What causes cavities? Fermentable carbohydrates—mainly man-made sugars. The cavity-causing bacteria is called Strep Mutans. It lives and thrives in an acidic environment. No sugar + No Strep Mutans= No Tooth Decay! The acids that cause cavities are a byproduct of Strep Mutans fermentation. To reduce decay – reduce the sugar intake. With each exposure, there is a ~20 minute production of acid in the saliva. Therefore, if one ingests sugar all day long, acid will continue to demineralize the teeth, and decay will ensue. Select good snacks to reduce the acidic effect, such fresh veggies, hummus, nuts, cheese and fruit. Good sugars like fruit have fast oral clearance from the mouth. Sticky sugars cling to the teethand have long lasting effects causing cavities.