Germs from your clothes may stay in your washing machine and spread to your next load of laundry. If water pools in your machine between loads, germs may breed there, too.
About once a month, to kill germs that lurk, run the machine with nothing in it but chlorine bleach. If the clothes you wash are extra dirty or you live in a hot, humid area, you may want to do it more often.
If your next load of laundry is colors, run the machine empty again, this time with nothing but water, so any leftover bleach won’t ruin your colored clothes.