What causes cavities on teeth?

Bacteria: Bacteria in your mouth consume sugars, form acids which then eat into the surface of the tooth. Sugar is not just candy, milk, fruit juice etc. Your real question is how can i stop cavities and the answer is keep them clean, keep the bacteria that can cause acids off and try to maintain a good diet and quit snacks and beverages between meals. Floss is the only way you can clean between the tee.

Acid: Failure to brush and floss properly and daily allows plaque buildup. Plaque combined with fermentable carbohydrates results in an acid by-product that dissolves the teeth causing cavities. Having an acid mouth contributes. All carbonated beverages contain carbonic acid. Some in addition contain citric acid or phosphoric acid. Thus sipping on these drinks contribute to cavities.

Acid and Exposure : As previously explained the acid byproduct of bacterial metabolism etches the enamel and causes "cavities" commonly referred to as decay. Another component however is the frequency of exposure. If you constantly snack on sugary treats the frequency of acid exposure increases the problem. Each exposure results in approximately 20 minutes of acid exposure. I suggest limiting your exposures.

Bacteria : A cavity is a hole left from a bacterial infection that has eroded the tooth. Smoking, sugar, genetics, general and oral health all play a role in one's succeptability to tooth decay.

Many reasons: Bacteria, sugar , decalcification are few reasons check with your dentist.