The yellowing of gum ulcers may be caused by drug pigmentation, oral ulcer pseudomembrane, and suppuration caused by apical inflammation. 1. Drug pigmentation: patients who use topical drugs for ulcers, after a long time of accumulation, the pigment will be deposited in the ulcers, resulting in yellowing of the ulcers. 2. Oral ulcer pseudomembrane: oral ulcers are usually covered with a layer of yellow pus moss on the ulcer surface, also known as oral ulcer pseudomembrane. 3. Pus caused by apical inflammation: Pus caused by apical inflammation will lead to the appearance of yellow sticky pus in the gums, resulting in the phenomenon of yellowing of the ulcers. It is recommended that patients always observe their own situation, go to the hospital in a timely manner under the guidance of the doctor’s treatment, and maintain oral hygiene, rinse after meals and brush your teeth every day.