Blood coming out of the anus, blood in the stool, or all blood in the stool, bright red, dark red or tarry in color, are all called blood in the stool. Blood in the stool is only one symptom, and many diseases can cause blood in the stool. Bleeding from the skin or other organs is usually associated with hematologic and other systemic diseases. Blood in the stool alone is usually seen in the lower gastrointestinal tract, especially in the colon and rectum, but occasionally in the upper gastrointestinal tract. Patients usually panic when they see blood in the stool, suspecting that they have cancer and worrying. In fact, clinically different diseases have their own characteristics of blood in the stool: 1, hemorrhoids: blood in the stool usually occurs during or after defecation or before the stool, in the form of drops or jets, blood is bright red, blood and stool do not mix; 2, anal fissure: anal fissure caused by blood in the stool, blood is bright red, dripping or hand paper wipe after the blood, and after the stool there is severe anal pain; 3, rectal, colon polyps: blood is bright red, slightly painful, blood and stool do not 4, ulcerative colitis: bleeding mixed with mucus or pus-blood stool, accompanied by abdominal pain, fever, frequent stools, etc.; 5, colorectal cancer: bright red or dark red blood, mixed with stool, or pus-blood stool accompanied by anorectal drop, wasting, change in bowel habits, change in stool properties and other symptoms. The characteristics of blood in the stool of different groups of people: Children with blood in the stool, mostly caused by rectal polyps, bright red, painless, blood and stool do not mix. In adults, blood in the stool is mostly caused by hemorrhoids, anal fistula, anal fissure, rectal polyps, colon polyps, rectal cancer, colon cancer, bacterial dysentery, etc. Most of them belong to the category of anorectal diseases, which should be noted. 1, young people: the proportion of patients with blood in the stool aged less than 30 years old has risen from 8% to 15% 10 years ago. Generally caused by benign anorectal diseases. 2, the middle-aged and elderly group: with the growth of age, the human sigmoid colon and rectal lesions (including benign and malignant) significantly increased. Patients above middle age, with changes in stool habits, diarrhea or constipation, thinning of stool, stool with mucus and pus and blood should be suspected of the possibility of colorectal cancer, and a few patients may only show fixed abdominal pain.