Some causes of uncontrollable bowel movements are diarrhea, constipation, surgery and a lessened rectum storage capacity, explains Mayo Clinic. Other potential causes are nerve damage, muscle damage, rectal prolapse or a rectocele, a condition in which a woman's rectum protrudes through her vagina.
Diarrhea can cause worsened bowel incontinence because it is more difficult to retain loosened stools in the rectum, notes Mayo Clinic. Meanwhile, people with chronic constipation may develop bowel incontinence because impacted stools that are too large to pass through the rectum can cause rectum and intestinal muscles to stretch and grow weaker over time. These compromised muscles enable watery stool to make its way around the mass of impacted stool, then leak out of the rectum. Constant straining from constipation can also result in nerve damage that contributes to difficulty controlling bowel movements.
Other potential causes of nerve damage that result in fecal incontinence are stroke, childbirth, diabetes, spinal cord injuries and multiple sclerosis, according to Mayo Clinic. The affected nerves may be either the nerves controlling the anal sphincter or those responsible for sensing fecal matter in the rectum. Childbirth can also result in injury to the muscle rings of the anal sphincter, which is another potential reason for uncontrollable bowels. This type of muscle damage occurs especially in women who undergo episiotomy procedures or have deliveries involving the use of forceps.