The white part inside or on the surface of the mouth ulcer lesion is a combination of pus, necrotic material and exuded cellulose. 1. When oral ulcers begin to attack, the permeability of capillaries is significantly increased, and a large amount of inflammatory fluid is exuded, making the surface of the ulcer red and swollen. Subsequently, necrotic cells cover the surface of the ulcer, forming a yellowish-white pseudomembrane. 2. Oral ulcer is the mucous membrane or skin surface layer necrosis and shedding to form a depression for ulcers. Fibrous tissue grows into a large number of capillaries, through the blood circulation, the epidermis is full of bright red. After the loss of vitality of the senescent cells completely off, the ulcer epidermis and the normal mucous membrane color consistent with a light pink. 3. According to the degree of its destruction of tissue, can be divided into shallow ulcers and deep ulcers. Superficial ulcers only destroy the epithelial layer and leave no scar after healing, such as recurrent aphthous ulcers. Deep ulcers, on the other hand, involve the submucosal layer. Scarring remains after healing. Such as recurrent necrotizing peri-mucosal glandular inflammation. The appearance of mouth ulcers should be timely medical treatment, follow the doctor’s instructions for examination, clear the cause of the disease and follow the doctor’s instructions for treatment.