Do all humans drool when they sleep?
I would have to say it probably varies from person to person.
I assume that I personally don’t, if I do, it is very infrequently, simply because my pillow never has any marks on it to suggest I do.
Plus I never wake up with my face on a wet spot.
In my experience, people are much more prone to drooling while napping during the day than at night. Furthermore, I would guess that salivary glands are responsible-most people don’t turn in right after dinner and I’d guess that the glands are less active at night.
I’ve noticed I usually drool more when my nose is stuffy. I’d assume all humans drool (produce saliva) when they sleep, but whether or not it ends up on their pillow, sheets, hair, SO - depends on the angle of their head and whether or not they sleep with their mouths open.