Mouthguards, like your teeth, should be cleaned regularly. You can brush them, just as you would your teeth, after every use. They can also be rinsed (not soaked) with mouthwash, or cleaned and rinsed with soapy water, a mild bleach solution, hydrogen peroxide or even ordinary denture cleaners. Again, note that you should only rinse your mouthguard with these solutions, not leave them soaking during the day. (Soaking in various cleansers can damage the resins used to manufacture your mouthguard.) Always finish your cleaning by rinsing with ordinary water.
Failing to clean your mouthguard can introduce foreign organisms into your mouth or cause gum recession and tooth decay. The Sacramento Dentistry Group encourages you to brush your teeth at least twice a day and your mouthguard after every use.