Why does laundry get smelly if it stays wet? A textile scientist explains how to fix it

You forget a load in the machine overnight, and by morning it smells worse than before you washed it. The science-journalism coverage adds useful context, while the strongest evidential footing still comes from the underlying data, papers or institutional documentation.

That matters because chemistry gains force when a claimed structure or process can be described with enough precision to be reproduced by others. Synthetic routes, spectroscopic signatures, yield under defined conditions and stability under realistic operating parameters are the currency of credibility in chemistry, and a result that lacks these details cannot be evaluated independently. The distance between a discovery on a laboratory bench and a process that works reliably at scale is measured in years of optimization, and each step reveals constraints that were invisible at smaller scale. This article has been reviewed according to Science X's editorial process and policies. The answers lie in both biology and textile science, which help explain why some fabrics are affected more severely than others.

A Japanese study in 2012 traced the smell to a compound this bacterium produces. A 2025 study found household washing machines themselves host persistent microbial biofilms (colonies that detergent alone struggles to remove), especially around door seals and.

Each cycle, that biofilm can reinoculate freshly washed laundry, so clothes can emerge from a "clean" wash already carrying the seeds of the smell. A recent Canadian study modeled how odor compounds migrate from sweat into fibers, confirming polyester retains substantially more of them than cotton or viscose.

Research on moisture-repelling textiles has found that with all those oils trapped in the polyester, bacteria have a field day feasting on them. Discover the latest in science, tech, and space with over 100, 000 subscribers who rely on Phys. org for daily insights.

The broader interest lies in whether the claimed property or reaction pathway can be characterized with enough precision to support replication by other groups. Chemistry has a replication problem that is less discussed than the one in psychology or medicine, but it is real: synthetic procedures that work reliably in one laboratory sometimes fail to transfer, for reasons ranging from impure starting materials to undocumented temperature sensitivities. A result that comes with full experimental detail and a clear characterization of the product is far more valuable than one that reports a discovery without the procedural backbone.

If you accidentally end up with a smelly load of laundry, the only way to fix it is to wash it again, preferably at the hottest temperature possible. Move laundry from the washer to the dryer or clothesline within roughly 30, 60 minutes.

Because this item comes through Phys. org Chemistry as science journalism, it should be treated as contextual reporting rather than primary evidence. Good science reporting can identify why a result matters, connect it to the wider literature and make technical work readable, but the decisive evidence remains in the original paper, dataset, mission release or technical record. That distinction is especially important when a story is later repeated by aggregators, because repetition increases visibility, not evidential strength.

The next step is to see whether independent groups working with orthogonal techniques reach compatible conclusions, and whether the result scales beyond the conditions used in the original study. Chemical discoveries that matter tend to be ones whose key properties can be measured by multiple spectroscopic, crystallographic or computational methods that are unlikely to share the same blind spots. Scalability, cost and long-term stability under realistic operating conditions are additional filters that come into play before any practical application becomes viable.

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