I get this all the time. This last time I did some searching and found out it is caused by a vitamin B deficiency and/or a fungus. I have tried just about everything in the past including hydrocortisone cream and expensive OTC Herpes balms. Nothing seemed to help and it took weeks for it to go away. This time I tried Lamisil cream (Lamisil does not claim it is for this use). It's for Athletes Foot (which is also a fungus) and it worked great. Please be very careful not to get it inside your mouth.