Fecal incontinence has many causes, including
                
- diarrhea  - constipation  - muscle damage or weakness  - nerve damage  - loss of stretch in the rectum  - childbirth by vaginal delivery  - hemorrhoids and rectal prolapse  - rectocele  - inactivity
                
Diarrhea
                
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
                
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.
                
Muscle Damage or Weakness
                
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. Hemorrhoids are swollen blood vessels in and around the anus and lower rectum.
                
Nerve Damage
                
The anal sphincter muscles wont 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.
                
Loss of Stretch in the Rectum
                
Normally, the rectum stretches to hold stool until a person has a bowel movement. Rectal surgery, radiation treatment, and inflammatory bowel diseaseschronic disorders that cause irritation and sores on the lining of the digestive systemcan cause the rectal walls to become stiff. The rectum then cant stretch as much to hold stool, increasing the risk of fecal incontinence.
                
Childbirth by Vaginal Delivery
                
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 episiotomya cut in the vaginal area to prevent the babys head from tearing the vagina during birthis performed. Fecal incontinence related to childbirth can appear soon after delivery or many years later.
                
Hemorrhoids and Rectal Prolapse
                
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
                
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. More research is needed to be sure rectocele increases the risk of fecal incontinence.
                
Inactivity
                
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.