Oral ulcers are most commonly recurrent aphthous ulcers and are the most common ulcerative damage in the oral mucosa. The prevalence in the population is about 10 to 30%. These ulcers have a cycle of “flare-up-healing-interval” of varying length and have the characteristic of not healing. Oral ulcers have the clinical characteristics of “yellow, red, concave, pain” (i.e., the surface of the lesion is covered with yellow pseudomembrane, surrounded by a congested red halo band, with a central depression and obvious burning pain), and the ulcers start with mucosal congestion and edema, with corn-like red spots and obvious burning pain, followed by the formation of superficial ulcers, round or oval, 5-10 mm in diameter. The mucosal area is further enlarged and whitened, depressions appear, and the pain is further aggravated, sometimes the pain is unbearable and affects eating, and in serious cases it affects normal work and life. This is the most obvious period of ulcer pain, after this stage the pain slowly decreases and the mucosal lesion will be further reduced until the wound heals. The ulcer starts to heal in about 5 to 7 days, when the ulcer surface has granulation tissue formation, the wound surface shrinks, the redness and swelling subsides, and the pain is reduced. The ulcer heals in about 10 to 14 days without leaving a scar. So the ulcer whitening is a stage of ulcer disease progression, the symptoms are the most severe, not aggravated, should be almost healed.