First, saliva contains amylase with digestive function. If we chew steamed bread carefully, we will find that steamed bread is sweet, because amylase in saliva breaks down starch in steamed bread into sugar. If you spit frequently, it will inevitably reduce the initial digestion of food in the mouth, thus increasing the burden on the stomach.
Secondly, people secrete about 1-1.5 liters of saliva every day, so a large amount of saliva constantly flows in the mouth, which has the function of washing and lubricating, and can remove food residues and bacteria in the mouth, which is of great significance for preventing infection and dental caries.
Third, mucin in saliva can lubricate mucous membrane and make lips and cheeks move freely.
Fourthly, saliva also contains lysozyme, which can kill some bacteria. Saliva contains mutase and salivary gland corpuscles, which can play an antibacterial role. Saliva also contains secretory immunoglobulin A (S-IgA), which makes it difficult for bacteria to adhere to the tooth surface. So it has an immune effect on dental caries.