The anal sphincter muscles are two muscles at the end of the rectum called the internal and external sphincter muscles. These keep stool inside the rectum. Bowel incontinence may be caused by the following:
- an abscess or inflammation in the rectum or perianal area
- damage to the anal sphincter muscles or pelvic floor muscles from complications or trauma of childbirth
- nerve damage resulting from childbirth neurologic disorders
- complications of a previous operation
- hemorrhoid surgery
- physical disability due to an injury
- diseases that affect the nerves such as diabetes or multiple sclerosis can also cause damage to the nerves that control the anal sphincters or sense stool in the rectum
- chronic constipation or diarrhea
Loss of storage capacity in the rectum, which may also cause fecal incontinence, may result from radiation treatment and rectal surgery. Inflammatory bowel disease (IBD) may cause rectal scarring that stiffens the walls of the rectum, which in turn cannot stretch to hold as much stool.
Pelvic floor dysfunction can also cause fecal dysfunction. This may be seen in rectal prolapse, protrusion of the rectum out of the anus, and rectocele, a protrusion of the rectum through the vagina. Often women do not experience symptoms of fecal incontinence due to pelvic floor dysfunction until their mid-40s or later.