Diabetes affects your immune system, leaving you more vulnerable to infection. One common among people with diabetes is a yeast infection called oral thrush (candidiasis). The yeast thrive on the higher amount of sugar found in your saliva, and it looks like a white layer coating your tongue and the insides of your cheeks. Thrush is more common in people who wear dentures and can often leave a bad taste in your mouth. See your dentist if you think you have thrush or any other mouth infection.