The most common cause of narrowing of the anus and thinning of the stool is rectal tumors, especially malignant tumors, or rectal cancer, which can cause anal pain and blood in the bowel. The most common is caused by malignant rectal polyps or malignant rectal ulcers. Patients with early diagnosis should be treated promptly with radical resection surgery. In addition, for patients with hemorrhoids, especially severe internal hemorrhoids, stage III and IV internal hemorrhoids, they also tend to lead to narrowing of the anal opening, resulting in thinning of the bowel movements and blood in the bowel movements, and repeated episodes also tend to induce the appearance of anemia. You should actively choose surgical treatment, you can apply the anastomosis to remove the ring of hemorrhoid mucosa, relatively small trauma, post-operative recovery is also faster, usually also pay attention to the hygiene around the anus, treatment of constipation.