Chuck is absolutely right.
That warm,damp atmosphere after your wash is an ideal breeding ground for bacteria, and will eventually cause black mould to develop on the door seal.
I do the boil cycle as Chuck says monthly, use the cheapest biological powder I can find. It must be powder.
This is an ideal time to get that drawer out and give it a very good wash, and the drawer cavity. I find a bottle brush to be ideal for cleaning as far back as possible and the roof.
While your at it, use a suitable implement to clear the jets in the roof where the water comes out. I use a cable tie because it is flexible to get in the hole, and strong enough not to break.
This is a very good site indeed for all your white goods problems:
http://www.ukwhitegoods.co.uk/modules.php?name =Content&pa=showpage&pid=43