If you have persistent bad breath or a bad taste in your mouth, it could be a sign of tooth decay. Of course, if you have pain in your tooth when you drink something hot or cold or eat a sugary food, all of these will be caused by tooth decay. If the decay is between two teeth, food particles getting stuck there is also a sign of tooth decay. Decay does not always look pitch black. Sometimes it can look chalky white. In other words, tooth sensitivity, food getting stuck in that area and bad breath are signs of tooth decay.