Why does tooth decay hurt?

Dental caries is a nerve reaction caused by bacterial infection, so tooth decay shows pain. Dental caries is a clinical manifestation of caries. In the early stages of caries, the outermost layer of teeth is enamel, which has no sensory function, so tooth decay does not feel pain. If the caries is not terminated in time, it will further develop to the dentin layer or dental pulp tissue. The dentin layer has many dentin tubules leading to the dental nerve. The dental pulp tissue has many dental pulp cells with sensory functions. Therefore, the caries is deeper. When it reaches the dentin layer or dental nerve, it will show pain.