Mouth sores should be considered as symptoms of serious illnesses. The most common causes of mouth sores include: vitamin and iron deficiency, immune deficiency, physical trauma, Behçet’s disease, and certain foods (acidic foods, vinegar, vinegar-based sauces, salty, spicy, and hot foods, pickles, snacks, and processed foods containing many chemicals), hormonal changes, the stomach bacterium known as Helicobacter pylori, food allergies, stress and anxiety, and smoking.