White or brown stains on the tooth A visible hole in your tooth What happens if you don't treat a cavity? A cavity will not go away on its own. If you leave a cavity untreated, it only continues to grow and cause further decay to your tooth. Advertisement Here's how a cavity can progress if you don't treat it: 1. As a cavity forms, your enamel starts to weaken as a result of plaque buildup on your tooth. Enamel is the hard protective outer layer of your tooth. You can still avoid a cavity with flouride treatments done by your dentist.