There are many reasons for sudden bleeding from the anus: 1, there may be bleeding hemorrhoids, hemorrhoids is the varicose veins blood vessels in the abdominal pressure increases or constipation, easy to cause hemorrhoidal veins tortuous, swelling, resulting in hemorrhoidal vein rupture and cause bleeding, in a large amount of alcohol or diet a large number of stimulating food, may appear hemorrhoidal veins tortuous, so, sudden bleeding from the anus is likely to be hemorrhoids. 2, sudden bleeding is likely to be an anal fissure For example, if dry stool stimulates the anal canal, it is easy to lead to anal canal fissure, thus forming anal fissure, which is easy to lead to fresh blood at the fissure when defecation is hard.3, the cause of sudden bleeding from the anus may be rectal polyps and rectal adenomas. If the stool is dry, it is easy to lead to the rupture of the blood vessels under the mucosa of the rectum, which leads to bleeding. Therefore, if the anus suddenly bleeds, you should go to the hospital in time, you should perform rectal diagnosis, and if necessary, perform anoscopy and proctoscopy to clarify the cause and location of bleeding.