Towels that aren't properly dried after use are likely to grow mold. For example, wet towels tossed into hampers, kept in a zipped gym bag, left in a pile on the floor or left in your washing machine can easily grow mold. Towels that are hung too closely or don't get enough air ventilation may also become smelly and moldy.
Washing towels in hot water will usually remove musty smells. If your towels have visible mold growth, which typically appears in spots, brush off the mold outside before washing. Adding chlorine bleach to the washer according to label instructions will kill mold and sanitize your towels, but it might also bleach or discolor them. If towels are extremely moldy, consider discarding them.
Prevent mold growth in towels by letting them dry completely between use. Hang up wet towels promptly and don't leave wet towels in the hamper or in other enclosed spaces. Run the bathroom fan during and after your shower to help remove moisture from the air, and consider installing a dehumidifier. If your bathroom is very humid, consider drying bath towels elsewhere, such as in the garage.
Mold can also grow in your washing machine or dryer, which may cause your towels and clothes to smell. If your washer or dryer smells musty, consult your owner's manual for instructions on removing mold. For example, running an empty load with a cup of bleach can help kill mold. Prevent mold in your washer and dryer by only using the recommended amount of detergent, using high-efficiency detergent in high-efficiency washers and leaving the washer and dryer doors open after use to dry.