three, which persisted on day seven. Daily observations over 14 days found the strongest odor on day seven, with no further increase afterward.
Some bacteria generated odor alone, but mixtures could either intensify the smell or produce very little odor. It was not enough simply to have the same number of species: which bacteria were cultured together mattered.
A musty, pungent fabric smell to human assessors, too
Next, 14 assessors selected from university staff received training and evaluated samples from four bacterial combinations. After five training sessions, their individual descriptors and intensity ratings were recorded, with each sample evaluated three times.
The three-species mixture above differed clearly from the other combinations, with a musty character and a pungent impression in the nose. Assessors agreed relatively well on these two features, whereas use of the descriptor cheesy varied more between people.
This step checked whether the model reproduced the fabric malodor people actually perceive, rather than merely yielding numerical evidence of bacterial growth.
Sulfur-containing compounds and odors still without names
Volatile compounds released from the fabric were separated by gas chromatography and examined using mass spectrometry and GC-O, in which a person smells the column outlet. This analysis was separate from the 14-person assessment of the fabric’s overall odor.
Candidate compounds included cabbage-like dimethyl disulfide (DMDS), musty/cabbage-like dimethyl trisulfide (DMTS), and indole. The researchers also detected p-cresol, with animal-like or urine-like notes. Among the samples compared, the three-species model had the largest peak-area proportions for DMDS and DMTS. These proportions describe the composition of analytical signals, however, not absolute quantities in the fabric or shares of perceived intensity.
Importantly, there were also unidentified odor regions strongly reminiscent of wet-fabric malodor. Indole smelled strong, while DMDS and DMTS smelled weak when separated individually, but the overall malodor consisted of multiple compounds. The identified substances alone did not yet explain the entire wet-fabric smell.
Comparing whether odor develops again after washing
As another application of the model, the researchers washed samples in laboratory equipment for 60 minutes at 30°C. They compared washing without a washing agent with conditions containing 0.4% or 0.8% benzalkonium chloride (BAC), then incubated the samples for another seven days before examining bacterial counts and odor.
After seven days, culturable counts were about 100 million CFU/cm² in unwashed controls, about 100,000 CFU/cm² in fabric washed without a washing agent, and about 400 CFU/cm² with 0.4% BAC. At 0.8%, no bacteria were detected by this method. Washing without an agent also weakened the malodor, while assessors detected no malodor under either BAC condition.
These figures reflect the results after subsequent incubation, not simply bactericidal activity immediately after washing. They showed that odor can be undetectable even when some bacteria remain, and that the model can be used to compare ways of preventing malodor development.
The tests used cotton fabric supplemented with bovine tallow and specific bacteria. Extending the findings to household soils and microbial communities, other fibers such as polyester, and actual drying conditions is a task for future work. The BAC concentrations were research conditions, not recommendations for household additions or product dosing.
Summary
Culturing three bacterial species with bovine tallow on cotton reliably produced a wet-fabric malodor that was more musty and pungent than other combinations. Alongside sulfur-containing DMDS and DMTS, indole, and other compounds, strong unidentified odors were found. This provided a starting point for studying malodor as a combination of microorganisms and compounds.
After seven days of post-wash incubation, washing alone reduced bacterial counts and malodor, while malodor was not detected under the BAC-supplemented conditions. The study’s contribution was to build an experimental model that reproduces odor development and allows countermeasures to be compared under the same conditions.
The paper declares no external research funding and no competing interests. The acknowledgments mention Symrise’s assistance with GC analysis, and one author was affiliated with the company when the paper was published.
Reference
Zinn, M.-K., Singer, M., & Bockmühl, D. (2021). Smells Like Teen Spirit—A Model to Generate Laundry-Associated Malodour In Vitro. Microorganisms, 9(5), 974. https://doi.org/10.3390/microorganisms9050974
