Leaving freshly washed clothes inside a washing machine for several hours or overnight can cause them to develop an unpleasant smell that may persist even after they are dried.
Experts say the odor is caused not simply by dampness but by the interaction of moisture, bacteria, mold, fabric fibers and microbial buildup inside washing machines.
At room temperature, damp clothes can provide a suitable environment for microorganisms to multiply. Sweat, dead skin cells and natural oils left in fabrics can also provide nutrients for certain bacteria.
A 2021 study in Japan found that the characteristic odor from damp clothes can be caused by chemical compounds released by certain bacteria. Some of these bacteria can withstand drying and ultraviolet exposure, meaning that microorganisms may remain on fabrics even after washing.
The washing machine itself can also contribute to the problem. In front-loading machines, bacteria and dirt can accumulate around the rubber door seal and inside the detergent drawer. If these areas are not cleaned regularly, contaminants can potentially transfer back onto clothes during subsequent wash cycles.
Clothes that remain damp for long periods can also develop mold, which can release compounds associated with a musty, earthy smell.
Fabric type also plays a role. Cotton absorbs more water, while synthetic materials such as polyester and nylon can retain sweat and oils for longer periods. As a result, sportswear and other synthetic garments may retain odors even after repeated washing.
If clothes have developed an unpleasant smell, washing them again is generally recommended. Where fabric-care instructions permit, a warmer wash may help. Soaking clothes in a diluted vinegar solution before washing may also help in some cases, but vinegar should never be mixed with bleach or other chemical cleaners.
The simplest way to prevent odors is to remove clothes from the washing machine soon after the cycle ends. Ideally, they should be taken out within about 30 to 60 minutes and dried in an open, well-ventilated area. Faster drying reduces the moisture available for bacterial and mold growth.
Regularly cleaning the washing machine is also important. The rubber door seal, detergent drawer and other areas should be cleaned periodically, while an appropriate machine-cleaning cycle can help reduce accumulated dirt and microbial buildup.
Cold-water washing can save energy and may help extend the life of some fabrics, but warmer water can be more effective in certain situations for reducing odor-causing microorganisms. The water temperature should always follow the garment’s care instructions.
Removing clothes promptly, drying them thoroughly and keeping the washing machine clean can significantly reduce the risk of unpleasant odors.
