Stomatitis is mostly caused by dryness, cold, wind and sun in the external environment and imbalance of nutritional elements in the body. Therefore, you can eat more fruits rich in vitamin C, such as kiwi, orange, apple, white pear, grape, dragon fruit, lemon, watermelon and so on. Patients with stomatitis are due to a lack of B vitamins in their bodies, so they should take in appropriate coarse grains, soy products, seafood, meat, milk, animals, liver and other foods. Patients with stomatitis should wear a mask and apply petroleum jelly or lip balm to the corners of their mouths when they go out in the cold winter season. Also, avoid the bad habit of licking the corners of your mouth with your tongue frequently. When yawning or talking, try not to open your mouth wide to avoid tearing the corners of your mouth. If ulcers and yellow pseudomembranes appear at the corners of the mouth, this indicates an accompanying bacterial infection and erythromycin ointment should be applied to reduce inflammation.