It is not recommended to mix breastmilk expressed at different times to prevent the deterioration of one portion of breastmilk from affecting the other portion of normal breastmilk, and to prevent adverse effects on the baby. Normally, it is not recommended to mix breastmilk expressed at different times, mainly because breastmilk expressed too early, if not stored properly, may have already harbored bacteria, and the milk may have deteriorated, and the nutritional value of the breastmilk will be significantly reduced. If you mix it with fresh breastmilk at this time, it will also affect the quality of normal breastmilk and make it spoil. If the baby accidentally eat spoiled breast milk, to a certain extent, it will cause adverse effects on the baby, aggravate the burden on the gastrointestinal tract, easy to abdominal pain, bloating, diarrhea, nausea, vomiting and other symptoms. In daily life, parents need to reasonably preserve breastmilk and try to let the baby drink fresh breastmilk. To summarize, since mixing breastmilk expressed at different times is a safety hazard for babies, it is not recommended. If your baby develops abnormalities after breastfeeding, you need to go to the hospital in time.