The causes of bad breath in 2-year-old babies include systemic factors and local factors in the mouth. The common cause of bad breath in 2-year-old babies is caused by poor oral hygiene. After the baby eats, the food residue or plaque accumulates around the teeth because the baby does not brush well, and the bacteria ferment and produce acid to produce bad breath. It may also be caused by the cavity of tooth decay and the bad breath caused by the food embedment. Or the tooth decay is deeper and reaches the tooth nerve causing pulp tissue septic necrosis and the unique malodor of dead pulp teeth. Bad breath of 2-year-old baby may also be caused by the imperfect digestive function of gastrointestinal tract, because the baby’s digestive system is not well developed, food is not completely digested and decomposed, and bad breath appears, such as eating meat and other indigestible food, or milk, beans and other foods that produce more gas. Or the weather becomes cold, or low resistance is also easy to cause indigestion bad breath. Bad breath in 2-year-old babies may also be a respiratory disease, pneumonia or bronchitis and tonsillitis can also cause bad breath. Misuse of antibiotics leads to dysbiosis of the gastrointestinal flora, lactobacilli are inhibited and the growth of miscellaneous bacteria leads to bad breath. So the causes of bad breath in 2-year-old babies include poor oral hygiene, gastrointestinal indigestion and respiratory diseases.