Saliva has a number of purposes which make it an extremely useful substance, making it sorely missed when people experience reduced salivary output. In addition to playing a role in the digestive process, saliva is also very important for oral health. Some animals have developed additional uses for their saliva. Swifts, for example, have particularly gummy saliva which they used to glue their nests together.

One of saliva's most important roles is as a lubricator. Saliva keeps the mucus membranes of the mouth moist, making them less subject to cracking and discomfort. This fluid also lubricates food in the mouth, making it easier to chew and swallow. As anyone who has experienced dry mouth knows, a mouth without saliva in it can start to feel extremely uncomfortable very quickly, especially if you try to eat.

Saliva also contains several enzymes which perform various functions. The enzyme lysozyme is antibacterial, so it helps to keep levels of oral bacteria at a manageable level. Digestive enzymes like amylase are also present in saliva, breaking food down before it reaches the stomach to make it easier to digest. When the enzyme balance of saliva is disrupted, it can cause health problems, most commonly in the form of a flourishing of bacteria in the mouth.

This substance also has a number of minerals which are regularly deposited on the teeth, helping to keep them healthy and to insulate them from bacteria in the mouth. In some cases, mineral deposits may build up too much, in which case they are known as plaque. The digestive enzymes in saliva also work to dissolve particles of food caught between the teeth, ensuring that they do not rot and compromise oral health.

Although saliva is highly beneficial, it is best kept in the mouth. While saliva has some antibacterial properties, it should not be used like an antibacterial agent, contrary to popular belief, because the mouth is inherently not sterile. Applying saliva to a wound could lead to the introduction of oral bacteria to the bloodstream, and this is not desired. Saliva can also harbor some viruses, which is one of the reasons people are encouraged to avoid kissing sick people.