You pull a load out of the machine, and something is off. The clothes are technically clean, but there’s a faint musty, damp-towel funk that no amount of fabric softener quite covers. Lean in toward the machine itself and you might catch it there too, hanging around the rubber door seal. It’s tempting to blame a bad rinse. The more accurate answer is ecology: your washing machine is a living habitat, and over time it can hand its own microbes off to everything you wash.