A one-week-old baby with a bad taste in his mouth may be due to indigestion, mouth ulcers, and diet. 1. indigestion: if the baby has indigestion, the gastrointestinal digestive function is reduced, so that the stomach retains the residual food, which will be manifested in the mouth odor and other situations. 2. Mouth ulcers: If the baby has single or multiple ulcers in the mouth due to vitamin deficiency, the surface of the ulcers will be covered with residual food, and the border mucosa will be red and slightly swollen, accompanied by a bad taste in the mouth and ulcer pain and other symptoms. 3. Diet: If the baby recently ate food containing a lot of onions, ginger, garlic, leeks or seafood, lamb and other smell more stimulating food, can also occur in the mouth odor. If the baby’s mouth odor has not been improved for a long time, please consult a doctor to exclude other disease factors.