Saliva has a number of purposes that make it an extremely useful substance, making it sorely missed when people experience a reduced output. In addition to playing a role in the digestive process, it is also very important for oral health. Some animals have developed additional uses for it. Swifts, for example, have particularly gummy saliva that they used to glue their nests together.
One of saliva's most important roles is as a lubricator. It 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 when trying to eat.
Saliva also contains several enzymes that 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, breaking food down before it reaches the stomach to make it easier to digest. When the enzyme balance 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 that 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 it does have some antibacterial properties, it should not be used like an antibacterial agent, contrary to popular belief, because the mouth is inherently not sterile. Applying it 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.