Each type of food has different chemical properties and pH levels. Sugars are simple carbohydrates. They’re broken down quickly, starting when they come into contact with saliva. When this process happens, acidic byproducts are created, fueling additional plaque formation. Even artificial sweeteners contribute to this process (“sugar free” doesn’t mean “cavity free”!)
It’s plaque that processes the sugar, creating additional acids inside of the mouth. Higher levels of acids and more frequent exposure — such as eating sugar on a frequent basis — can increase cavity formation.
Sugar is often used as an additive to make foods more palatable, it’s also found naturally in many products such as milk and fruit juice. Eating food with any type of sugar, natural or not, will create an acid byproduct as soon as it’s broken down by saliva.