As a NYC Cosmetic Dentist, I get asked about saliva quite a bit (often when I have instruments in someone's mouth and they start to drool.)
So let's answer the common questions: What is saliva? Where does it come from? What's in it? What is it used for? What are we still learning about it?
What is saliva, and where does it come from?
Call it what you want -- spit, spittle, drool, etc -- saliva is one of the most common (and obvious) bodily fluids. It's the watery substance that's prevalent in everyone's mouth, and is produced by three pairs of major salivary glands (and many, many minor glands).
These three major glands are located on the inside of each cheek, on the bottom of the mouth, and under the jaw, towards the front of the mouth. The rest of the minor glands are all over the rest of the mouth (the palate, the tongue, your lips, etc.)
These glands work together to produce saliva all day, every day (although production of saliva dramatically falls during sleep. Hey, that's why your mouth is so dry when waking up!) In general terms, most healthy humans will produce somewhere between one and two quarts of saliva a day.
What is in saliva?
This may be a surprise to some people, but Saliva is 98 percent water. Although if you think about it, maybe it's not so surprising -- we learned way back in science class that our bodies are mostly water, so is it a reach that the clear fluid we produce is mostly water? Not really.
But the other 2 percent is the important part. That other 2 percent is a combination of mucus, enzymes (mostly amylase, lysozyme, lingual lipase), electrolytes (sodium, potassium, calcium, etc), and antibacterial compounds. Recent research on mice has centered on the painkiller Opiorphin, which is also present in saliva (Opiorphin is said to be stronger than Morphine). More on this below.
What is saliva used for?
Saliva has several important uses. To start, it's the first step in digestion: the enzymes in saliva begin to break down food, and the watery consistency of it helps moisten food, making it easier to swallow. Of course, this is why your mouth waters when you see/smell good food. And we've all heard of Pavlov's dog, where he conditioned the dog to salivate by ringing a bell (that promised food).
So yes, saliva is used in digestion. But it has other uses as well: for example, saliva is an important component in keeping the mouth (and teeth) clean. Yes, you still need to brush and floss, but that constant water action in your mouth plays an important role in oral hygiene by washing away stray food particles.
Saliva also has an important role in protecting the mouth, lips and gums. It's a sticky coating that protects these otherwise tender areas. Indeed, it's not going to keep you from getting cuts, etc., but saliva certainly prevents countless minor abrasions to these exposed areas.
Saliva also assists your taste buds in doing their job by trapping the thiols that are produced from food compounds. Bet you didn't know that.
Like I mentioned earlier, the painkilling effects of saliva are being studied. We know animals "lick their wounds," and the finding of Opiorphin in saliva suggests that might have more bearing than we first thought. We know from our own experiences that this phenomenon is not so in humans, but as of this writing, the research is still ongoing.
Of course, there are topical uses of saliva as well, such as a woman seductively licking her lips, or perhaps young boys having spitting contests. And baseball players -- need I say more? OK, maybe these aren't scientific uses or such, but I'd be remiss if I didn't mention them as well.
So as you can see, saliva has a wide variety of uses, some of which we are still discovering to this day.
What is left to be discovered?
In researching this article, the most interesting new development I found is the Opiorphin work. In simple terms, research suggests that mice/rats indeed benefit from this as a painkiller. There's still quite a ways to go on this angle, but it's definitely worth mentioning here. I'm not sure if we'll ever get to the point where our own saliva is a painkiller, but then again, it is something "new" in a fairly well-known substance.
So there you have it - a basic primer on saliva, with some new research thrown in. Aren't you glad you weren't afraid to ask about it?
Until next time, keep smiling!