There is a difference between thrush and mouth ulcers: 1. The cause of onset. The onset of thrush is due to fungal infections, most commonly Candida albicans, while mouth ulcers have nothing to do with fungal infections. The cause of recurrent mouth ulcers is unknown, and can be triggered by factors such as immune deficiency, genetic disorders, endocrine abnormalities and mental stress. 2. Clinical manifestations. The manifestation of thrush is the appearance of white spots on the oral mucosa, which gradually expand and fuse into patches. The white spots adhere tightly and are not easily removed. And the performance of oral ulcers is that red papules or blisters, gradually become round ulcers, surrounded by red color, pain is obvious.