The causes of bad breath in 13-year-old children include the following: 1, poor oral hygiene: children’s poor oral hygiene cleaning, a large amount of debris and soft scale accumulate on the tooth surface, and the formation of calculus, stimulating the gums swelling, bleeding, producing a bloody smell. 2, the adjacent surface of the teeth embedded food fibers: under the fermentation of bacteria, emitting odor, and stimulate the inflammation of the gingival papillae, oozing blood. 3, the formation of deeper cavities in the crown of the teeth: this will stagnate 4.Necrotizing gingivostomatitis: When the child’s body resistance is poor and necrotizing gingivostomatitis is triggered, there will be a wide range of soft tissue necrosis and blood oozing in the oral cavity, emitting a strong bad breath. 5.Indigestion: When the child’s gastrointestinal function is weak, resulting in poor food digestion, reflux gastritis can be formed and bad breath can occur.