Passing gas during urination, known medically as pneumaturia, almost always signals that air or gas has found its way into the urinary tract from somewhere it does not belong. The most common explanation is an abnormal tunnel, called a fistula, connecting the bowel to the bladder. Less often, a gas-producing bacterial infection inside the bladder itself is responsible. While it can feel bizarre and alarming, pneumaturia is a symptom worth taking seriously because the underlying cause usually needs medical treatment.
How Air Gets Into the Bladder
Your bladder is not supposed to contain gas. When it does, the air has to come from one of a few sources. The most frequent route is a fistula, an abnormal passage that forms between the intestines and the bladder. Because the colon sits right next to the bladder inside the pelvis, conditions that damage the colon wall can erode through to the bladder, creating a direct connection. Once that tunnel exists, bowel gas (and sometimes fecal material) can pass into the bladder and get expelled when you urinate.
A second route is gas produced inside the urinary tract itself. Certain bacteria ferment the sugar in urine, generating carbon dioxide and other gases. This is most likely to happen in people with diabetes, whose urine sugar levels tend to be higher. A third and much less common route is after a medical procedure. Catheterization, cystoscopy, or recent surgery in the pelvic area can introduce a small amount of air, though this typically resolves on its own within a day or two.
Diverticular Disease and Colovesical Fistulas
Diverticular disease is the single most common cause of a bowel-to-bladder fistula, accounting for up to about 80% of all such cases.1PubMed Central. When the bowel meets the bladder: Optimal management of colorectal pathology with urological involvement Diverticula are small pouches that bulge outward through weak spots in the colon wall. They are extremely common in adults over 50 and usually cause no trouble. Problems start when one of those pouches becomes inflamed or infected, a condition called diverticulitis. If the inflammation worsens, the wall of the diverticulum can perforate. That perforation can range from a tiny microabscess to a larger hole. When the perforation erodes toward the bladder, a fistula forms.2Journal of Clinical Gastroenterology. The Natural History of Diverticulitis
The resulting colovesical fistula lets gas and stool-contaminated fluid leak into the bladder. Pneumaturia is the single most reported symptom, occurring in up to 70% of people with this type of fistula.3PubMed Central. Pneumaturia and faecaluria: Symptoms leading to a life-saving diagnosis Some people also notice particles or cloudiness in their urine, which can indicate fecal matter crossing into the bladder. Because fecal bacteria have a direct highway into the urinary system, recurrent urinary tract infections are common in these patients, and those infections are often what finally brings them to a doctor.
Crohn’s Disease and Other Bowel Conditions
Crohn’s disease is another important cause, though it creates fistulas through a different mechanism. Crohn’s produces chronic, deep inflammation that can bore through the full thickness of the intestinal wall. Internal fistulas develop in roughly 5 to 10% of Crohn’s patients. When the fistula runs between the ileum (the last segment of the small intestine) and the bladder dome, it is called an enterovesical fistula, and it produces the same symptoms as a colovesical fistula: air in the urine, recurrent infections, and sometimes visible fecal contamination.4PubMed Central. Entero-vesical fistulas in CROHN’S disease: A case series report and review of the literature
Colorectal cancer is the second most common cause of colovesical fistulas overall, responsible for up to about 20% of cases.1PubMed Central. When the bowel meets the bladder: Optimal management of colorectal pathology with urological involvement A growing tumor in the sigmoid colon or rectum can invade through to the bladder wall. In at least one reported case series, a patient’s initial complaint of fecal-smelling urine lasting about a month turned out to be a colon cancer that had fistulized to the bladder.5PubMed Central. Colon cancer with colovesical fistula: A report of four cases and a literature review This is one reason why pneumaturia should not be brushed off, particularly in older adults. It can be the presenting symptom that leads to an early cancer diagnosis.
Gas-Forming Infections in the Bladder
When no fistula is present, the next possibility doctors consider is emphysematous cystitis, a bladder infection caused by bacteria (or occasionally fungi) that produce gas as a metabolic byproduct. The hallmark of emphysematous cystitis is air collecting inside the bladder wall and lumen without any connection to the intestines.6PubMed Central. Emphysematous Cystitis The usual culprits are common bacteria like E. coli and Klebsiella pneumoniae, which thrive on glucose and produce carbon dioxide gas in the process.
