A person suffering from xerostomia experiences a significant reduction in salivary secretion, which impairs the natural cleansing action of saliva. Saliva plays a critical role in buffering oral acids, remineralizing enamel, and inhibiting bacterial growth. Without adequate saliva, the oral environment becomes more acidic and favorable for cariogenic bacteria, leading to an increased risk of dental caries. Therefore, xerostomia directly contributes to a rise in the incidence of dental decay.

Reference: Oral Pathology, Neville, 4th Edition.