A tooth that hurts when you touch it may be caused by tooth fracture, caries, periodontitis, pulpitis, apical periodontitis and other causes. 1. Fractured tooth: If the tooth bites hard food or suffers trauma, it may lead to crown fracture or crown-root fracture, root fracture, and the phenomenon of pain when touching a single tooth may occur. 2. Dental caries: when the patient suffers from dental caries, the tooth may have a large cavity, and when food debris enters into the cavity, the phenomenon of pain when a single tooth is touched may occur. 3. Periodontitis: when the patient suffers from periodontitis, most of the tooth roots will be exposed in the oral cavity, at this time the teeth already have different degrees of looseness, there is no way to withstand the pressure of the bite. There will be a single tooth that hurts when you touch it. 4. Pulpitis, apical periodontitis: Bacteria or viruses cause pulpitis by corroding the dentin and invading into the pulp cavity, and the nerve in the pulp cavity is damaged, and if the pulpitis is not dealt with in time, it will develop into apical periodontitis, which will lead to the pain when a single tooth is touched. When a patient has a tooth that hurts when touched, he should go to a regular hospital in time and be treated under the guidance of a professional doctor. So as not to delay the condition and cause adverse consequences.