Hello, Formula milk may cause diarrhea and this is the case if your daughter develops an allergy to certain ingredients in the milk, especially to milk proteins. You may try to use a different milk formula or a Soy-based milk formula. Meanwhile, your child is 8 months old, which means she should be taking other food in increasing amounts and the milk will not be her major food. So, try to give her a healthy diet with fruit and vegetables and the rest of the food as recommended for her age. I hope this answers your query. I remain at your disposal in case further medical assistance is needed. Regards, Dr. Antoneta Zotaj General and Family Physician