Colitis, also known as nonspecific ulcerative colitis, is characterized by diarrhea, abdominal pain, mucous stool and purulent bloody stool, acute diarrhea, severe constipation, and inability to pass stool for several days. Sometimes diarrhea and constipation, often accompanied by emaciation and fatigue, and more recurrent attacks.

Colorectal cancer grows slowly, and it takes a long time to grow enough to cause symptoms. Symptoms depend on the type, location and spread of cancer. The intestinal lumen of the right colon is larger in diameter and thinner in wall. Because the intestinal contents are liquid, the symptoms of intestinal obstruction will not appear until the late stage of cancer. The cancer of the ascending colon can grow so big that doctors can touch the tumor mass on the patient's abdominal wall. Fatigue and weakness caused by severe anemia may be the only symptom of patients. The intestinal cavity of the left colon is small and the wall is thick, and the feces are semi-solid. Cancer often grows in a ring shape in this colon, causing constipation and diarrhea to appear alternately. Because the descending colon is narrow and thick, cancer may cause intestinal obstruction earlier. Patients can see a doctor because of abdominal discomfort or abdominal pain and constipation. Patients may have blood in feces or blood mixed in feces, but it is often invisible to the naked eye and needs laboratory examination to find it.

Most cancers are slow bleeding. The most common first symptom of rectal cancer is bleeding during defecation. Regardless of rectal bleeding at any time, doctors should consider the possibility of cancer even if they know that the patient has hemorrhoids or diverticulum. Patients with rectal cancer may feel abdominal pain and endless defecation. Sitting can relieve symptoms, but rectal cancer itself generally does not cause pain unless it spreads to tissues outside the rectum.