Thick, colourless fluid constantly present in the mouth, composed of water, mucus, proteins, mineral salts, and amylase, an enzyme that breaks down starches. One to two litres are produced daily by the salivary glands. Small amounts are continually discharged into the mouth, but the presence, smell, or even thought of food increases flow. Saliva's main function is to keep the inside of the mouth moist, making speech more fluid, dissolving food molecules for taste, and easing swallowing. It also helps control the body's water balance, since lack of it stimulates thirst when water intake has been low. Saliva reduces dental caries and infection by removing food debris, dead cells, bacteria, and white blood cells.