The sudden onset of pain in the anus can be roughly divided into the following causes: 1, due to inflammation of the rectum, when the inflammation of the rectum is more serious, it can lead to mucosal lesions, the mucosa has a similar ischemic situation, the patient’s pain will suddenly occur. 2, benign lesions caused by bleeding, bleeding after the rectal mucosa may be stimulated, the tension increases will make the patient feel the pain inside the anus. 3, due to perianal abscess, the clinical reaction, in fact, the local skin is thick, abscess can not be discharged out of the body. The clinical reaction caused by perianal abscess, which is actually caused by the thicker local skin and the inability of the abscess to drain out of the body. In clinical terms, it is mainly painful and may be accompanied by general fever. 4. malignant rectal tumor, if the tumor invades the surrounding tissues causing pain, making it unbearable for the patient. Sudden pain in this area, patients should still go to the hospital as soon as possible.