Constipation is one of the most common causes of accidental bowel leakage. 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 muscles of the rectum to stretch, which weakens the muscles so they can’t hold stool in the rectum long enough for a person to reach a bathroom. This may also be associated with a rectocele (rectum bulging into the vagina) especially in women. Also, straining at a bowel movement could predispose to not only sphincter weakness but also vaginal prolapse (bulge) or even rectal bulging out of the opening.
Accidental bowel leakage can be caused by injury to the internal and external sphincters muscles. The sphincters keep the stools inside. When damaged, the muscles aren’t strong enough to do their job and stool can leak out. In women, the damage often happens when giving birth. The risk of injury is greatest if the doctor uses forceps to help deliver the baby or performs an episiotomy, which is a cut in the vaginal area to prevent it from tearing during birth. Hemorrhoid surgery can also damage the sphincters.
Fecal incontinence can be caused by damage to the nerves that control the anal sphincters or the nerves that sense stool in the rectum. If the nerves that control the sphincters are injured, the muscles don’t work properly and incontinence can occur. If the sensory nerves are damaged, they don’t sense that stool is in the rectum so you won’t 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, physical disability due to injury, and diseases that affect the nerves such as diabetes and multiple sclerosis.
Loss of Storage Capacity
Normally, the rectum distends 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 fecal incontinence results. Inflammatory bowel disease also can irritate the rectal walls, making them unable to contain stool.