Diarrhea the day after drinking beer is considered to be caused by the irritating damage to the gastrointestinal mucosa caused by the alcohol in beer or by the presence of pathogenic microorganisms in beer, or by the low temperature of beer. Beer contains a certain amount of alcohol, which is a strong irritant and can disrupt the normal peristaltic function of the intestine after entering the gastrointestinal tract, affecting the normal flora in the intestine and causing diarrhea due to intestinal dysfunction. If beer is not stored properly, excessive sunlight and other phenomena can cause it to deteriorate. The beer will then contain disease-causing microorganisms, and people will also have diarrhea after drinking it. In addition, if you choose to drink beer at a lower temperature, it will also stimulate the gastrointestinal tract and cause intestinal stress, leading to diarrhea. It is advisable to quit drinking alcohol.