Why Does Bowel Endometriosis Cause Digestive Problems?

If you've been told your digestive symptoms are IBS — or stress, or just part of having a sensitive stomach — and you know in your body that's not the whole story, you're probably right.

For a significant portion of people with endometriosis, the disease doesn't stay in the pelvis. It grows into the bowel wall. Not as a figure of speech — the endometrial-like tissue physically infiltrates the layers of the intestine, and when it does, it changes how your bowel moves, contracts, bleeds, and behaves. Your gut symptoms aren't separate from your endo. They are your endo.

This article is for anyone who has ever left a GI appointment feeling unheard, who has been handed an IBS diagnosis after a normal colonoscopy, or who knows that the pain they feel during bowel movements is not normal — and needs the language and the evidence to go back to their doctor and say so.

What is bowel endometriosis, exactly?

Bowel endometriosis is a specific type of deep infiltrating endometriosis (DIE) — meaning the disease has grown deep into the tissue rather than sitting superficially on the surface of organs. In bowel endo, endometrial-like tissue penetrates into the wall of the intestine, most often the rectosigmoid colon (the lower section of your colon, just above the rectum). [1]

Estimates of how common this is vary quite a bit — from around 3% of all women with endometriosis to as high as 37%, depending on the population studied. But in women who are already known to have deep endometriosis and are being imaged by specialists, that number climbs to 43.6%. [4,5] So if you have confirmed deep endo and you have gut symptoms, there is a real and substantial chance the two are connected.

The defining feature of bowel endometriosis is that the tissue has grown at least into the muscularis propria. Let's break that down. Your bowel wall has layers, kind of like an onion:

• The serosa is the outermost covering — the skin of the bowel.
• The muscularis propria is the muscle layer underneath. This is what makes your bowel contract and push things through (called peristalsis). Without it working properly, nothing moves the way it should.
• Below that is the submucosa, a connective tissue layer.
• And the innermost layer is the mucosa — the actual lining.

In bowel endometriosis, the disease has gotten past the surface and into the muscle. In some cases it goes deeper. A 2025 histological study of surgically removed bowel specimens found that 94% showed involvement of the muscularis propria, and 78% showed smooth muscle hypertrophy — meaning the muscle cells had enlarged in response to the infiltration. [15] That structural change is why the bowel doesn't function normally. The architecture itself has been disrupted.

The symptoms your doctor might be misreading

There are three symptoms that, when they appear together and follow your menstrual cycle, should immediately put bowel endometriosis on the table.

Painful bowel movements (dyschezia)

Dyschezia — painful defecation — is present in approximately 37.5% of people with confirmed bowel endometriosis. [11] That makes it one of the most specific symptoms for rectosigmoid involvement. The pain typically worsens one to two weeks before your period, when inflammation is ramping up, and often improves once bleeding starts.

If going to the bathroom hurts more right before your period than at other times of the month, that pattern is clinically meaningful. It's not IBS. IBS doesn't track with your cycle like that.

Rectal bleeding synchronized with menstruation

When endometrial-like tissue infiltrates all the way to the mucosa — the inner lining of the bowel — it can bleed during menstruation, just like the tissue in your uterus does. This produces bloody stools or bloody discharge that appears with your period and resolves when it ends. [3] It's not hemorrhoids. It's not colitis. It's the tissue responding to the same hormonal signals that drive your menstrual bleed, but doing it inside your bowel wall.

If this is happening to you, document it and bring it to your appointment. It's a critical diagnostic finding.

Severe abdominal bloating (endo belly)

Endo belly — the abdominal distension that can make you look and feel visibly pregnant — is nearly universal in people with bowel endometriosis. A prospective study confirmed that this bloating correlates with disease activity and with motility changes in the bowel, not just with gas or what you ate. [12] It worsens in the premenstrual phase, it can be incapacitating, and it is completely disproportionate to food intake. Because it is not primarily a food reaction. It is a disease reaction.

Many people also experience alternating diarrhea and constipation that tracks with their cycle — urgency and loose stools in the days before or during their period, constipation in the middle. [1,3] This cyclical pattern is a key distinguishing feature from functional bowel disorders.

Why a normal colonoscopy doesn't clear you

This is the piece that gets people stuck for years.

A gastroenterologist scopes you, finds nothing, and sends you home with an IBS diagnosis. You feel gaslit. Here's why this happens, and why it's a limitation of the test — not confirmation that you're fine.

Colonoscopy looks at the inner surface of the bowel — the mucosa. But bowel endometriosis, by definition, starts in the deeper layers. In the vast majority of cases, the muscularis propria is where the disease lives. The mucosa often looks completely normal from the inside, because the disease is growing in the wall, not on the surface. [1,8]

Colonoscopy has a sensitivity of somewhere between 20-40% for detecting bowel endometriosis. [23] That means it misses it at least 60% of the time. A normal colonoscopy does not rule out bowel endometriosis. It was never designed to.

