Left colitis can cause symptoms such as left abdominal pain, bloating, diarrhea and abnormal bowel movements. The colon mainly includes the ascending colon, transverse colon and descending colon, and the colon on the left side of the body is part of the descending colon, where most of the food residues are already formed by the time they are transported to this part and are stored in the sigmoid colon waiting to be expelled. When inflammation occurs in the left side of the colon, inflammatory factors are severely released, causing irritation to the smooth muscle of the intestinal wall and therefore associated with pain in the left side of the abdomen. The inflammatory irritation affects the absorption function of the colon, resulting in a feeling of abdominal distension as the gas in the intestine is not fully absorbed by the body. When inflammation occurs in the intestine, the absorption of water in the intestinal wall is also affected, and the amount of water in the stool will be relatively high, and patients will have more frequent bowel movements and loose stools.