Why does dirty laundry stink?

Anyone who has ever tried to stretch a T-shirt or a pair of pants one day too many knows that nose-pinching, eye-watering, neck-twisting dirty clothes smell. But what causes it?

Behind that acrid odor is a half dozen chemicals known as volatile organic compounds (VOCs), “generated by the action of microorganisms in breaking down the components of sweat, human skin cells and secretion substances from the glands,” the authors write in a new study published in the Journal of Chromatography A. Knowing what causes laundry to smell so badly can assist with the development of the most effective and ecologically friendly cleaning agents possible.

To track down what exactly causes foul odors in clothes, Northumbria University researchers first provided a handful of volunteers with a new pair of socks. Each participant wore the socks for at least 10 hours. A separate cohort of individuals were given T-shirts to sport for two to three hours while participating in a soccer tournament. After completing the predetermined period of wear, volunteers bagged clothing samples for later analysis.

In order to gauge the degree to which each item emitted a foul odor, the researchers actually sniffed and graded each article of clothing on a scale of zero to 10, with the low end of the spectrum indicating no odor and the higher end representing a strong, unpleasant smell.

To determine the chemicals present on the T-shirts and socks, samples were taken from each one. Items were then washed on a cold cycle using unscented detergent, and resampled before they were dried, at which point researchers took one final series of specimens.

Following an analysis using a mouthful of a method called static headspace – multi-capillary column – gas chromatography – ion mobility spectrometry (SHS-MCC-GC-IMS), six main VOCs were identified as the main culprits behind smelly clothing. Each one left its own scented signature. Butyric acid, for example, produced a rancid butter-like odor, while 2-heptanone created a banana-like fruity smell, the researchers found.

The concentration of VOCs on the once soiled clothes decreased but were not totally gone after washing. While researchers have yet to determine the optimal settings to eliminate unwanted smells, singling out the odor-inducing VOCs lays the groundwork for future studies to analyze the effectiveness of different washing processes.

That clean laundry smell often comes at a cost to the environment and could even pose a danger to human health, previous research has found. A 2008 study out of the University of Washington, for example, determined that many top-selling laundry products and air freshener emit dozens of different chemicals. In fact, of all six products tested that year, every single one turned up positive for a chemical regulated by federal law as toxic or hazardous.

Having a steady supply of clean clothes is important. No one wants to start their day off smelling like they spent the night in a locker room. But if we have a better understanding of what exactly we’re trying to scrub away, keeping our clothing clean doesn’t have to been such so dirty for the environment.

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