Anal fissure: This condition is characterized by a tear in the lining of the anus, which can cause severe pain during and after bowel movements. The pain is often described as sharp or burning and can be exacerbated by defecation.

Hemorrhoids: Enlarged veins in the rectum or anus can cause pain, especially if they become thrombosed. The pain can be severe and is often accompanied by swelling and bleeding.
Proctalgia fugax: This condition involves sudden, severe pain in the anus that can last from seconds to minutes. It is often caused by muscle spasms in the anal sphincter.
Levator ani syndrome: This condition involves pain and discomfort in the rectum and anus due to spasms of the levator ani muscle. The pain can be severe and is often chronic.

Rectal cancer: Although less common, rectal cancer can cause severe pain in the anus and distal rectum, especially if the tumor is large or has invaded surrounding tissues.
Abscess (perianal or perirectal): An abscess in the perianal or perirectal region can cause severe, constant pain, and if left untreated, can lead to serious complications such as sepsis.
Fistula-in-ano: An abnormal connection between the inside of the anus and the skin around it can cause pain, especially if it becomes infected.

Coccydynia: Pain in the coccyx (tailbone) can radiate to the anus and distal rectum, causing severe discomfort. This condition is often caused by trauma to the coccyx.
Pudendal neuralgia: This condition involves pain in the distribution of the pudendal nerve, which can include the anus, perineum, and genital area. The pain can be severe and is often described as burning or stabbing.
Solitary rectal ulcer syndrome: This condition involves ulcers in the rectum, which can cause pain, bleeding, and difficulty with bowel movements. It is often associated with chronic constipation and straining during defecation.