The end of the bearded dragon's tail is usually darker in color. However, if you notice that it has changed from what was before or starts to look like something might be wrong with its condition then there could potentially be some serious problems. If left untreated, tail rot can become a serious, even life-threatening condition, so a trip to the veterinarian is always recommended at the first sign of illness. Tail rot can be caused by an infected cut or a constriction produced by old skin that hasn't been removed correctly.