Does tooth sensitivity to cold mean a cavity? If a tooth is highly sensitive for more than three or four days and reacts to both hot and cold temperatures, it's best to ask your dentist to take a closer look. Sometimes sensitivity may actually be a sign of a cavity or infected tooth pulp. Why is my tooth sensitive all of a sudden? Tooth sensitivity is caused by worn tooth enamel or exposed nerves in your teeth. When you eat or drink something with an extremely low or high temperature, you may feel a sudden, sharp flash of pain.