What causes fecal incontinence?
Fecal incontinence has many causes, including:
Diarrhea can cause fecal incontinence. Loose stools fill the rectum quickly and are more difficult to hold than solid stools. Diarrhea increases the chance of not reaching a bathroom in time.
Constipation can lead to large, hard stools that stretch the rectum and cause the internal sphincter muscles to relax by reflex. Watery stool builds up behind the hard stool and may leak out around the hard stool, leading to fecal incontinence.
The type of constipation that is most likely to lead to fecal incontinence occurs when people are unable to relax their external sphincter and pelvic floor muscles when straining to have a bowel movement, often mistakenly squeezing these muscles instead of relaxing them. This squeezing makes it difficult to pass stool and may lead to a large amount of stool in the rectum. This type of constipation, called dyssynergic defecation or disordered defecation, is a result of faulty learning. For example, children or adults who have pain when having a bowel movement may unconsciously learn to squeeze their muscles to delay the bowel movement and avoid pain.
Injury to one or both of the sphincter muscles can cause fecal incontinence. If these muscles, called the external and internal anal sphincter muscles, are damaged or weakened, they may not be strong enough to keep the anus closed and prevent stool from leaking. Trauma, childbirth injuries, cancer surgery, and hemorrhoid surgery are possible causes of injury to the sphincters.
The anal sphincter muscles won’t open and close properly if the nerves that control them are damaged. Likewise, if the nerves that sense stool in the rectum are damaged, a person may not feel the urge to go to the bathroom. Both types of nerve damage can lead to fecal incontinence. Possible sources of nerve damage are childbirth; a long-term habit of straining to pass stool; spinal cord injury; and diseases, such as diabetes and multiple sclerosis, that affect the nerves that go to the sphincter muscles and rectum. Brain injuries from stroke, head trauma, or certain diseases can also cause fecal incontinence.
Normally, the rectum stretches to hold stool until a person has a bowel movement. Rectal surgery, radiation treatment, and inflammatory bowel diseases can cause the rectal walls to become stiff. The rectum then can’t stretch as much to hold stool, increasing the risk of fecal incontinence.
Childbirth sometimes causes injuries to muscles and nerves in the pelvic floor. The risk is greater if forceps are used to help deliver the baby or if an episiotomy is performed. Fecal incontinence related to childbirth can appear soon after delivery or many years later.
External hemorrhoids, which develop under the skin around the anus, can prevent the anal sphincter muscles from closing completely. Rectal prolapse, a condition that causes the rectum to drop down through the anus, can also prevent the anal sphincter muscles from closing well enough to prevent leakage. Small amounts of mucus or liquid stool can then leak through the anus.
Rectocele is a condition that causes the rectum to protrude through the vagina. Rectocele can happen when the thin layer of muscles separating the rectum from the vagina becomes weak. For women with rectocele, straining to have a bowel movement may be less effective because rectocele reduces the amount of downward force through the anus. The result may be retention of stool in the rectum.
People who are inactive, especially those who spend many hours a day sitting or lying down, have an increased risk of retaining a large amount of stool in the rectum. Liquid stool can then leak around the more solid stool. Frail, older adults are most likely to develop constipation-related fecal incontinence for this reason.
