Stomatitis

Stomatitis is an inflammation of the mucous lining of any of the structures in the mouth, which may involve the cheeks, gums, tongue, lips, throat, and roof or floor of the mouth. The inflammation can be caused by conditions in the mouth itself, such as poor oral hygiene, poorly fitted dentures, or from mouth burns from hot food or drinks, or by conditions that affect the entire body, such as medications, allergic reactions, radiation therapy, or infections.

Pathophysiology
Severe iron deficiency anemia can lead to stomatitis. Iron is necessary for the upregulation of transcriptional elements for cell replication and repair. Lack of iron can cause the genetic downregulation of these elements, leading to ineffective repair and regeneration of epithelial cells, especially in the mouth and lips.

When it also involves an inflammation of the gingiva, it is called gingivostomatitis.
Angular stomatitis

Irritation and fissuring in the corners of the lips is termed angular stomatitis or angular cheilitis. In children a frequent cause is repeated lip-licking and in adults it may be a sign of underlying iron deficiency anemia, or vitamin B deficiencies (e.g. B2-riboflavin, B9-folate or B12-cobalamins), which in turn may be evidence of poor diets or malnutrition (e.g. celiac disease).