This condition overwhelmingly affects people with diabetes, and for good reason: elevated blood sugar means more glucose spills into the urine, giving gas-forming bacteria a rich fuel source. Emphysematous cystitis is relatively rare in the general population, but it can be life-threatening if the infection spreads or the bladder wall becomes severely compromised. A CT scan typically reveals pockets of gas within or around the bladder wall, which clinches the diagnosis when trauma and fistula have been ruled out.7PubMed Central. Emphysematous Cystitis: A Rare Disease of Genito-Urinary System
In severe cases, the gas-forming infection can travel upward from the bladder to the kidneys, a condition called emphysematous pyelonephritis. One documented case showed extensive gas collections surrounding both kidneys, with air tracking down both ureters.8Kidney International. Bilateral emphysematous pyelonephritis Emphysematous pyelonephritis carries a high mortality rate and often requires aggressive treatment including intravenous antibiotics, drainage, or even surgical removal of the affected kidney. This is the extreme end of the spectrum and underscores why gas in the urine, especially in someone with diabetes, warrants prompt medical attention.
Post-Surgical and Iatrogenic Causes
Pneumaturia can also follow pelvic surgery or procedures involving the urinary tract. A catheter insertion or cystoscopy can introduce a small bubble of room air into the bladder, which usually passes harmlessly within a urination or two. More concerning is when surgery in the pelvis creates an unintended fistula. Radical prostatectomy, for example, occasionally results in a rectovesical fistula, an abnormal connection between the rectum and the bladder. Patients with this complication may experience fecal-smelling urine, gas passage during urination, or even urine leaking from the rectum.9PubMed Central. Repair of a rectovesical fistula following laparoscopic radical prostatectomy with Martius fat pad flap interposition: a proposal of a new technique
Radiation therapy to the pelvis, commonly used for cervical, rectal, or prostate cancers, is another recognized trigger. Radiation can weaken tissue over months or years, eventually leading to fistula formation long after treatment ends. Foreign bodies in the bladder, whether from self-insertion, migration of surgical materials, or penetrating injuries, can also set up chronic inflammation that erodes into neighboring organs.10PubMed Central. FOREIGN BODIES IN THE URINARY BLADDER – CASE SERIES
Symptoms That Should Raise Concern
A single bubble of air during urination after a catheter change or bladder procedure is rarely worrisome. The symptoms that should prompt a visit to a doctor are those that suggest an ongoing source of gas or an accompanying infection:
- Recurrent bubbling: Air passed with urination on multiple occasions over days or weeks, rather than a one-time event.
- Foul-smelling urine: A fecal or unusually strong odor can indicate bowel contents are contaminating the bladder.
- Particles in urine: Visible debris or discoloration pointing to fecal material, sometimes called fecaluria.
- Repeated UTIs: Chronic or recurring urinary tract infections, especially with unusual bacteria, can be a clue that the urinary system is exposed to bowel organisms.
- Blood in urine: Hematuria alongside pneumaturia strengthens the suspicion of a fistula or malignancy.
- Abdominal or pelvic pain: Persistent discomfort, particularly in the lower left abdomen, may point toward diverticulitis as the underlying cause.
Because a fistula provides a direct route for stool bacteria to reach the bladder, urinary infections in fistula patients tend to be stubborn and keep coming back even with antibiotics. If you have been treated for multiple UTIs that do not seem to stay gone, and especially if you also notice gas or odd smells during urination, mentioning this pattern to your doctor can help steer the workup in the right direction.
How Doctors Figure Out the Cause
CT scanning is the go-to imaging tool for evaluating pneumaturia. It can reveal air inside the bladder, thickening of the bladder or bowel wall, the fistula tract itself, and any associated abscess or tumor. In one study focused on diverticular-related colovesical fistulas, CT accurately predicted the presence and location of the fistula in eight of nine patients and provided additional findings that helped guide surgical planning.11The Journal of Urology. Accuracy of Computerized Tomography in the Diagnosis of Colovesical Fistula Secondary to Diverticular Disease CT is also what distinguishes emphysematous cystitis from a fistula. When gas appears within the bladder wall itself rather than just floating in the bladder cavity, infection is the more likely explanation.
Colonoscopy and cystoscopy are often used alongside CT. Colonoscopy lets the doctor inspect the colon for diverticula, tumors, or inflammation. Cystoscopy, in which a small camera is inserted into the bladder, can sometimes reveal the fistula opening or areas of redness and irritation on the bladder wall. Neither test catches every fistula, though, because these openings can be tiny and intermittent.
There is also a surprisingly low-tech option: the poppy seed test. A patient swallows a measured amount of poppy seeds, and their urine is collected over the following hours. If poppy seeds show up in the urine, there must be a connection between the gut and the bladder. The test has been shown to identify colovesical fistulas with high sensitivity and is considered an accurate, convenient, and inexpensive first-line option.12PubMed. The poppy seed test for colovesical fistula: big bang, little bucks! 13PubMed Central. Reviving the poppy seed test for the diagnosis of colovesical fistula: A case report from a single rural center experience It is particularly useful in rural or resource-limited settings where advanced imaging might not be immediately available. Keep in mind, though, that a positive poppy seed test confirms a fistula exists but does not reveal the underlying disease causing it, so imaging is still needed afterward.
