Towels that smell after they are washed contain bacteria that causes a sour odor, according to Real Simple magazine. The bacteria develops when towels are left in the washer too long or when they are washed in a machine that needs to be disinfected.
An easy way to disinfect a washer and eliminate odor-causing bacteria is to wash a load of whites with bleach prior to washing towels, Real Simple suggests. Towels should be removed from the washer within two hours of the cycle's finish, and they should be dried thoroughly before they are used. Towels that retain a smell should be washed in hot water as part of a small load of only three towels.