Problems with the normal functioning of the rectum, anus or central nervous system (CNS) can lead to fecal incontinence. Such difficulties may include:

• Constipation. Difficulty passing hard, dry stool (feces) or the inability to pass stool. This is one of the most common causes of fecal incontinence. Constipation causes large, hard stools to become lodged in the rectum. Watery stool can then leak out around the hardened stool. Constipation also causes the rectal muscles to stretch, which weakens them so they cannot hold stool long enough for a person to reach the toilet.
• Diarrhea. Loose or watery stool. It is more difficult to control loose stool than solid stool, which can result in fecal incontinence. Diarrhea can cause an accident even in people who do not have incontinence.
• Muscle damage. Damage to the anal sphincter muscles can prevent them from tightening enough to keep stool inside the rectum. Muscle damage may be caused by experiences such as vaginal childbirth (especially multiple births) or anal surgery (e.g., hemorrhoid surgery). An episiotomy (incision made to enlarge the vaginal opening) during childbirth may increase the likelihood of sphincter muscle damage that can lead to fecal incontinence. Hysterectomy (surgical removal of the uterus) may also increase the risk of fecal incontinence.
  
  In addition, fecal incontinence is more common among older adults than younger age groups, partially because the elderly experience a general muscle weakening that occurs with age.
• Nerve damage. Problems with nerves that control rectal and anal sphincter activity can result in the inability to sense fullness of the bowel. This may lead to the unexpected release of stool because the sensation that usually precedes and indicates readiness for a bowel movement does not occur. Nerve problems may also prevent sphincter muscles from properly tightening, allowing stool to spill from the rectum.
  
  Nerve damage may be due to a number of conditions or events, which can range from childbirth to stroke. For instance, the use of forceps during delivery may increase the risk of nerve damage that can lead to fecal incontinence. Nerve damage may develop over time due to injury or disease, such as diabetes (the body’s inability to break down blood sugar), multiple sclerosis (an autoimmune disease affecting the central nervous system), and dementia (impairment of brain functioning). Nerves can also become damaged in people with a long-term habit of straining to pass stool.
  
  
• Loss of storage capacity. Normally, the rectum stretches to hold stool. However, scarring of rectal tissue can make the walls of the rectum stiff and less elastic. When the rectum cannot stretch as much, it cannot hold as much stool, causing fecal incontinence. Rectal surgery, radiation treatment and inflammatory bowel disease (IBS) can all cause rectal scarring. IBS also can make rectal walls irritated and unable to contain stool.
• Hemorrhoids. May prevent the anal sphincters from closing and cause fecal incontinence.
• Pelvic floor dysfunction. Problems with the layers of muscles and connective tissue that form the floor of the pelvis and help to maintain continence (the ability to control the timing of a bowel movement or urination). Childbirth is the most common cause of pelvic floor dysfunction in women. Other causes of pelvic floor dysfunction include:
  
  
  • Decreased perception of rectal sensation
    
  • Decreased anal canal pressure
  • Impaired anal sensation
  • Rectal prolapse (a dropping down of the rectum)
  • Rectocele (protrusion of the rectum through the vagina)
  • Generalized weakness and sagging of the pelvic floor

Sometimes the cause of fecal incontinence cannot be determined (idiopathic). This occurs most commonly in middle-aged or older women.