The most common reason for a washing machine to smell like mold is the build up of mold or mildew underneath the rubber gaskets in the machine. This occurs when the rubber gaskets are worn down to the point where moisture leaks behind the gaskets and becomes stagnant. This issue can be easily remedied by replacing the rubber gaskets.
Another common issue is a musty or moldy smell emitting from a front loader washing machine. These machines have gained popularity due to the fact that they are designed to conserve energy. This musty smell is also caused by mildew developing in the rubber gaskets as well as on the rubber door rim. With front loader machines, this can occur whether or not the gaskets are worn.
Mold and mildew can be eliminated from front loader machines by cleaning off the rubber door rim and thoroughly drying it after each use. It is also important for individuals who own front loader machines to use detergent that is specifically designed for front load washing. Additionally, overuse of soap in an energy efficient washer can cause excess residue due to the limited amount of water used each cycle. The residue sticks to the rubber rim and creates a sticky residue with a musty smell.