A stoma is created when a surgeon brings part of the intestine (or, less commonly, the urinary tract) through the abdominal wall so waste can exit the body into an external pouch. The most common reason someone needs a stoma is bowel cancer, but the full list of causes spans serious infections, inflammatory diseases, traumatic injuries, and birth defects. In a large study of over 800,000 colorectal surgeries, about 1 in 6 patients required a stoma.
How a Stoma Is Created
During surgery, the surgeon cuts a small circular opening in the skin, roughly 2.5 centimeters across, at a pre-marked spot on the abdomen. They part the layers of tissue underneath, split the abdominal muscle along its natural grain, and guide the divided end of the bowel through the opening to the surface. The exposed portion of intestine, pink and moist, becomes the stoma itself. A pouching system is then fitted over it to collect waste.
There are three main types. A colostomy brings part of the large intestine to the surface. An ileostomy uses the small intestine instead, typically when the entire colon has been removed. A urostomy reroutes urine through a small piece of intestine to the abdominal wall, bypassing the bladder entirely.
Bowel Cancer
Cancer of the colon or rectum is the single most frequent reason a stoma is formed. When a tumor sits low in the rectum, removing it sometimes means removing the anus as well, which makes a permanent colostomy necessary. In other cases, the surgeon reconnects the bowel after cutting out the cancer but creates a temporary stoma upstream to protect the healing connection. That temporary stoma is typically reversed after several months once the surgical site has healed.
Rectal cancer that cannot be surgically removed may also require a stoma purely for comfort, diverting stool away from a tumor that is blocking the bowel.
Inflammatory Bowel Disease
Crohn’s disease and ulcerative colitis can both damage the bowel severely enough to require a stoma. In ulcerative colitis, the standard surgical treatment removes the entire colon and rectum. Surgeons often construct an internal pouch from the small intestine and connect it to the anus, but a temporary ileostomy protects that pouch while it heals. If the pouch fails, a permanent ileostomy replaces it.
Crohn’s disease presents its own challenges. It can cause deep fistulas (abnormal tunnels between the bowel and skin or other organs), strictures that narrow the intestine, and abscesses that don’t heal. These complications frequently require stoma surgery, and because Crohn’s tends to recur near the stoma site, patients with Crohn’s undergo stoma reconstruction more often than other patients. In one study, 67% of Crohn’s patients who needed repeat surgery had disease that had come back in the small intestine near their stoma.
Diverticulitis
Diverticulitis occurs when small pouches in the colon wall become infected or inflamed. Most cases resolve with antibiotics, but a severe episode can perforate the bowel, spilling its contents into the abdominal cavity. This is a surgical emergency. About 1 in 5 patients hospitalized for diverticular disease need urgent surgical removal of the damaged colon segment, and the surgeon typically creates a colostomy rather than reconnecting the bowel in that infected environment. Among patients who avoid surgery during their first hospitalization, roughly 5.5% still end up needing an emergency colostomy during a later flare.
These stomas are often temporary. Once the infection clears and the remaining bowel heals, a second surgery can reconnect everything. A double-barrel colostomy, where both ends of the divided bowel are brought to the surface, is particularly common in these emergencies because it’s designed for later reversal.
Trauma and Emergency Injuries
Penetrating injuries (stab wounds, gunshot wounds) and blunt force trauma to the abdomen can tear or perforate the intestine, requiring emergency stoma creation. In one study of 74 emergency stoma patients, penetrating injuries accounted for about 23% and blunt abdominal injuries for nearly 14%. Intestinal obstruction, where something physically blocks the bowel, was the most common emergency cause at 44%. Bowel ischemia, where blood supply to a section of intestine is cut off, accounted for another 5%.
Emergency stomas are created quickly under high-stress conditions, so they tend to carry higher complication rates than planned stomas. Many are temporary, reversed once the patient stabilizes and the bowel heals.
Bladder Cancer and Urinary Conditions
When bladder cancer requires removal of the entire bladder, the surgeon creates a urostomy to give urine a new exit route. This is the most common reason for a urinary stoma. In a follow-up study of 66 urostomy patients, two-thirds had undergone the procedure for bladder cancer, while the remaining third had it for severe incontinence or bladder dysfunction, including damage from neurological conditions or prior radiation treatment. Urostomies are almost always permanent.
Birth Defects in Newborns
Some babies are born with conditions that prevent normal bowel function and require a stoma within days of birth.
Anorectal malformations, where the anus or rectum doesn’t form correctly, affect roughly 1 in 1,500 to 1 in 5,000 newborns. Babies with moderate to severe forms often need a diverting colostomy at birth, giving surgeons time to reconstruct the anatomy in later operations.
Hirschsprung’s disease is a rarer condition where nerve cells are missing from a section of the colon, leaving it unable to push stool through. When bowel washouts fail to manage the condition, a stoma is created to bypass the affected segment until corrective surgery can be performed. Both conditions typically lead to temporary stomas that are reversed once the reconstructive surgery is complete and healing is confirmed.
Other Causes
Several less common conditions can also lead to stoma creation. Radiation proctitis, where previous cancer radiation damages the rectum, may require a stoma to divert stool away from the injured tissue. Severe fecal incontinence that hasn’t responded to other treatments can be managed with a permanent colostomy. Familial adenomatous polyposis, a genetic condition that produces hundreds of precancerous polyps in the colon, often requires complete colon removal and a stoma.
Temporary vs. Permanent
Whether a stoma is temporary or permanent depends on how much bowel remains, whether the anus is intact, and whether the underlying disease is likely to recur. A temporary stoma lets a surgical connection or an injured section of bowel rest and heal. After several months, a second surgery reconnects the bowel, and stool passes through the anus again. Loop stomas, where the bowel is brought to the surface in a loop rather than cut completely, are designed with reversal in mind.
A permanent stoma is necessary when the anus or too much of the colon has been removed or damaged beyond repair. Advanced rectal cancer requiring removal of the anus, complete bladder removal for cancer, and failed internal pouches after ulcerative colitis surgery all typically result in permanent stomas. An end colostomy or end ileostomy, where the bowel is divided and only one end is brought to the surface, is the most common permanent configuration.