Doctors recommend that everyone have an initial colonoscopy at 50—sometimes earlier if you have risk factors, such as Crohn's disease or a family history of colon cancer. People with Crohn's begin colon cancer screening when they've had Crohn's for at least eight years, with follow up colonoscopies every one to two years.

During a colonoscopy, your doctor examines the inside of your colon with a long, flexible tube that has a video camera on the end. He or she can check for cancer and remove any polyps (growths on the intestinal wall) they find. Polyps are generally benign but may turn into cancer so removing them is an important part of colon cancer prevention. In order for your physician to have an unobstructed view of your colon, you must thoroughly clean and empty your bowels before the colonoscopy.

Your physician will provide instructions for cleansing your bowel. Generally, this process takes the full day and evening before your appointment. Most bowel cleaning preparations involve mixing a bowel stimulator with fluids, and sticking to a diet that consists primarily of clear liquids. You will consume quite a lot of fluid, and the cleansing mixture does cause diarrhea. You'll need to spend the day close to a bathroom.

Bowel cleansing products are usually made from phospho-soda, sodium phosphate solutions or tablets, or polyethylene glycol. The Food and Drug Administration has issued warnings about bowel cleansing products made from Oral Sodium Phosphate, which may cause kidney damage. Although rare, the risk is greater in people who have a bowel obstruction or colitis.

The actual colonoscopy procedure is painless and only takes about 20 minutes. Proper preparation, however, is critical. Follow your physician's instructions carefully.