Treatment Depends Entirely on the Cause
If the pneumaturia is caused by emphysematous cystitis, the treatment is medical: aggressive antibiotics (often intravenous at first), blood sugar control in diabetic patients, and sometimes bladder drainage with a catheter to help the inflamed wall heal. Surgery is reserved for cases that do not respond to antibiotics or where the bladder wall has been severely damaged.
For fistulas, surgery is the definitive solution in the vast majority of cases. A systematic review and meta-analysis of enterovesical and colovesical fistula outcomes found that about three-quarters of patients underwent a single-stage operation, meaning the fistula and its cause were both addressed in one surgery. A smaller proportion required multi-stage procedures, and a few percent received palliative surgery only, typically when the fistula was caused by advanced cancer that could not be fully resected.14PubMed Central. Indications and outcomes of enterovesical and colovesical fistulas: systematic review of the literature and meta-analysis of prevalence The bladder repair itself was relatively straightforward in most cases, with simple closure used in over 80% of patients.
What the surgery involves depends on the disease behind the fistula. For diverticular disease, surgeons typically remove the affected segment of colon and repair the bladder wall. For Crohn’s disease, the surgical approach considers the wider pattern of intestinal inflammation and may be combined with medication adjustments to control the disease. For cancer, the extent of the resection depends on staging and may require removal of part of the bladder as well.
A small number of fistulas, particularly those related to Crohn’s disease, can sometimes be managed or reduced with medications (immunosuppressants or biologic therapies) rather than surgery. This is not curative in most cases, but it can be appropriate for patients who are poor surgical candidates or who have widespread disease that makes surgery high-risk.
Pneumaturia in Children
Although the vast majority of pneumaturia cases occur in middle-aged and older adults, it can rarely appear in children. When it does, the causes are usually quite different. Congenital anomalies, structural abnormalities present at birth, are the primary consideration. One reported case involved an infant with pneumaturia and fecaluria caused by a rare rectal duplication that had formed a fistula to the urethra.15The Journal of Urology. Tubular Duplication of the Rectum with a Rectourethral Fistula While these congenital causes are uncommon, the lesson is that pneumaturia in a child is never normal and always warrants investigation.
In older children and adolescents, trauma to the pelvic area (from accidents, for instance) is another possible mechanism for air entering the urinary tract, though this is usually obvious from the clinical context. Emphysematous cystitis is exceedingly rare in children because they are far less likely to have the diabetes-driven metabolic conditions that fuel gas-forming infections.
When Bubbles Are Not Pneumaturia
It is worth distinguishing true pneumaturia from something far more benign: the foamy or bubbly appearance of urine that many people notice from time to time. When urine hits the toilet water, it can trap air and create surface bubbles, especially if you are well-hydrated and urinating forcefully. This is normal and has nothing to do with gas inside the bladder. True pneumaturia feels different. People often describe a distinct sputtering or crackling sensation as gas passes through the urethra, and the air bubbles tend to rise visibly from the urine stream rather than forming on the water surface after impact.
Persistently foamy urine (not bubbly from splashing, but actually frothy like soap) is a separate concern that can point to protein in the urine, a possible sign of kidney problems. This is unrelated to pneumaturia but is another urine change worth mentioning to a doctor if it persists.
Who Is Most at Risk
Certain groups face a higher likelihood of developing the conditions that cause pneumaturia. For fistula-related pneumaturia, the biggest risk factor is age: diverticular disease becomes dramatically more common after 50, and most colovesical fistulas occur in older adults. Men are affected by colovesical fistulas more often than women, likely because the uterus sits between the colon and bladder in women and acts as a physical barrier. Women who have had a hysterectomy lose that protective buffer and have risk levels closer to men’s.
People with longstanding Crohn’s disease, especially those with ileal involvement, carry an ongoing risk of fistula formation that persists for years. For emphysematous cystitis, poorly controlled diabetes is the dominant risk factor. Immunosuppression from any cause, whether from medications, HIV, or other conditions, also raises the risk of gas-forming urinary infections. And anyone who has undergone major pelvic surgery or pelvic radiation therapy has a modestly elevated risk of developing a delayed fistula, sometimes appearing months or even years after the original treatment.
If you notice air bubbles passing with your urine more than once, or if you have any of the accompanying symptoms listed earlier, the most useful thing you can do is describe the symptom clearly to your doctor. Pneumaturia is not a term most people know, so simply saying “I’m passing gas when I pee” or “there are bubbles coming from my urethra” communicates the same information and will point the workup in the right direction.