Clinicians may encounter symptoms of xerostomia, commonly called “dry mouth, ” among patients who take medications, have certain connective tissue or immunological disorders or have been treated with radiation therapy. When xerostomia is the result of a reduction in salivary flow, significant oral complications can occur. Terminology of xerostomia is widely includes one of the symptoms of Sjögren's syndrome (SS) and also accepted as dry mouth included senile xerostomia among geriatric patients due to salivary dysfunction which differ from thirst as the result of hypovolemia according to Asagawa's definition in 1976. Xerostmia and keratoconjunctivitis sicca commonly complicated, lymphocyte infiltration in excretion salivary, larcimal, and sweat glands in Sjögren's syndrome. Senile patients often complaints dryness of the mouth because some drugs related to hypertensives and may occur as a side effect of medications. Classification of this disorder based on each causes is so useful to understand the pathogenesis and attribute to the treatment closed in the future. This review considers the changes in salivary glands associated with ageing and concludes that there is no evidence to show that xerostomia is likely to result from the ageing process alone. The four main factors causing xerostomia are presented as factors affecting the salivary center, factors affecting the autonomic outflow pathway, factors affecting the salivary gland function, and factors producing changes in fluid or electrolyte balance. It can be often seen that the condition is a side-effect of diseases and the drugs used to treat these diseases. Xerostomia often develops when the amount of saliva that bathes the oral mucous membranes is reduced. However, symptoms may occur without a measurable reduction in salivary gland output. The most frequently reported cause of xerostomia is the use of xerostomic medications. A number of commonly prescribed drugs with a variety of pharmacological activities have been found to produce xerostomia as a side effect. Additionally, xerostomia often is associated with Sjögren's syndrome, a condition that involves dry mouth and dry eyes and that may be accompanied by rheumatoid arthritis or a related connective tissue disease. Xerostomia is an uncomfortable condition and a common oral complaint for which patients may seek relief. Complications of xerostomia include oral mucositis, candidiasis or difficulty of swallowing of dry foods such as bread without water. We need to identify the possible causes and provide the patient with appropriate treatment in order to make proper classification of this disorder.