What is the first sign of a cavity? As the decay gets larger, it may cause signs and symptoms such as: Toothache, spontaneous pain or pain that occurs without any apparent cause. Tooth sensitivity. Mild to sharp pain when eating or drinking something sweet, hot or cold How bad is a cavity if it hurts? The acids in plaque damage the enamel covering your teeth. It also creates holes in the tooth called cavities. Cavities usually do not hurt, unless they grow very large and affect nerves or cause a tooth fracture. An untreated cavity can lead to an infection in the tooth called a tooth abscess.