The main thing you need to be careful of when sanitizing your machine with bleach is handling the bleach. You may not be too excited about working with bleach, but know that it's regulated by the U.S. Environmental Protection Agency (EPA), and it's deemed one of the only effective germ killers on the market. When you're diluting the bleach, be sure to wear gloves and work in a well-ventilated area. If you don't have a window or a door to open, wear a face mask that's rated for bleach fumes. You should treat bleach like the chemical that it is. It's caustic, meaning it will corrode metal and burn your skin in its undiluted form. It's also incredibly irritating to eyes, airways and mucus membranes.
It's not a bad idea to get into the habit of cleaning your washing machine once a month, or at least once a season. Top loaders are more prone to build-up because the water sits at one level, whereas the drum of a front-loader turns through the water so they don't tend to get quite as grimy. If you haven't had any major run-ins with germs, you can substitute vinegar for bleach to cut down on your chemical exposure. You can use the cheap white distilled vinegar and mix a solution of half vinegar, half water to keep in a spray bottle and then use a cup of undiluted vinegar to run through your wash cycle.