Under normal circumstances babies do not have bad breath. Although bad breath is not a simple disease, but may be a warning sign of one or more diseases, such as mouth ulcers, constipation, diarrhea, so it is important to pay attention. There are several reasons for bad breath in babies: one is indigestion in babies, resulting in “gastric reflux”, which releases the foul smell of food mixed in the stomach. The second is improper cleaning of the mouth, bacteria breeding, producing volatile odor. Third, the abuse of antibiotics, so that the gastrointestinal tract flora imbalance, normal bacteria, such as lactobacilli are inhibited, but the growth of miscellaneous bacteria multiply. There are also diseases that can cause bad breath. Hepatitis or other causes of liver impairment can cause a child to exhale a smell similar to rotten eggs, indicating severe impairment of liver function. Children with diabetes who reach the stage of ketoacidosis will exhale a rotten apple odor. Some children with sinusitis, purulent tonsillitis and other diseases form ulcers at the lesion, erosion, and pus will also have a purulent bad breath smell. This requires parents to pay more attention to observe, long time bad breath to take the child to the hospital in time to check, so as not to delay the child’s condition.