What actually finds it is a transvaginal ultrasound with bowel preparation (TVUS-BP), performed by someone with expertise in deep endometriosis imaging. In skilled hands, this achieves 83% sensitivity and 97% specificity for rectosigmoid endometriosis. [21] MRI with endorectal contrast is the next step for complex cases, achieving comparable accuracy and providing better anatomical mapping for surgical planning. [22]

A colonoscopy is appropriate to rule out colorectal cancer, inflammatory bowel disease, or polyps. But it is not the right tool for finding bowel endo. A normal result should not be used to close the door on your symptoms.

What is actually happening in your body — and why symptoms follow your cycle

There are four mechanisms driving your bowel symptoms, and understanding them helps explain why your symptoms behave the way they do.

The muscle can't do its job

The bowel moves things through via rhythmic contractions called peristalsis — waves of muscle squeezing in sequence. When endometrial-like tissue infiltrates the muscularis propria and causes the smooth muscle to enlarge and scar, that coordinated squeezing gets disrupted. [1,15] The result is partial obstruction, constipation, and sometimes paradoxical diarrhea. Some sections move too slowly. Others react erratically. Nothing is in rhythm anymore.

Your pain nerves are growing into the lesions

Endometriotic tissue doesn't just sit in the bowel wall passively. It recruits nerves. New sensory nerve fibers actually grow into the lesions themselves — a process called neuroangiogenesis, where nerve fibers and blood vessels co-grow into the diseased tissue together. [16,17] These are pain-carrying fibers. They express substance P and CGRP — molecules that transmit pain signals. So when your bowel contracts around a lesion, or when inflammation spikes before your period, those signals aren't traveling through normal pathways. They're amplified by a dense network of sensory nerves that shouldn't be there.

This is why the pain from bowel endometriosis often feels completely out of proportion to what you ate or what's happening in your gut. It's coming from sensitized pain fibers embedded in the disease, not from normal bowel function.

When this process happens repeatedly, your nervous system adapts by lowering its pain threshold. Nerve fibers embedded in bowel endo lesions send constant pain signals that, over time, train your spinal cord and brain to interpret normal stimuli as painful. This state is called central sensitization, and it explains why bowel endo pain often feels completely out of proportion to what imaging shows or what's physically happening in the gut. [31,32] Central sensitization also explains why removing the lesions surgically doesn't always eliminate the pain. If your nervous system has adapted to expect pain signals, it requires its own targeted treatment to reset, even after the original disease is gone. Pain reprocessing therapy and neuromodulation approaches can address this component when medication and surgery alone don't provide relief.

Prostaglandins are driving the cramping and diarrhea

The reason your bowel cramps explode right before your period comes down to a specific molecule your lesions are overproducing. Endometrial-like tissue is loaded with an enzyme called COX-2 (cyclooxygenase-2), which cranks out prostaglandin F2-alpha (PGF2α) at much higher levels than normal tissue. [18] PGF2α tells your intestinal muscles to contract hard and repeatedly. That's why your worst bowel days are almost always in the week before your period — prostaglandin production peaks during the luteal phase. [18,19]

NSAIDs like ibuprofen work partially on this pathway, which is why some people find them take the edge off bowel symptoms as well as pelvic pain. They don't fix the disease, but they reduce the prostaglandin-driven component. [19]

Your gut microbiome is also affected

Emerging research shows that women with endometriosis consistently have different gut microbiome compositions than women without it. Multiple studies document lower levels of protective Lactobacillus species and higher levels of Prevotella, a bacterium associated with inflammation, with the severity of dysbiosis correlating with symptom burden. [20] Whether this microbiome shift is a cause or a consequence of endometriosis is still being studied — the inflammation from endo almost certainly alters gut bacteria, but the altered bacteria may also make the inflammatory environment worse.

SIBO and bowel endometriosis: a common overlap

Small intestinal bacterial overgrowth (SIBO) — when bacteria that normally live in the colon migrate into and overpopulate the small intestine — is found in an estimated 20–30% of women with endometriosis, compared to 5–15% of healthy controls. [33] Women with bowel endometriosis are at especially high risk because lesions in or near the bowel wall alter normal intestinal muscle contractions and create an environment where bacteria can proliferate unchecked.

SIBO produces gas in the small intestine, which causes severe bloating, cramping, and alternating constipation and diarrhea — symptoms that are often misidentified as IBS. The problem is that SIBO is treatable with specific antibiotics (most commonly rifaxomicin) or herbal protocols, but this won't happen if it's never diagnosed.

