Although some cases of dry mouth are naturally occurring, most cases are caused by one of these factors; prescription medications (usually prescribed for high blood pressure or depression) antihistamines, adult beverages, and mouthwashes with alcohol in them. (see "Why Regular Products Don't Work") When your mouth is dryer, you have less Saliva. Saliva naturally contains Oxygen, which keeps your mouth healthy and fresh. These bacteria are anaerobic, which simply means that they will thrive and make more sulfur in the presence of little or no oxygen. Thus if you have less Saliva, you have less oxygen, thereby creating an anaerobic environment, perfect for the bacteria to produce more of these odorous and sour/bitter compounds. When your mouth is dryer, you have less Saliva. Saliva naturally contains Oxygen, which keeps your mouth healthy and fresh. These bacteria are anaerobic, which simply means that they will thrive and make more sulfur in the presence of little or no oxygen. Thus if you have less Saliva, you have less oxygen, thereby creating an anaerobic environment, perfect for the bacteria to produce more of these odorous and sour/bitter compounds.