The gingival cavity microecosystem , fueled by food residues and saliva, can support the growth of many microorganisms, of which some can be injurious to health. Improper or insufficient oral hygiene can thus lead to many gum and periodontal disorders, including gingivitis or periodontitis, which are major causes for tooth failure. Recent studies have also shown that anabolic steroids are also closely associated with gingival enlargement requiring a gingivectomy for many cases. Gingival recession is when there is an apical movement of the gum margin away from the biting (occlusal) surface.  It may indicate an underlying inflammation such as periodontitis  or pyorrhea ,  a pocket formation, dry mouth  or displacement of the marginal gums away from the tooth by mechanical (such as brushing),  chemical, or surgical means.  Gingival retraction, in turn, may expose the dental neck and leave it vulnerable to the action of external stimuli, and may cause root sensitivity . 
Your mouth guard stays in your mouth fort at least 7 hours in your mouth where it stays in contact with saliva bacteria etc. So is very important you to take care of it or it will cause more damage then it solves
• Clean it every morning with a toothbrush and toothpaste, but you also can use normal soap than rinse it thoroughly.
• Use a adapt container to transport it, so you don’t damage or lose it.
• Check once in a while that it stays intact in time. If it gets perforated, it gets loose or it starts causing discomfort, you should immediately take an appointment with your dentist to repair or replace it.