Frequent diarrhea or constipation. These conditions cause the muscles in the rectum and anus to weaken. When these muscles weaken, the ability to hold stool within the body also weakens.
Muscle damage. Muscle damage can occur during a difficult vaginal childbirth, when doctors have to use forceps or make a small cut (an episiotomy) to make a larger opening. Muscle damage can also result from anal or rectal surgery.
Older age. Muscles in the rectum and anus naturally weaken with age. Other nearby structures in the pelvis area also loosen with age. This adds to the general weakness seen in that area of the body, leading to problems with stool control. Loose stool is more difficult to control than solid stool. When a large amount of loose stool arrives rapidly in the rectum, there may not be enough warning to reach the bathroom in time.
Damage to nerves. If the nerves that control the ability of the rectum and anus muscles to contract are damaged, incontinence can result. Nerves that control "rectal sensation" can also lead to incontinence if they are damaged. Nerve damage can happen during a difficult vaginal delivery, anal surgery, constipation (resulting in bouts of frequent and severe straining), or the presence of certain health conditions (such as diabetes, multiple sclerosis, stroke or a spinal tumor).
Inability of the rectum to stretch. If the muscles of the rectum are not as elastic as they should be, excess stool that builds up can leak out. Inflammatory bowel disease (such as Crohn's disease) can also affect the rectum's ability to stretch. The scars resulting from surgery and radiation therapy can also stiffen the muscles of the rectum.
Other medical conditions. Certain medical conditions, such as rectal prolapse (the rectum falls down into the anus) or rectocele (the rectum pushes into the vagina), or chronic constipation where stool leaks around a large stool ball, can lead to fecal incontinence.
Other causes: Laxative abuse, radiation treatments, certain nervous system and congenital (inherited) defects, inflammation (swelling), and inflammatory bowel disease may affect the ability to control stool.