I have this same scenario but it was not listerine. Another whitening product which included prewhitening rinse. It seems that the salivary gland is irritated. Based on these other cases I am almost positive that it is irritation from the product. I don't have much pain at all just a little soreness. Will the swelling go away on its on?
What did you do about it ?
Been using Whitening Listering too... 30 second rince; (The stuff was too strong for a 60 second rince) morning and before going to bed. On the 3rd morning, a somewhat huge lump appreared at the bottom part of my left jaw, right above the neck. The sensation of having chewed on a sour candy is omnipresent. Obviously, it hurts a little when I rub this region with my fingers.
I used advil to reduce the size of the lump without result.
My supposition is that the product severely iritated either the salivary gland or jaw muscle during the night. The fact that there is no jaw movement during the night confined the product to a specific part of the back mouth...
I hope the swelling will go away by itself?