Prolapse in dogs happens when an internal organ or tissue pushes out of its normal position, often becoming visible outside the body. The most common types are rectal, vaginal, urethral, and uterine prolapse, and each has distinct causes. The single biggest driver across nearly all types is straining, whether from digestive problems, difficult labor, or breathing difficulties that increase pressure inside the abdomen.
Rectal Prolapse
Rectal prolapse, where part of the rectal lining pushes out through the anus, is the type most dog owners encounter. The underlying cause is almost always prolonged straining. Anything that makes a dog push hard and repeatedly can trigger it.
Internal parasites are one of the most common culprits, especially in puppies. Parasitic infections like coccidia cause severe diarrhea and tenesmus, a painful, involuntary spasm of the muscles around the anus that drives the dog to strain continuously. That repeated pressure eventually forces the rectal tissue outward. Other intestinal parasites, including hookworms and whipworms, can produce the same cycle of diarrhea and straining.
Beyond parasites, rectal prolapse can result from colitis, dietary changes that cause persistent diarrhea, constipation, or any condition affecting the lower bowel. Tumors or polyps in the colon and rectum can also cause chronic straining. Puppies and young dogs are more vulnerable because their immune systems are still developing, making them more susceptible to the parasitic and infectious causes that drive straining. In older dogs, masses or inflammatory bowel conditions are more typical triggers.
Once the tissue protrudes, it initially appears swollen, pink, and inflamed. If it isn’t addressed, the exposed tissue dries out, darkens, hardens, and can become necrotic. That progression can happen within hours to days depending on the severity, so visible rectal prolapse always requires prompt veterinary attention.
Vaginal Prolapse
Vaginal prolapse in dogs is driven primarily by hormones, specifically estrogen. During proestrus and estrus (the phases leading up to and including heat), a sharp rise in estrogen levels causes the vaginal tissue to swell with increased blood flow and fluid. In most dogs this swelling stays internal, but in some, the tissue becomes so engorged that it bulges out through the vulva.
The degree of swelling tracks directly with estrogen levels. Research measuring serum estrogen in affected dogs found that breeds with higher estrogen concentrations during heat developed more severe tissue changes, including ulceration and inflammation of the vaginal lining. The condition typically regresses on its own once the dog enters the luteal phase (the stage after heat when estrogen drops), but it tends to recur with each subsequent heat cycle and can also develop after giving birth.
Large and giant breeds appear more prone to vaginal prolapse. Certain breeds like Mastiffs and Cocker Spaniels have shown more severe tissue changes in clinical studies. True vaginal prolapse, where the full vaginal wall turns inside out, is rarer and is occasionally seen in dogs with constipation, difficult labor, or forced separation during mating.
Urethral Prolapse
Urethral prolapse, where the lining of the urethra protrudes from the tip of the penis, is one of the more breed-specific types. English Bulldogs are overwhelmingly predisposed. In one retrospective study, English Bulldogs had an odds ratio of roughly 367 compared to all other breeds, making them hundreds of times more likely to develop this condition. In that same study, 65% of all affected dogs were English Bulldogs, and 80% were either a brachycephalic breed (English or French Bulldog) or had documented signs of brachycephalic obstructive airway syndrome (BOAS).
The connection to breathing problems is the key piece. Brachycephalic dogs struggle to move air through their shortened airways, and the extra respiratory effort increases pressure inside the abdomen. That pressure impairs blood drainage through the veins around the urethra, causing the spongy tissue surrounding it to become engorged and eventually push outward. Yorkshire Terriers, which are prone to collapsing trachea, face a similar mechanism: labored breathing creates the same intra-abdominal pressure spikes.
Other proposed contributing factors include urinary tract infections, urinary stones, excessive sexual behavior, and gastrointestinal problems that cause vomiting. Essentially, any condition that repeatedly forces the dog to bear down or struggle to breathe can play a role. The condition almost exclusively affects intact males.
Uterine Prolapse
Uterine prolapse occurs when part or all of the uterus turns inside out and protrudes through the vulva. It happens during or immediately after giving birth, and it is rare in dogs compared to some other species.
The primary risk factors center on complications during labor. Prolonged dystocia (difficult or obstructed labor) leaves the uterus exhausted and weakened from sustained contractions. Nutritional deficiencies, particularly low calcium, contribute to uterine inertia, where the uterus loses its ability to contract effectively. Retained fetal membranes can also trigger prolonged, ineffective contractions that push the uterus outward rather than helping it shrink back to normal size.
After birth, the uterus normally undergoes involution, a process where it contracts back down and regenerates its lining. Hormonal shifts during this period, combined with any of the risk factors above, can disrupt that process. In some cases, the contractions that cause the prolapse can also lead to intussusception of the uterine horn, where one part of the uterus telescopes into another, a life-threatening complication that requires emergency surgery.
Increased Abdominal Pressure: The Common Thread
Across all prolapse types, the shared mechanism is sustained or repeated increases in pressure inside the abdomen. In rectal prolapse, that pressure comes from straining to defecate. In urethral prolapse, it comes from labored breathing. In uterine prolapse, it comes from contractions during and after birth. In vaginal prolapse, hormonal swelling combines with any additional straining from constipation or labor.
This is why seemingly unrelated conditions can all lead to prolapse. A dog with chronic vomiting, a puppy with a heavy parasite load, a Bulldog with narrowed nostrils, and a mother dog with a calcium-deficient diet are all experiencing different versions of the same biomechanical problem: too much force pushing outward against tissue that can’t resist it.
Which Dogs Are Most at Risk
Age, breed, and reproductive status all influence prolapse risk. Puppies are especially vulnerable to rectal prolapse because they’re more likely to develop heavy parasitic infections and the severe diarrhea that follows. Intact female dogs are at risk for vaginal prolapse during every heat cycle, and the condition often worsens with successive cycles. Dogs giving birth for the first time, or those with a history of difficult deliveries, face higher uterine prolapse risk.
Breed predisposition is strongest for urethral prolapse. English Bulldogs, French Bulldogs, American Pit Bull Terriers, and Yorkshire Terriers all carry elevated risk. For vaginal prolapse, large and giant breeds are more commonly affected. Rectal prolapse does not show as strong a breed pattern because its causes (parasites, dietary issues, bowel disease) cut across all breeds.
What Happens Without Treatment
Any prolapsed tissue that remains exposed outside the body is at risk of drying out, swelling further, and losing blood supply. With rectal prolapse, the visible tissue initially looks red and swollen but progressively darkens and hardens as circulation is cut off. Necrotic (dead) tissue cannot be saved and must be surgically removed rather than simply pushed back into place.
The speed of this progression depends on the type and severity of the prolapse, but the direction is always the same: exposed tissue deteriorates over time. Keeping the tissue moist and getting veterinary help quickly gives the best chance of a simple, non-surgical resolution. When the underlying cause (parasites, airway obstruction, hormonal cycling) isn’t also addressed, prolapse is likely to recur even after successful treatment.