The colon is another word for the bottom portion of the large intestine leading to the rectum. By the time food reaches the large intestine, the stomach and small intestines have already digested it. The colon stores waste, absorbs water and helps maintain a healthy electrolyte and water balance.
Proponents of colon cleanses believe that many common ailments---such as acne or constipation---can be traced back to toxins in the colon. They argue that poor diet, poor lifestyle choices and environmental pollutants all lead to toxic buildup in the colon. Because the colon must be functioning properly for the liver to function properly, and because the liver must function properly for the kidneys to function properly, the colon can be implicated in setting off a "chain reaction" that affects the health of the whole body. Cleansing the colon of these toxins reportedly leads to better overall health.