Certain medical conditions can cause mouth ulcers. These can include viral infections such as the cold sore, or herpes simplex virus, chicken pox and hand, foot and mouth disease. Nutrient deficiencies including iron, folic acid and vitamin B12 may also cause ulcers. Other health and lifestyle factors such as extra stress, hormonal changes, quitting smoking or a diet high in spicy or acidic foods may cause mouth ulcers to develop. Talk to your dentist or GP if you have any concerns.