Why does tooth decay start when the pH of mouth is lower than 5.5?

Tooth decay starts when the pH of the mouth is lower than 5.5 because the mouth turns acidic when pH is below 5.5 the bacteria produces acids by the breaking down of food particles in our mouth. Enamel is made up of calcium phosphate and it is very hardest part in our body. Tooth decay so can be prevented by taking proper treatment by our self.