It happens to all of us. After working out and sweating, our clothes don’t smell like when we first took them out of the closet. The mixture of sweat and fabric may cause this change in odor. However, not all smells are the same. There are clothes that we can identify by the pretty foul odor they give off after going to the gym. In fact, a study has just revealed why they smell so bad.
The research. The new paper, a University of Alberta investigation, explains why some commonly used fibers smell worse than others when people sweat. Analyses of several fibers soaked in a solution showed that cotton, viscose, cellulosic, and plant-based fibers, absorbed—and consequently released—smaller amounts of odor-causing compounds than polyester, nylon, and wool.
Mimicking sweat. The team, led by Rachel McQueen, a clothing and textile scientist at the University of Alberta, used a simulated liquid sweat solution to conduct the analysis. “Although we know that polyester is smellier after being worn next to sweaty armpits compared to cotton T-shirts, we haven’t really known why,” she explains. “Now we have a better understanding of how odorants transfer and are selectively absorbed by various fiber types in sweat.”
To do this, the researchers dipped a piece of fabric into a bottle of this simulated sweat solution. They shook it briefly before letting it sit for half an hour. Then, they removed the fabric from the liquid, let it dry, and left again to give the odor particles time to filter out.
Measuring the smell. The next phase of the study was to measure the odor that enveloped the fabric. How? Having each of the researchers smell and rate it didn’t seem to be enough, so the team turned to mass spectrometry, a technique capable of measuring the mass-to-charge ratio of ions in each sample. In essence, it’s a technique capable of detecting odors in the air in real-time.
The team details in the paper that the results showed a clear pattern. Fabrics made from cellulose—natural fibers from plants such as cotton, flax, or hemp—absorbed and released a lower amount of compounds that smelled bad. On the other hand, synthetic fibers like polyester and wool absorbed and released more odors.
Explaining the smell of sweat. As McQueen points out, we have to look at the ingredients that make up sweat to understand why this happens. It’s water, but there are also oily compounds. These compounds are key, as they're where the odor originates. Depending on the chemistry of the fibers, these oils can interact in diverse ways.
“While water-loving cellulosic fibers such as cotton and viscose absorb more of the water from sweat than polyester does, polyester doesn’t want to absorb the water,” McQueen notes. “It’s more oil-loving, and it absorbs more of the odorants, which don’t dissolve in water, and more of the oily compounds, which could also later break down and become smelly.”
The lesser of two evils. The work also divided the odors among the clothes that produced the worst smells. The team found that the smelliest fabrics weren’t the same. The more significant release of odor particles didn’t last as long for nylon and wool. Yes, they smelled at first, but after 24 hours, the odor had dissipated.
“That tells us that while polyester still needs to be washed, for nylon and wool garments, people might be able to freshen them by just airing them out rather than laundering every time,” the lead researcher states. In any case, while most fabrics had at least some redeeming qualities in terms of odor, there was one clear loser in the smell test: polyester. Interestingly, it’s one of the cheapest fabrics on the market, much more affordable than cotton or linen.
Final tip. For all these reasons, the researchers suggest that anyone who regularly exercises (or sweats a lot daily) should avoid polyester clothing as much as possible: “Even with some of the anti-odor claims on some clothing labels, you might want to be cautious. If the anti-odor property is due to an antimicrobial, it may not be as effective as you think because there’s another mechanism in play, which is all about the fiber chemistry and the interaction with odorants,” McQueen concludes.
We already knew that the fabric of our clothes was crucial when it comes to dealing with heat, as well as which one was the best. Now, this study illuminated us on which fabric gives off the worst odor. As such, if you sweat more than normal, you'll now know what to avoid.
This article was written by Miguel Jorge and originally published in Spanish on Xataka.
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