An ulcer in the mouth, commonly called a mouth ulcer or canker sore, is a painful sore or lesion that forms on the mucous membrane inside the mouth, such as on the gums, lips, tongue, inner cheeks, or roof of the mouth
. It is characterized by a break or erosion in the delicate tissue lining the mouth, leading to loss of surface tissue and sometimes deeper tissue damage beneath the epithelium
. Mouth ulcers typically appear as round or oval sores with a yellowish, white, or grey center and a red, inflamed border. They can be single or multiple and cause discomfort, especially when eating, drinking, or talking
. The ulcers usually heal on their own within 1 to 2 weeks without treatment, but larger or persistent ulcers may require medical attention
. Common causes of mouth ulcers include minor injury (such as accidentally biting the cheek), irritation from dental appliances, certain foods, infections, stress, hormonal changes, and nutritional deficiencies
. While most mouth ulcers are harmless, a non-healing ulcer could indicate a more serious condition like oral cancer and should be evaluated by a healthcare professional
. In summary, a mouth ulcer is a painful sore inside the mouth caused by tissue breakdown of the mucous membrane, often triggered by injury or other factors, and usually resolves within two weeks
