What is dry mouth? Dry mouth, or xerostomia, affects many people for many reasons. Saliva is important because it helps us chew, speak, and swallow. It also helps to flush bacteria away from the teeth and without an adequate amount of saliva the risk for dental decay increases.   There are many reasons a person can have dry mouth. Certain medications, how you breathe at night, systemic diseases (such as diabetes), cancer treatments, salivary tumors, or salivary stones can...