 [ Symptoms ] i have a cut on the corner of my mouth that wont heal what can i use to help [ Disease ] if you are referring to a crack in the corner of your mouth where the upper and lower lips join you may be suffering from perleche known medically as angular cheilitis perleche can be caused by a fungal infection in which case you will need to see a doctor for medication to help it heal the condition also can be caused by a deficiency of vitamin b so you can try taking a vitamin supplement assuming you are not allergic to any medications or food colorings or eating more green leafy vegetables which typically contain plenty of different b vitamins because of the possibility this is a fungal infection i would suggest making an appointment with your primary care provider for an evaluation i wish you all the best