When foods containing sugars or starches are eaten, the bacteria in the mouth (in plaque) convert these products to acids that can lead to dissolving of the tooth enamel. Over time, this can cause the enamel to break down and a cavity to form, which may require filling by a dentist. While decay is a localized process (ie: it does not affect all of the teeth at one time), erosion occurs across the whole tooth surface that has been exposed to acid. It does not involve bacteria or dietary sugars, but is the result of direct action of acids (either from food, drinks or the stomach) on the tooth enamel surface. Over time, this acidic softening can result in significant wear, leading to reduced thickness of enamel and a change in texture, shape and appearance of teeth, which may also lead to tooth sensitivity.