Is the white substance in a mouth ulcer pus?

The white substance on the surface of a mouth ulcer is usually not pus, but rather composed of necrotic material from the oral surface. The appearance of this white substance often indicates that the mouth ulcer is entering the healing stage and is a sign of improvement. Specifically, the causes of mouth ulcers are complex and may be related to various factors such as diet, trauma, immunity, and mental stress. During the healing process, due to the resolution of local inflammation and tissue repair, a white pseudomembrane may form over the ulcer surface. It should be noted that if the mouth ulcer is accompanied by significant pain, redness and swelling, fever, or other symptoms, or if the white substance changes color, such as turning yellow or green, it may suggest a risk of infection or suppuration. In such cases, timely medical attention should be sought, and targeted treatment should be carried out under the guidance of a physician to prevent worsening of the condition.