Lip leaking - worst habit ever!
My DD did this last winter right around her 4th birthday. It started while she had a bad cold and a runny nose but continued for a long time even after her cold was gone. I tried so many things without success, including leaving it alone. Sometimes I would wash the area and put antibiotic cream on it and bandages at bedtime and it would look so much better in the morning, and then she would come back from preschool with it all raw again. I tried keeping it covered during the day but she would lick under the bandages. I finally had success with thick lines of zinc-based sunscreen; I used Badger. I put it on as often as I could during the day, and at night. She did not lick through the Badger (I put it on really thick), which allowed her face to heal. And yes, the sunscreen looked ridiculous and got all over everything. It was enough to help her break the habit and we were able to stop it once the winter ended and the air got moister again. She started doing it again this winter but luckily the sunblock was able to help again. I also let her chew gum, which keeps her mouth otherwise occupied. Good luck!