Oral thrush results from an overgrowth of a species of yeast called Candida albicans, says About Health. Typical causes in adults include untreated diabetes, HIV, chronic dry mouth, ill-fitting dentures and cancer, states WebMD. Long-term use of antibiotics, steroids or birth control pills also potentially causes oral thrush.
Oral thrush, or oral candidiasis, affects men, women, children and infants, says WebMD. Candida is the same yeast that causes diaper rash in babies and vaginal yeast infections in adult women.
Small amounts of candida yeast are naturally present in the human body, reports WebMD. When an overgrowth of this yeast occurs in the mouth, symptoms include yellow or white lesions on the tongue, inner cheek and roof of the mouth. Severe oral thrush often makes it difficult to swallow and sometimes causes a high fever.