Oral ulcers are most commonly recurrent aphthous ulcers, which are generally clinically classified into mild aphthous ulcers, heavy aphthous ulcers and herpes-like aphthous ulcers according to the differences in symptom presentation. Mild aphthous ulcers: the most common, the ulcer surface is small and few in number, isolated and scattered, sub-circular, and generally with clear borders. It occurs in the lip and cheek mucosa. When an ulcer develops, there is a peripheral congested band covered with a yellow pseudomembrane, and the ulcer is centrally depressed with a distinct burning sensation. Recurrence is regular and is generally divided into an attack phase, a healing phase, and an intermittent phase. Severe aphthous ulcers: The ulcer is large and deep, occurring singly, like a “crater” with a raised periphery, but the edges remain neat and clear. They begin in the corners of the mouth and progress to the parapharynx and soft palate, where they can interfere with vocalization and swallowing functions. These ulcers are often accompanied by systemic symptoms such as fever and malaise. The ulcer lasts for a long time and leaves a scar after healing. Herpes-like aphthous ulcers: The ulcers are small and numerous and are located anywhere in the mouth. Adjacent ulcer surfaces may fuse to form a sheet. When herpes-like ulcers occur, saliva secretion in the mouth increases and may be accompanied by general discomfort, headache, and low fever. Herpes-like ulcers do not leave a scar after healing.