Bad breath in infants may be caused by inadequate oral hygiene, digestive disorders, mouth ulcers and so on. 1. Oral cleaning is not in place: babies do not rinse their mouths with water in a timely manner after breastfeeding, which may produce a milk odor. If the mouth is not cleaned properly after adding complementary foods, the food residues in the mouth produce a bad odor, which can also cause bad breath. 2. Digestive disorders: If the baby is fed too much milk, improper addition of complementary foods can lead to gastrointestinal digestive disorders, food indigestion, resulting in bad breath. 3. Mouth ulcers: infants are prone to mouth ulcers if they lack vitamins or have weak immunity. The epidermal tissue in the mouth of the affected child becomes necrotic and produces a foul odor. There may be other causes of bad breath in infants, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, under the guidance of the doctor to give targeted treatment or treatment.