I understand it can be thicker for someone who isn’t hydrated enough. This question strictly refers to a healthy well hydrated individual.
Bonus question- what governs saliva to sometimes have bubbles and sometimes don’t?
In: Biology
Saliva is mostly water, but it also has other things like mucus mixed in with the salivary glands. That mixed-in mucus makes saliva thicker. When you’re dehydrated, you have less water available to add to saliva, so it ends up as relatively more mucus, which makes it thicker.
As for bubbles – I’m not certain, but I think that’s because there’s air in your mouth. Even when your mouth is closed, the air that you’re breathing through your nose goes down your throat, which connects with your mouth. If you focus as you take a deep breath through your nose, you can probably feel the air move along the top of your mouth.
Since air and saliva are in your mouth, the two are mixing together as you move your tongue (like when you’re swallowing). When air mixes with any liquid, it wants to rise out of the liquid because the air is less dense. However, the surface tension of the liquid (how much the surface of the liquid wants to stay smooth) determines whether the air can break the surface of the liquid. Water has high surface tension and wants to remain smooth, so the air will break the surface and not form a permanent bubble. Adding things to water (like soap) lowers the surface tension so that bubbles stay at the surface longer. I think the proteins in the mucus make saliva’s surface tension low enough that small bubbles can exist long enough to be visible.
Because it has stuff other than water in it. A whole bunch of electrolytes and importantly mucus, proteins and amino acids which have a variety of functions but also contribute to the viscosity significantly.
Re: bubbles. Not sure what you mean but it’s not coming out of your glands all bubbly, that would be down to what you’re doing with your mouth and how viscous and able to hold bubbles it is.
Proteins: mucus is a principal protein chain (“polymer”) that can alter the thickness (“viscosity”) of saliva
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