Swollen surface next to the anus is hard and painful to touch, which may be caused by thrombosed external hemorrhoids, perianal abscess, anal cancer and other reasons. 1. Thrombosed external hemorrhoid: due to the formation of thrombus at the rupture of blood vessels in the submucosal part of the anal skin, it can be manifested as a hard bag at the anus with pain. 2. Perianal abscess: due to the formation of abscess after the infection of the glands in the anal canal is blocked, it may appear that the surface of the skin next to the anus is swollen and it is hard and painful to touch. 3. Anal cancer: the main symptom is a lump in the anus, accompanied by anal discomfort or itching, with the development of the disease, blood in the stool, pain and other symptoms can occur. It is suggested that people with swollen surface next to the anus, which is hard and painful to touch, should go to the hospital in time to clarify the cause of the disease, and carry out standardized treatment under the guidance of professional doctors as early as possible, so as to avoid delaying the aggravation of the condition.