mouth ulcer causes
Less common causes. There are also a number of other, less common causes of mouth ulcers. Some of these are listed below: Herpes simplex infection: a highly contagious virus, also known as the 'cold sore virus', which can cause cold sores on the mouth and the genitals.
If you have recurrent mouth ulcers, they may be caused by an underlying medical condition, such as those outlined below. Vitamin B12 deficiency: vitamin B12 helps to make red blood cells and keeps your body's nervous system healthy. A lack of vitamin B12 can cause tiredness, shortness of breath and mouth ulcers.