Tooth decay begins when the pH of the mouth drops below 5.5 because this acidic environment starts to dissolve the minerals in tooth enamel, which is a protective layer on your teeth. Enamel is made primarily of calcium and phosphate, and when the pH is low, these minerals can be lost more easily. If the acidity persists, it can lead to cavities and decay. Maintaining a neutral pH (around 7) helps protect your teeth from this process.
