It's best to leave the dishwasher door open for a while after running a program, as closing it creates a warm, moist environment that's very comfortable for mould and other microbes. However, if you already have mould, you can use bleach to remove it. Another consequence of this hot and humid environment can be unpleasant odours. This can be remedied by sprinkling a small amount of baking soda before running a cycle.