Mouth sores should be considered as symptoms of serious illness. The most common causes of mouth sores are: Vitamin and iron deficiency, immune deficiency, physical trauma, Behçet's disease, foods (acid foods, vinegar, vinegar sauces, salty, spicy, spicy foods, pickles, snacks and prepared foods containing many chemicals), hormone changes, stomach microbe known as Helicobacter Pylori  , food allergies, stress and anxiety, smoking.

 

Source: http://www.kbb.org.tr