If breast milk is placed in a 40°C milk warmer, it is not recommended to leave it for more than half an hour, and at most, not more than 2 hours. The temperature of 40℃ is suitable for bacteria growth. If breast milk is left at this temperature for too long, the nutrients in it may change, which will eventually lead to spoilage. If your baby accidentally drinks spoiled breastmilk, diarrhea, gastrointestinal discomfort and crying may occur, which is detrimental to your baby’s growth and may even be dangerous. Therefore, it is recommended that breast milk be kept in a 40 degree milk warmer for no more than half an hour. If your baby is not around, you can store your breast milk in a disposable bag with milk storage and keep it in the refrigerator for a while, usually for no more than 24 hours. However, if conditions allow, it is better to let your baby drink fresh breast milk for the sake of your baby’s health.