Why Is Milk White?: & 200 Other Curious Chemistry Questions (2013)
4. Health and Safety
What are the chemicals in spit?
Mostly water. About 98 percent water, in fact. Saliva also contains dissolved salts, mucus, some antibacterial molecules, and enzymes such as amylase, which breaks down starch into simple sugars. Another enzyme, lipase, breaks down fat. So saliva is actually the first step in the digestive process.
Antibacterial agents such as peroxidase, immunoglobulins, lysozyme (an enzyme that breaks open bacterial cell walls), and lactoferrin (a protein that kills bacteria and fungi) are produced in saliva.
Saliva in mice includes a hormone called nerve growth factor, which helps healing when they lick their wounds. It is not a component of human saliva, however.