Mouth ulcers appear as small round lesions (or sores) in the oral cavity (mouth). Generally the lesions are red, white or grey in colour. In medical term, these are also known as apthous ulcers. Mouth ulcers are usually not very painful. The sizes of such ulcers vary and so the time of healing. The proper cause for the manifestation of moth ulcers is not known but factors like stress, smoking and tissue damage may augment the chances of such ulcers. In addition to that intake of some fruits (citrus fruits) and vegetables may worsen the condition. Dental problems (sharp tooth or braces) may also lead to mouth ulcers. In pathological states like malnutrition, vitamin and iron deficiency and gastrointestinal disease mouth ulcers are also visible. Generally, the ulcers subside automatically but in some cases specific treatment is recommended.