Proctitis is most often caused by sexually transmitted infections (STIs) such as
herpes simplex virus that are passed through receptive anal sexual contact. This includes both penetrative sex and sexual activities where there is an exchange of body fluids or skin-to-skin contact. You can also get these infections by sharing sex toys. If you have one of these infections, you can pass it to others even if you don’t have symptoms.
Proctitis may also be a side effect of medical treatments like radiation therapy and medications, or it may be related to conditions that cause inflammation such as ulcerative colitis or Crohn's disease. Other causes include rectal injury, surgery, infections that are not sexually transmitted, and food allergies.