Whether you buy a used mattress that smells musty or receive an old, musty mattress from a friend, or even if you've stored a mattress in a storage unit or musty basement, you need to clean it and remove the smell. Fortunately, you can clear up the musty smell by absorbing the moisture, disinfecting and freshening the mattress.
Sprinkle a light coating of baking soda over the top and sides of the mattress and let it sit for about three hours. Vacuum the mattress, flip it over and repeat the same process for the bottom side. This treatment not only deodorises the mattress, but also absorbs any moisture that may be causing the musty smell.
Carry your mattress outdoors and place it in direct sunlight.
Fill a spray bottle with white vinegar and mist the mattress with a coat of the white vinegar. Let the mattress sit in the sunlight for three hours, flip it over and repeat on the other side. The vinegar disinfects and deodorises, and the sunlight is a natural cleaning agent as well.