Does it smell like mildew? That means it’s growing enough mold to cause an allergic reaction. So get that towel into a washing machine, on hot with bleach, before you use it again. And when you shower, crack a window or turn on a vent. Moisture is fodder for mold, fungi and bacteria. But according to the University of Arizona, you can kill 90% of mold and bacteria in your bathroom simply by drying it out.