Sweat doesn't just stink once—it lingers, seeping into the fibers of clothes and taking hold, sometimes permanently. Even washing clothes on the hot setting doesn't make B.O. molecules go away, it just rearranges them. So, the next time you wear that tank top to Bikram yoga, your body's new moisture activates the trapped microbes from yesterday's workout, allowing them to make a rank reappearance. We've got more on the science of gym clothes stink here, and also made a list of our picks for effective stink-fighting workout clothes.