Saliva is the fluid of the salivary and oral mucous glands and is used to moisten food, initiate digestion of starches and lubricate the mouth. Typically, it is a tasteless, odorless alkaline fluid composed of 99.5% water. The remaining 0.5% is made of various salts, dissolved gases, enzymes, proteins, urea and other waste products. Much like blood and urine, saliva is employed in clinical laboratory testing by the Food and Drug Administration for conditions such as HIV, and can also be used 'off-label' for hepatitis and cholesterol levels, amongst others.
The production of saliva is stimulated the sympathetic and parasympathetic nervous systems, and a normal human secretes around 1.5 litres every day.
A lack of saliva can be a symptom of many conditions, from anxiety to Sjögren's syndrome.