Most Likely: Nothing will happen. "You won't get an odor within 8 to 12 hours," says Lucinda Ottusch, lead home economist at the Whirlpool Institute of Fabric Science.

Worst Case: If it's very humid, mildew can develop and create an odor or, over a long period, tiny stains in the clothing. Mildew freckles, left untreated, can start rotting the fabric. To get rid of mildew, soak the clothes in warm or hot water (depending on the care instructions) with a cap of detergent.