1. Causes of Diarrhea with Milk Powder Diarrhea is one of the most common digestive problems for babies, and milk powder is the baby’s main source of nutrition. If your baby consumes milk powder that is not suitable for him, it may cause digestive problems such as diarrhea. So what are the causes of diarrhea caused by milk powder? 1.1 Expired milk powder Expired milk powder will produce bacteria and toxins, which can easily cause digestive discomfort. 1.2 The milk powder formula is inappropriate. Every baby’s physical condition is different, and you need to choose milk powder that suits your physical condition.