DefinitionVarious types of sores can appear anywhere within the mouth, including the inner cheeks, gums, tongue, lips, or palate. Alternative NamesAphthous stomatitisCommon CausesMost mouth sores are cold sores (also called fever blisters), canker sores, or other irritation caused by:Biting your cheek, tongue, or lipChewing tobaccoBracesA sharp or broken tooth or poorly fitting denturesBurning your mouth from hot food or drinksCold sores are caused by herpes simplex virus and are very contagious. Usually, you have tenderness, tingling, or burning before the actual sore appears. Herpes sores usually begin as blisters and then crust over.The herpes virus can reside in your body for years, appearing as a mouth sore only when something provokes it. Such circumstances may include another illnes