How do people develop oral yeast infections?

Multple causes: A common oral yeast infection is caused by candida albicans. This is an oppourtunistic fungal infection that is commonly referred to as "thrush". Candida is normally present in the mouth but may proliferate into an "infection" or overgrowth causing symptoms in the mouth. Overgrowth can be caused by immunosuppression, prolonged denture use, stress, or even side effects of medications. Best of luck!

Many ways....: Medications that upset the balance of microorganisms in the mouth and may cause thrush especially corticosteroids and antibiotics, certain medical situations such as uncontrolled diabetes, HIV infection, cancer, hormonal changes, pregnancy, and a dry mouth increase the probability, and even smokers are at a higher risk of developing oral thrush (candidiasis).