The main reasons for tooth odor are: 1, tooth decay will lead to tooth odor, because there will be a lot of food residue and disease-causing bacteria in the cavity, and these dirty things will produce odor in the cavity. In addition, it is difficult to remove the food residue in the cavity, which will lead to further infection of the teeth, causing a vicious circle that will make the cavity bigger and bigger, until the inflammation of the dental pulp. 2, periodontitis will cause the teeth to smell bad, periodontitis will cause a lot of tartar, soft tartar and plaque around the teeth and in the periodontal pockets, these substances will breed corruption and produce bad smell on the one hand. On the other hand, it will also stimulate the gums, making the gums red, inflamed and prone to bleeding. 3, wisdom teeth pericoronitis can also lead to tooth odor, wisdom teeth pericoronitis is due to the wisdom teeth above a blind gum pocket, which retains food debris and bacteria. Once inflamed, it can lead to redness and pain in the soft tissues around the pericoronal pocket of the wisdom tooth, and even cause the pocket to overflow with pus.