There are many causes of fecal incontinence. It occurs when something is wrong within the complex mechanisms of the body that maintain continence. Continence depends on functioning muscles and nerves in and around the rectum and anal canal.

Fecal or bowel incontinence can result from a variety of causes:

Diarrhea, or loose stool, may be associated with a feeling of urgency or stool leakage due to the frequent liquid stools passing through the anal opening. Diarrhea is more difficult to control than solid stool that is formed. Even people who do not have fecal incontinence can have an accident when they have diarrhea.

The pelvic floor plays an important role in maintaining continence and abnormalities of the pelvic floor can lead to fecal incontinence. Examples of some abnormalities are decreased perception of rectal sensation, decreased anal canal pressures, decreased squeeze pressure of the anal canal, impaired anal sensation, a dropping down of the rectum (rectal prolapse), protrusion of the rectum through the vagina (rectocele), and/or generalized weakness and sagging of the pelvic floor. Often the cause of pelvic floor dysfunction is childbirth, and incontinence does not show up until the midforties or later.

Fecal incontinence is most often caused by injury to one or both of the ring-like muscles at the end of the rectum called the anal internal and/or external sphincters. The sphincters keep stool inside. When damaged, the muscles are not strong enough to do their job, and stool can leak out. In women, the damage often happens when giving birth. Anal operations or injury to the tissue surrounding the anal region can damage the anal muscles and hinder bowel control. Infections around the anal area may destroy muscle tissue leading to problems of fecal incontinence.

Fecal incontinence can also be caused by damage to the nerves that control the anal sphincters or to the nerves that sense stool in the rectum. If the nerves that control the sphincters are injured, the muscle does not work properly and incontinence can occur. If the sensory nerves are damaged, they do not sense that stool is in the rectum. You then will not feel the need to use the bathroom until stool has leaked out. Nerve damage can be caused by childbirth, a long-term habit of straining to pass stool, stroke, and diseases that affect the nerves, such as diabetes and multiple sclerosis.

Normally, the rectum stretches to hold stool until you can get to a bathroom. But rectal surgery, radiation treatment, and inflammatory bowel disease can cause scarring that makes the walls of the rectum stiff and less elastic. The rectum then cannot stretch as much and cannot hold stool, and fecal incontinence results. Inflammatory bowel disease also can make rectal walls very irritated and thereby unable to contain stool.

Constipation is one of the most common causes of fecal incontinence and can lead to a large amount of stool in the rectum, a condition called fecal impaction. A fecal impaction is a large mass of dry, hard stool that interferes with normal ability to control bowel movements. A watery stool from higher in the bowel may eventually move around the impaction and leak out.

Other possible causes of fecal incontinence:

- Extended period without defecation
- Severe muscular strain in the abdominal area, particularly when giving birth
- Spinal Cord Injury