Mouth ulcers are caused by a variety of factors, including:

• Injury or trauma to the mouth, such as accidentally biting the inside of the cheek, cuts or burns from hot foods or drinks, sharp teeth, poorly fitting dentures, braces, or rough dental fillings

• Infections , including viral (e.g., herpes simplex virus), bacterial, and fungal infections like oral thrush or hand, foot, and mouth disease

• Irritants and allergies , such as reactions to certain foods (chocolate, citrus fruits, coffee), toothpaste containing sodium lauryl sulfate, mouthwash, or chemicals

• Nutritional deficiencies , especially of vitamin B12, folic acid (B9), iron, and zinc

• Hormonal changes , for example during pregnancy or menstruation

• Stress, tiredness, and emotional factors

• Certain medications , including some nonsteroidal anti-inflammatory drugs (NSAIDs), beta blockers, chemotherapy drugs, and others

• Underlying medical conditions , such as autoimmune diseases, inflammatory bowel disease (Crohn's disease), coeliac disease, oral lichen planus, Behçet's disease, and immune system disorders like HIV or lupus

• Tobacco use , which can irritate the mouth lining and contribute to ulcers

Mouth ulcers that do not heal or recur frequently may indicate more serious conditions, including oral cancer, and should be evaluated by a healthcare professional

. In summary, mouth ulcers arise from a combination of physical injury, infections, irritants, nutritional deficiencies, hormonal and immune factors, medications, and systemic diseases