To understand constipation, it helps to know how the colon (large intestine) works. As food moves
through it, the colon absorbs water while forming waste products, or stool. Muscle contractions in the
colon push the stool toward the rectum. By the time stool reaches the rectum, it is solid because most of
the water has been absorbed. The hard and dry stools of constipation occur when the colon absorbs too
much water. This happens because the colon's muscle contractions are slow or sluggish, causing the stool
to move through the colon too slowly. Below is a list of the most common causes of constipation.