If your bloating is particularly severe, or if you have significant constipation and diarrhea cycling that isn't fully explained by your endo symptoms alone, ask your provider about SIBO testing. A hydrogen and methane breath test is the standard diagnostic tool — it's simple, noninvasive, and can be done at home. You drink a sugar solution and then breathe into collection tubes at set intervals. If bacteria in your small intestine ferment that sugar prematurely, you'll have elevated hydrogen or methane levels in your breath, which is diagnostic. [33]

What the evidence supports for treatment

Medical management focuses on suppressing the hormonal cycle that drives monthly flares. Continuous hormonal contraceptives, progestins (particularly dienogest, which has specific activity in endometriotic tissue and showed significant reduction in dyschezia scores in a 2022 trial), and GnRH agonists all reduce the prostaglandin surge and inflammatory activity that cause your worst bowel days. [3,27,28] They don't remove the disease. They turn down the volume.

Dietary modifications — particularly low-FODMAP eating — can help some people with a functional overlay (IBS-type symptoms on top of endo symptoms), but they address the IBS component, not the endometriotic disease itself. [30] They're a useful addition, not the foundation.

The most durable treatment for confirmed bowel endometriosis is surgical excision by a specialist with experience in deep disease. The type of surgery depends on how deeply the lesion has infiltrated and how large it is:

• Shaving — removing the nodule from the surface while leaving the bowel wall intact, appropriate for lesions confined to the outer layers
• Disc excision — removing a full-thickness disc of bowel wall around the lesion, for nodules smaller than about 3 cm
• Segmental resection — removing a section of the bowel entirely and reconnecting the ends, required for large, multifocal, or deeply obstructing disease

A 2024 randomized trial found no significant difference in long-term digestive symptom improvement between shaving and disc excision at five years when performed by experienced surgeons. [24] Segmental resection provides the most complete disease clearance, but it carries the highest complication risk, including anastomotic leak, bladder dysfunction, and temporary stoma. [25,26] The decision between these approaches should be based on lesion size, your surgeon's expertise, and your individual goals.

What bowel endometriosis does to your pelvic floor

Deep bowel endometriosis frequently co-exists with pelvic floor hypertonicity — the muscles that surround the bowel become chronically tight and tense in response to the pain and inflammation. [34] This muscular tension isn't just a reaction to having endo pain. It becomes a problem of its own. Tight pelvic floor muscles contribute to constipation, straining with bowel movements, pain during defecation, and difficulty relaxing completely — independently of the disease itself.

This is important because surgery and medication address the endometrial lesions, but they don't address the muscular adaptation. If your pelvic floor muscles have been clenching and guarding for years in response to bowel pain, those muscles need targeted treatment to release and retrain.

Pelvic floor physical therapy that specifically addresses bowel function — including internal release techniques, myofascial release, and relaxation training — can reduce symptoms that surgery and hormonal medication often miss. [34,35] Many women with bowel endo benefit from a combination approach: medical or surgical management of the disease itself, plus pelvic floor PT to address the muscular component. You deserve both.

What bowel endometriosis does to intimacy

Bowel endometriosis is one of the most common drivers of painful intercourse (dyspareunia) because the rectovaginal space — the tissue between your rectum and vagina — is the most densely innervated area affected by deep endo. [36] Research shows that 80% or more of women with deep infiltrating endometriosis report pain with sex, with bowel involvement specifically associated with severe dyspareunia. [36,37]

Many women stop having sex entirely, or avoid it for months around their period, without ever connecting it to bowel disease. They may feel shame, relationship strain, or assume it means something is wrong with them or their partnership. This is not a relationship problem. It is a disease symptom that deserves to be on the table with your provider.

Pain with sex from bowel endo can improve with pelvic floor PT and nerve-targeted therapies like neuromodulation or pain reprocessing, even when the primary treatment is surgical. Your ability to have pain-free intercourse matters and should be part of your treatment goals. [36,37]

What to say to your doctor

If you recognize yourself in this article and you've been brushed off, here is the vocabulary and the evidence you can bring with you.

If your bowel pain follows your cycle — worse before your period, better after — tell your doctor that cyclical dyschezia (painful bowel movements) is a specific clinical symptom of rectosigmoid endometriosis, and that a normal colonoscopy does not exclude it. Colonoscopy has 20-40% sensitivity for this disease [23] — it looks at the inner surface of the bowel, and bowel endometriosis lives in the wall. What you need is a transvaginal ultrasound with bowel preparation by a provider experienced in deep endometriosis imaging.

If your GI doctor says IBS: ask whether they have considered that your symptoms are cyclical. IBS does not track with the menstrual cycle. Endometriosis-driven bowel symptoms do — because they're being driven by prostaglandins and inflammation that peak in the luteal phase. [1,18]

If you've been told your imaging is normal, ask what imaging was done. A standard pelvic ultrasound or colonoscopy will not find bowel endometriosis. You need specialized TVUS with bowel prep or MRI with endorectal contrast, ideally at a center that sees significant deep endometriosis volume. [21,22]

You can cite this directly: the 2024 ACR Appropriateness Criteria recommend ultrasound as the initial imaging modality for suspected bowel endometriosis — not colonoscopy. [8]

You are not describing IBS. You're describing a structural disease process that has a name, a mechanism, and a diagnostic pathway. You deserve a provider who knows the difference.