Oral thrush is a condition in which the fungus Candida albicans accumulates on the lining of your mouth. Candida is a normal organism in your mouth, but sometimes it can overgrow and cause symptoms.
Oral thrush causes creamy white lesions, usually on your tongue or inner cheeks. Sometimes oral thrush may spread to the roof of your mouth, your gums or tonsils, or the back of your throat.
You may have an increased risk of oral thrush infection if any of these issues apply:
Weakened immunity: Oral thrush is more likely to occur in infants and older adults due to reduced immunity. Some medical conditions and treatments can suppress your immune system, such as cancer and its treatments, organ transplantation and required drugs that suppress the immune system, and HIV/AIDS.
Diabetes: If you have untreated diabetes or the disease isn’t well-controlled, your saliva may contain large amounts of sugar, which encourages the growth of candida.
Vaginal yeast infections: Vaginal yeast infections are caused by the same fungus that causes oral thrush. You can pass the infection to your baby.
Medications: Drugs such as prednisone, inhaled corticosteroids, or antibiotics that disturb the natural balance of microorganisms in your body can increase your risk of oral thrush.
Other oral conditions: Wearing dentures, especially upper dentures, or having conditions that cause dry mouth can increase the risk of oral thrush.
Source: Mayo Clinic