Xerostomia, or dry mouth, also dry mouth syndrome, is dryness in the mouth. It may be associated with a change in the composition of saliva, reduced salivary flow (also hyposalivation), or dehydration. Causes of hyposalivation include dental caries, oral candidiasis, damage to salivary glands, or certain other causes. Certan Drugs or medications may also cause dry mouth as a side effect.