My cat has a thick mucus that sometimes appears from her mouth. She's been vaccinated, and otherwise is healthy.
How old is your girl?
How long has this been happening? Just in the last few days, or for a few weeks or more?
She's just over a year old. When she was very young, I noticed this a few times--it's a very thick, sticky, grayish mucus. For the last several months, I've not seen this happen with her, and then, last night, she came up to me on our deck, ready to go inside and she had all kinds of things stuck to her mouth-a few bits of birdseed, a little lint, etc., which caught my attention. Her mouth was almost stuck shut! I wiped it all away and she ate and drank normally. It seems to come from right around her "lips." I'm at a loss. It's been very hot, and she spends a lot of the day outside--could this have anything to do with salivary gland problems or something along those lines?
Usually with salivary gland problems, the issue is blockage or swelling rather than overproduction.
There are quite a few causes of increased salivation in cats. Viral infections can cause ulcers in the mouth which can cause drooling, although with your cat being vaccinated, it's a lot less likely. You'd also probably notice your girl being reluctant to eat, due to pain.
Dental disease is another possibility, but less likely in a young cat. Have a look at her teeth just to be sure there's no excessive gum redness or tartar accumulation.
Other causes of mouth ulcers or trauma can lead to salivation - for example, cats may lick something caustic which can burn their tongue. Again, I'd expect less interest in eating with a sore mouth.
Things like esophageal disease or metabolic disease (eg liver disease) can also do it, but I'd expect it to be more consistent, not something that only happens on occasion. Anything that can cause difficulty swallowing can lead to salivation accumulating, but you've mentioned your girl has no trouble eating or drinking after her mouth is cleaned.
It's certainly a puzzle.
What is possible with your girl, given she's young, healthy, with no other symptoms, is that it's either nausea, or she's eating something that really doesn't taste good, which causes hyper salivation in cats.
My suggestion is next time it happens, after cleaning her mouth, see if you can gently open it and have a good look around. If you see any sores or ulcers, get her checked by your vet. If there's nothing there, then you may decide to take her to your vet for a checkup nonetheless. If so, take her as soon as you can during or just after an episode, so he can see what's going on while it's happening.
All the best
16 years experience in small animal practice.