White Shark
You wrote:
"I have reason to believe it's my retainers"
If it is your retainers, it may be more related to the material they are made of, less to bacteria.
If your lips improve, you are most likely allergic to something your retainers are made of or maybe a product you use to wash it.
If I were you, I WOULD NOT USE LISTERINE!
Unless you want to develop a new allergy to something in LISTERINE! If that is your goal, go on!
WS