It’s an infection caused by the candida fungus, which is yeast. It can cause diaper rash in infants or vaginal yeast infections in women. The typical symptom of oral thrush is creamy white lesions, usually on your tongue or inner cheeks. If the lesions are rubbed or scraped, it may cause slight bleeding. Oral thrush may spread to the roof of your mouth, your gums or tonsils, or the back of your throat.