9 months old baby bad breath, usually seen in the following cases: First, not good oral hygiene, easy to make the mouth breeding bacteria and other causes of bad breath, usually should give the child a daily cleaning of the mouth. Second, gastroesophageal reflux children, stomach gas is relatively heavy, but also prone to frequent bad breath, this situation is mainly to pay attention to the way of feeding. Third, cold and cold gastroenteritis can appear bad breath, usually seen in the intestinal tract viral infection or bacterial infection, causing digestion and absorption function to reduce the appearance of bad breath. Fourth, there are some babies with poor nutritional status, weak spleen and stomach function of the child, the gastrointestinal tract gas accumulation increases cause bad breath. Fifth, the 9-month-old baby intestinal micro-ecosystem is not well established, in the role of various external factors, prone to dysbiosis caused by indigestion, gas accumulation increased halitosis.