The constant pain inside the anus 5 months after internal hemorrhoid surgery may be due to anal stenosis, sinusitis or anal neurosis. 1. Anal stenosis: after internal hemorrhoid surgery, the surgical wound may develop scar contracture, which leads to the appearance of anal stenosis. This disease will cause the patient to have difficulty in defecation, recurrent anal canal mucous membrane rupture or anal fissure causing pain. 2. Sinusitis: Sinusitis is usually caused by bacterial infection. It will cause patients to have anal itching, pain, and anal canal with a feeling of falling, defecation and other symptoms, some patients will have discomfort in the anus after defecation. 3. Anal neurosis: When internal hemorrhoid surgery is performed, improper operation may cause anal neurosis to occur. This disease will cause persistent pain or paroxysmal pain in the anus, anal odor, burning sensation in the anus and other symptoms. Discomfort in the anus after internal hemorrhoid surgery may also be due to recurrence of hemorrhoids.