It is important to rule out any deeper or more severe problems which could cause your teeth to be sensitive. For that, you need to see your dentist. The problem could be as a result of gum problems, or cavities, or cracks in your teeth. Some people, however, just happen to have sensitive teeth. The most likely complaint is sensitivity around the gum line, where gums may have receded due to previous gum problems or overzealous brushing.