Bowel infections are a potential colonoscopy risk, although rare. The colon is not a sterile environment; many bacteria that normally live in the colon ensure the well-functioning of the bowel, and the risk of infections is minimal. Infections can occur during biopsies when too much tissue is removed and bacteria protrude in areas they do not belong to, or in cases when the lining of the colon is perforated and the bacteria get into the abdominal cavity. Infection may also be transmitted between patients if the colonoscope is not cleaned and sterilized properly between tests.