Newborns farting hard and painfully may be caused by indigestion, lactose intolerance and so on. 1. Indigestion: Newborns grow fast and have a high demand for nutrients, but their digestive system is not perfect, so if they are not fed properly, they may suffer from indigestion, which can lead to constipation and painful farting. 2. Lactose intolerance: Breast milk and milk powder both contain a certain amount of lactose, and breast milk has a higher lactose content. When newborns are lactose intolerant, they are prone to farting hard and painfully, which can be accompanied by milk overflow, bloating, abdominal pain, diarrhea, and sour stools. There are other reasons why newborns fart hard and painfully, so it is recommended that you seek medical attention for a clear examination and targeted treatment.