Think about all of the bacteria, food, and germs we have in our mouths. Now think about how all of those germs and bacteria latch onto our toothbrushes. Plus, if you don't close the toilet lid when you flush, microorganisms can scatter all over your bathroom, often landing on surfaces like your toothbrushes.
Rinsing your toothbrush after every use is not the best way to keep it clean, so you should be soaking it in hydrogen peroxide or an antibacterial mouth wash every so often. It's also important to let it dry out after every use, so don't keep it in a container, as this encourages more bacteria to grow. Replace your toothbrush every three or four months. Your toothbrush holder can be pretty gross by association, so you can run it through the dishwasher once in a while to get the gunk out.
