Candida fungus causes mouth thrush, according to WebMD. Certain medical conditions, medications and stress may trigger abnormal growth of the fungus in the mouth, resulting in thrush.
Conditions that can induce mouth thrush include human immunodeficiency virus infection, cancer, hormonal changes related to pregnancy, diabetes that is not under control and dry mouth, notes WebMD. Corticosteroids, birth control pills and antibiotics are medications that can lead to candida infection. Risk factors for thrush include wearing unfitting dentures and smoking. A breastfeeding mother can acquire the disease from her baby. Signs of mouth thrush include tonsils and bumps in the mouth.