Question: what is saliva and why do we have it/what is it for?

Susan Cartwright answered on 19 Jun 2015:

Saliva is mostly (99.5%) water. The remaining 0.5% is made up of quite a wide variety of different chemicals, which do a number of different jobs.

First, saliva contains enzymes which start the digestion process. There is a standard school experiment (at least, it was standard in my day!) which demonstrates this: iodine reacts with starch to produce a blue-black colour. If you mix the starch with saliva and keep it warm (body temperature) for a few minutes before adding the iodine, you don’t get the blue-black colour: the saliva has broken down the starch.

Second, saliva contains antibacterial chemicals, which help to protect you from infection caused by bacteria on food or on other things you might put in your mouth.

Third, saliva is important in your sense of taste: it dissolves some of the flavour molecules and carries them to your tastebuds.

Fourth, saliva is simply important as a lubricant, to moisten dry food so that you can swallow it easily. Eating something like toast or crispbread without saliva would be a very uncomfortable experience!