There are nearly 332,000 genetically distinct bacteria on the human hand. You may not think of it like this, but germs are transported to your body via your mouthguard everytime you touch it. Throw a sickness in the mix and your dirty mouthguard will make sure you stay in bed all season.
Your mouthguard provides the ultimate habitat for bacteria. Germs thrive best in warm, dark and moist environments...like where your mouthguard lives: in your sports bag, sports bra or even your sock. This is why it's important to learn how to clean a mouthguard and store it properly. 
Using a non-abrasive toothpaste and a soft bristle toothbrush, give your mouthguard a good brush then rinse.
Disinfect thoroughly using 3% hydrogen peroxide. Flush or soak the guard with the solution for no more than 10 minutes.
Simply washing your mouth guard with anti-bacterial soap will help keep bacteria at bay.
There are non-alcohol based cleaners that are specifically formulated for cleaning your mouthguard. You can easily sanitized your guard with one soak.
Don't throw your mouthguard in your practice bag with your cleats and sweaty socks. When you're done with your mouthguard, store it in a ventilated case.
The less often you have to use your hands to remove the guard, the smaller chance you have of getting sick from the bacteria. If find yourself removing your mouthguard every time you need to talk or drink, consider getting a custom fit mouthguard.
If you already have a SISU or a custom fit mouthguard and you still find yourself taking it out to drink or talk, check your fit. You might need an adjustment or remold.
At the very least...give your mouthguard a rinse with your water bottle before putting it in your mouth.
Soak your guard overnight
Use isopropyl (Rubbing) alcohol or alcohol based cleaning agents.
Use hand sanitizer, dish soap, Bleach or Denture Tablets
Put it in the dishwasher
