I honestly have no idea how the dark corners developed because after I developed the peeling lips problem last year, I made sure to stop licking my lips. I just had a test done and results are normal. I'm suspecting this is what people say when doctors are useless in this sense. I'm going to a derm tomorrow but I expect the same.
They get a little worse when the skin overgrows again, especially when they get wet but this is the "best" they can look for now. I don't know what else I can do as it seems to me that if I apply something else it could make things a lot worse.