The reasons are as follows: 1. Expired milk is prone to breeding pathogenic microorganisms, if you drink expired milk again will cause pathogenic microorganisms into the body, which may cause abdominal distension, abdominal pain and other infectious diseases. 2. The nutrients in expired milk have been decomposed and consumed, so the consumption of such milk can not play a supplementary nutritional role. 3. The first thing you need to do is to take a look at the product.