A large lump outside the anus may be caused by hemorrhoids, rectal polyps, warts and other factors. 1. Hemorrhoids: may be related to bad habits, poor bowel habits, chronic constipation and other factors, can lead to the appearance of pimples on the outside of the anus, usually hard lumps, accompanied by anal moisture, itching and other symptoms. 2. Rectal polyps: when there are rectal polyps, it will also make the outside of the anus appear lumps, usually accompanied by blood in the stool, abdominal pain, diarrhea, pus and blood stools and other symptoms, and in serious cases, there will be cancer. 3. Condyloma acuminatum: may be related to unclean sex, can lead to the anus or genital area of the cauliflower pattern bumps, accompanied by mild itching as well as tingling, with a certain degree of contagious. If you have a big pimple on the outside of your anus and there are other abnormalities, it is recommended that you go to the hospital in time to have a checkup, clarify the cause of the disease, and give reasonable treatment to avoid delaying your condition.