Dishwasher odors are most commonly caused by food particles that build up in the screen at the bottom of the machine over time. The trapped food develops bacterial growth, which leads to unpleasant smells. The odors may also be caused by rotted food scraps that have fallen down into the lower dishwasher tub. Additional causes include garbage disposal blockages and dirty door gaskets.
In most cases, odorous dishwashers can be remedied by locating the source of the odor and removing food particles and build up and by thoroughly cleaning the dishwasher screen with soap and hot water. After the debris has been removed, the next step is to fill a dishwasher-safe cup with baking soda, lemon peels or vinegar. Place the cup on the top rack, and run the dishwasher on a full cleaning cycle without additional dishes.
If the garbage disposal is responsible for the odors, it can be repaired by removing the hose that connects the dishwasher to the disposal and manually removing the debris with a taut piece of wire and a soft cloth. Tough odors can also be removed by filling the detergent tray with a commercial dishwasher sanitizer and running the empty machine through a full wash cycle.