Do Cotton and Polyester Shirts Smell Different After Exercise?

After exercise, shirts can smell different depending on their fabric, even when they have absorbed sweat in much the same way. A 2014 study compared shirts stored for 28 hours after an hour of exercise and found that those made of 100% polyester were rated stronger-smelling and more unpleasant than those made of 100% cotton.

The researchers investigated more than odor. They examined the bacteria on the shirts and, in a separate experiment, tested whether different fabrics favored the growth of different bacteria. The findings suggested that clothing does not simply collect sweat: it also provides a microbial environment distinct from the skin.

Distinguishing skin odor from clothing odor

Callewaert and colleagues primarily wanted to find out which bacteria were present on worn clothing, whether bacterial communities differed by fabric, and how their odors differed. Cotton and polyester were the central comparison.

Bacteria transfer from underarm skin to clothing along with sweat and sebum. Once on clothing, however, conditions such as air, moisture, and available nutrients differ from those on the skin. The study sought to examine clothing microbes rather than treating them as a simple copy of the skin microbiome.

Assessing 26 people’s shirts 28 hours after exercise

Twenty-six healthy men and women aged 20–60, living in the same region of Belgium, participated in an hour of intensive cycling. Each wore a freshly washed T-shirt made of cotton, polyester, or a blend. The researchers did not randomly assign fabrics or have the same people wear different fabrics in turn.

After exercise, the shirts were sealed in individual bags and stored in the dark at 20°C for 28 hours. Seven selected and trained assessors then evaluated pleasantness, odor intensity, mustiness, ammonia-like odor, sweatiness, sourness, and related characteristics. Importantly, the results do not describe odor during wear or only immediately after removing the shirts.

Bacteria were extracted from the whole shirts and examined using cultivation and DNA-pattern analysis. Samples were also taken from participants’ underarm skin for comparison with the clothing communities.

Polyester smelled stronger and more unpleasant

When pure cotton and pure polyester shirts were compared, polyester had a stronger odor and lower pleasantness. On a pleasantness scale from −4 to +4, the mean was −0.61 for cotton and −2.04 for polyester, placing polyester further toward the unpleasant end.

Characteristics including mustiness, ammonia-like odor, sweatiness, and sourness were also stronger for polyester, with particularly large differences in sourness and mustiness, among others. The differences involved several odor qualities rather than a single impression of “more sweat.”

However, participants’ diets and usual hygiene habits were not standardized. Although there was no clear difference between the two fabric groups in the frequency of deodorant or antiperspirant use, garment construction and individual differences were not fully matched. The observed differences therefore cannot all be attributed to a causal effect of fabric alone.

The bacteria on shirts were not the same as those on underarm skin

Various bacteria were found on the clothing, with considerable differences between individual shirts. Among them, the genus Micrococcus was prominent on polyester shirts and shirts containing synthetic fibers. Staphylococcus was widely detected on both cotton and synthetic fabrics.

By contrast, Corynebacterium, which occurs on underarm skin, was not detected or isolated from clothing in this experiment. DNA patterns also differed markedly between skin and shirts. This suggested that transferred bacteria do not all grow equally: the clothing environment favors some over others.

The difference illustrates why it is useful to study underarm skin odor separately from the odor of clothing after it has been removed.

A separate culture experiment also found fabric-dependent growth

The researchers next inoculated each of seven fabric types, polyester, acrylic, nylon, fleece, viscose, cotton, and wool, with five representative skin-associated bacterial species separately. They incubated the sterile fabrics at 37°C for three days and measured the bacteria recovered.

Micrococcus luteus grew readily on polyester, whereas there was no clear increase on cotton. This complemented the association between polyester and Micrococcus observed on the post-exercise shirts.

Not all bacteria favored the same fabric, however. Nylon, for example, supported a marked increase in Propionibacterium and some other bacteria while suppressing Micrococcus. Wool supported the growth of many bacteria. Corynebacterium jeikeium did not grow on any fabric under the culture conditions used.

Few bacteria were recovered from viscose, but the efficiency of extracting bacteria from that fabric was also low. Further checks are therefore needed before concluding that it does not support bacterial growth.

Ease of attachment alone could not explain the findings

To explore why Micrococcus grew on polyester, the researchers also examined interactions between bacteria and material surfaces. Because droplets soak into fabric, they used PET plates as a substitute for polyester and cellulose plates as a substitute for cotton, estimating interactions from liquid-droplet contact angles.

These measurements showed no clear difference in bacterial interactions with the two materials. At least as assessed by this method, attraction to the surface alone could not explain the difference in growth.

The authors discussed differences between fabrics in retaining and releasing odor compounds, as well as the possibility that oxygen and nutrient conditions favor particular bacteria. However, this experiment did not track the production of odor molecules by each bacterial species. How much particular bacteria contributed to the difference in shirt odor still requires investigation.

Summary

Among garments stored for 28 hours after exercise, 100% polyester shirts were rated stronger-smelling and more unpleasant than 100% cotton shirts. Bacterial communities also differed, with Micrococcus prominent on polyester; a separate culture experiment supported its greater growth on that material.

Growth nevertheless depended on the particular combination of bacterium and fabric, and simple differences in attachment could not explain it. Understanding clothing odor requires considering both the properties of the material and the kinds of bacteria that grow on it.

This research was supported by the Flemish government and Ghent University. The authors declared no conflicts of interest.

Reference

Callewaert C, et al. Microbial Odor Profile of Polyester and Cotton Clothes after a Fitness Session. Applied and Environmental Microbiology. 2014;80(21):6611–6619. doi:10.1128/AEM.01422-14.