The main reasons for getting recurring canker sores include:

• Emotional stress and hormonal changes, such as during menstrual cycles
• Minor mouth injuries from biting the cheek, dental work, or rough teeth cleaning
• Dietary deficiencies, especially in vitamin B-12, zinc, folic acid, or iron
• Sensitivity or allergies to certain foods like chocolate, coffee, strawberries, eggs, nuts, cheese, spicy or acidic foods
• Use of toothpaste containing sodium lauryl sulfate
• Some underlying medical conditions affecting immune function, like inflammatory bowel diseases, Behçet's disease, or HIV/AIDS
• Genetics, with some people more prone to canker sores running in families

Canker sores are not contagious and tend to heal on their own within 7 to 10 days, but they can be painful while eating or talking. Reducing triggers like stress, avoiding irritant foods, maintaining good oral hygiene with a soft toothbrush, and addressing vitamin deficiencies can help reduce their frequency and severity. If canker sores persist for more than two weeks or are very severe, it is advisable to see a healthcare provider for further evaluation and treatment options.