Sometimes the smell of sweaty clothes becomes less noticeable after they have been hung up for a while; sometimes it remains until the next day. Could these differences involve the way fibers take up odor compounds and subsequently release them into the air?
In 2024, Rachel H. McQueen and colleagues immersed bundles of six types of textile yarn in artificial sweat containing odor compounds and examined the compounds released into the air. Their aim was not simply to rank materials by how smelly they are. It was to develop an experimental way of studying the transfer of odor compounds through liquid sweat, an important route from body to clothing.
Odors acquired from air versus odors transferred in sweat
Experiments on clothing odor often expose fabric to airborne compounds and measure how much it takes up. Clothing in contact with skin, however, receives compounds along with liquid sweat. Compounds dissolved in water do not necessarily interact with fibers in the same way as compounds arriving from the air.
The researchers therefore compared cotton, mercerized cotton, viscose, wool, nylon 6.6, and polyester. Mercerized cotton is cotton treated to change characteristics such as fiber shape and water absorption; viscose is a regenerated fiber made from cellulose. To examine fiber differences while minimizing the influence of weaving, the researchers unraveled fabrics into yarns and made bundles equivalent to 1 gram of dry material.
They added nine volatile organic compounds associated with body and laundry odors to artificial sweat: four ketones, two aldehydes, and three carboxylic acids. After exposing the yarn bundles to this solution for about 30 minutes, they removed excess liquid and suspended the bundles inside bottles.
Measurements assessed compounds released into the air above the bundles 30 minutes, 3 hours, and 24 hours after treatment. Between measurements, the bottles were left uncapped in a fume hood to let the bundles dry and release compounds. Before each measurement, the bottles were capped for 30 minutes to allow compounds to accumulate in the air, then analyzed using a mass spectrometer called PTR-MS. This was not a study in which people wore clothing and rated its smell.
The material that releases most initially may not do so the next day
After 30 minutes, many ketones and aldehydes gave higher signals in the air above wool, nylon, and polyester than above cotton, mercerized cotton, and viscose. Nylon often had especially high mean values: for example, more 2-hexanone was detected above nylon than above the three cellulosic materials. However, its differences from wool and polyester were not all statistically clear.
The ranking changed over time. Ketones released from wool declined rapidly; after 3 hours, three of the four ketones, excluding diacetyl, no longer differed significantly from the cellulosic materials. After 24 hours, polyester had the highest mean values for all four ketones. Aldehydes also showed high values for polyester at 24 hours.
Importantly, polyester was not significantly higher than every other material for every compound. For 2-butanone at 24 hours, for example, differences between materials were not statistically clear. Nevertheless, a time-dependent pattern emerged: initially high signals from nylon and wool fell substantially, whereas polyester continued releasing compounds later.
Not all odor compounds behave alike
Even among the ketones, diacetyl was an exception. No significant differences between materials were found at 30 minutes or 3 hours. The authors suggest that its greater tendency to interact with water and cellulose than the other ketones helps explain this difference.
Carboxylic acids also behaved differently from ketones and aldehydes. Signals changed relatively little between 30 minutes and 3 hours, and differences between cellulosic materials and polyester were inconsistent. At 3 hours, wool had the lowest signals for all three acids, with differences from other materials.
The authors discuss how the state of acids in water, and whether yarn bundles are still wet, may also affect the amount entering the air. Even for the same material, uptake and release vary with the properties of the odor compound.
Does cotton favor water while polyester takes up hydrophobic compounds?
One explanation the authors offer for the initially low signals from cellulosic materials is that they may have taken up fewer odor compounds in the first place. Because cellulose readily takes up water, it may preferentially absorb water rather than poorly water-compatible compounds from an aqueous solution such as sweat.
Polyester, by contrast, takes up very little water, and poorly water-compatible ketones and aldehydes are thought to attach readily to its surface. Nylon has both water-compatible and less water-compatible regions, while wool has sites capable of interacting with various molecules. The authors interpreted these differences as contributing to differences in initial uptake and subsequent release.
However, what the experiment directly measured was the signal from compounds released into the air from yarn bundles. It did not extract and measure the entire quantity remaining inside the fibers. Low airborne amounts could reflect either low initial uptake or compounds binding strongly to fibers and not being released. The authors themselves note that compounds retained through binding to materials such as wool may not be released in a form that reaches the nose.
Clues to how airing can reduce odor
Compounds released in large quantities initially became less abundant later. From this finding, the authors proposed that airing might reduce released odor more effectively for wool and nylon than for polyester. They also suggest that if cellulosic clothing smells relatively little after wear, one reason may be its limited initial uptake of hydrophobic compounds transferred through water.
These results do not establish deodorizing effectiveness in actual clothing or determine how long clothes need to be aired. The experiment combined artificial sweat with cleaned yarn bundles; it did not reproduce friction and pressure during wear, fabric structure, microbial production of new odors, or changes after laundering. The artificial sweat was at room temperature, about 20°C, with a pH of 4.3, unlike actual skin temperature and underarm conditions. Nor do the measurements directly reveal perceived odor intensity, pleasantness or unpleasantness, or perfume longevity.
Summary
Sweat odor compounds do not all remain in the same way once they attach to a material. In this experiment, uptake from liquid sweat, release during drying, and binding between compounds and fibers combined to change the picture of different materials between 30 minutes and 24 hours.
The importance of this study is that it considers not just which fiber clothing contains, but which compounds were transferred with water and how. This offers a route toward explaining why cellulosic materials may limit uptake and why release after airing differs between wool or nylon and polyester. Understanding how actual clothes smell will require research connecting these chemical differences with wear conditions and human odor assessments.
References
McQueen, R. H., Eyres, G. T., & Laing, R. M. (2024). Textile sorption and release of odorous volatile organic compounds from a synthetic sweat solution. Textile Research Journal, 94(21–22), 2392–2405. DOI: 10.1177/00405175241249462 / Full original article.
Original article: © The Author(s) 2024. CC BY-NC 4.0.
