Fecal incontinence (FI), or in some forms encopresis, is a lack of control over defecation, leading to involuntary loss of bowel contents, both liquid stool elements and mucus, or solid feces. When this loss includes flatus (gas), it is referred to as anal incontinence. FI is a sign or a symptom, not a diagnosis. Incontinence can result from different causes and might occur with either constipation or diarrhea. Continence is maintained by several interrelated factors, including the anal sampling mechanism, and incontinence usually results from deficiency of multiple mechanisms. The most common causes are thought to be immediate or delayed damage from childbirth, complications from prior anorectal surgery (especially involving the anal sphincters or hemorrhoidal vascular cushions), altered bowel habits (e.g., caused by irritable bowel syndrome, Crohns disease, ulcerative colitis, food intolerance, or constipation with overflow incontinence), and receptive anal sex. An estimated 2.2% of community dwelling adults are affected. However, reported prevalence figures vary. A prevalence of 8.39% among non-institutionalized U.S adults between 2005 and 2010 has been reported, and among institutionalized elders figures come close to 50%.Fecal incontinence has three main consequences: local reactions of the perianal skin and urinary tract, including maceration (softening and whitening of skin due to continuous moisture), urinary tract infections, or decubitus ulcers (pressure sores); a financial expense for individuals (due to cost of medication and incontinence products, and loss of productivity), employers (days off), and medical insurers and society generally (health care costs, unemployment); and an associated decrease in quality of life.
lower anterior resection, often performed for colorectal cancer), radiotherapy directed at the rectum, and inflammatory bowel disease can cause scarring, which may result in the walls of the rectum becoming stiff and inelastic, reducing compliance. Reduced rectal storage capacity may lead to urge incontinence, where there is an urgent need to defecate as soon as stool enters the rectum, where normally stool would be stored until there was enough to distend the rectal walls and initiate the defecation cycle. Tumors and strictures also may impair reservoir function. Conversely, increased rectal volume (megarectum), may cause fecal loading and overflow FI. Reduced rectal sensation may be a contributory factor. If the sensory nerves are damaged, detection of stool in the rectum is dulled or absent, and the person will not feel the need to defecate until too late. Rectal hyposensitivity may manifest as constipation, FI, or both. Rectal hyposensitivity was reported to be present in 10% of people with FI. Pudendal neuropathy is one cause of rectal hyposensitivity, and may lead to fecal loading/impaction, megarectum and overflow FI. Normal evacuation of rectal contents is 90-100%. If there is incomplete evacuation during defecation, residual stool will be left in the rectum and threaten continence once defecation is finished. This is a feature of people with soiling secondary to obstructed defecation. Obstructed defecation is often due to anismus (paradoxical contraction or relaxation failure of the puborectalis). : 38  Whilst anismus is largely a functional disorder, organic pathologic lesions may mechanically interfere with rectal evacuation.