There are many causes of anal stenosis, the first one, congenital anal stenosis, is born with a small anus and is a congenital anorectal development abnormality. The second, acquired anorectal stenosis, is mainly caused by trauma or burns, which sometimes cause scarring and result in anorectal stenosis. The third, anorectal surgery, such as after internal hemorrhoids or mixed hemorrhoids, if the mucosa and skin are damaged too much during the surgery and the sclerosing agent is injected too deeply, this may lead to inflammation around the anorectum, thus forming a scar and causing stenosis. Fourthly, malignant tumor of rectum, the rapid growth of the tumor leads to compression and infiltration, which stenoses the intestinal lumen. So there are many causes of anal stenosis.