What If Everything We Thought About Endometriosis Was Wrong?

The science, stories, and species showing what’s been missing all along.

A shadow silhouette of a women in a room, standing in front of a window with sun shinning in.

Endometriosis is too often boxed in as “a woman’s disease.” This oversimplified view not only misleads science, it erases the lived reality of countless others. Decades of evidence, from peer-reviewed case studies to deeply personal accounts, reveal a far more complex truth: endometriosis also affects cisgender men, children, fetuses, postmenopausal individuals, intersex people, transgender and nonbinary individuals – and even animals.

By tethering endometriosis exclusively to cisgender women, the medical establishment has long ignored its full biological complexity. This narrow framing has led to widespread misdiagnosis, systemic bias, delayed treatment, and lifelong consequences for those who don’t fit the mold.

Prevalence statistics, as they currently stand, reflect only those formally diagnosed, most often limited to reproductive-age women. These numbers fail to capture the many who are left out of care entirely due to inadequate research, lack of trained specialists, and restrictive diagnostic protocols that still rely on surgical confirmation and histopathology. Globally, these tools are not only inconsistently applied – they're often inaccessible.

As a result, entire populations – men, children, intersex, trans, nonbinary, and postmenopausal individuals – are routinely overlooked and excluded from both data and treatment. When factoring in cases of unexplained infertility, missed diagnoses, and disease found incidentally or outside of gynecological settings, emerging data and expert suspicion suggest a staggering truth: the real global prevalence of endometriosis may exceed one billion people.

We bring together decades of scientific literature, community testimony, and long-ignored case studies to argue a simple but urgent truth: endometriosis is a biological disease. It is not a gendered one – and it’s time for science, medicine, and society to evolve accordingly.

While some studies still reference retrograde menstruation as a possible explanation, many now favor embryonic development and coelomic metaplasia theories. Regardless of the proposed mechanism, one fact remains clear — pathology is what confirms the presence of endometriosis, usually through detection of endometrial stroma or glands.

It’s important to understand if a pathologist doesn’t see it, that doesn’t mean it wasn’t there. Small or degraded samples, fibrotic tissue, or atypical presentation may obscure detection. Like fingerprints, pathologists often rely on pattern recognition and histological inference. In fact, some lesions lose their glandular structure over time, turning into fibrosis — causing further damage while hiding the root cause.

Atypical endo, fibrotic lesions, or glandless stroma are still endo—and often go uncounted due to rigid criteria. Without broader definitions and better diagnostic access, we continue to mislabel, mistreat, and marginalize millions of people with this disease.

Endometriosis in Men

Endometriosis in cisgender men has been documented in medical literature for nearly a century. While some cases are linked to men undergoing estrogen therapy, often for prostate cancer, a growing subset occurs spontaneously, without any hormone intervention. These rare but significant cases challenge long-held assumptions that endometriosis is purely hormonally driven or exclusively tied to menstruation.

One case involved a 52-year-old man whose inguinal endometriosis was discovered incidentally during hernia surgery – he had never received hormone therapy. Another, a 79-year-old man with no history of estrogen exposure, was diagnosed with endometrial carcinoma, raising the possibility of congenital or developmental origins. A more recent 2018 report confirmed the presence of hormone receptor-positive endometrial tissue in a cisgender male with no known risk factors.

More than a dozen such cases have been documented across the U.S., Japan, Iceland, and beyond. Some involve Persistent Müllerian Duct Syndrome or intersex traits, but not all. Patients have ranged from elderly to adolescent. Many were overlooked for years or misdiagnosed entirely.

Beyond the medical journals, community stories echo this reality, sometimes more powerfully than data can. 

One woman from our community shared a multi-generational story that connects endometriosis and related conditions across both sides of her family. She grew up hearing whispers about her grandmothers’ surgeries, during which doctors reportedly discovered tissue they described as simply “female in origin.” Years later, her uncle began experiencing severe pelvic pain and underwent surgery that revealed “endometrial stroma” on his ureter and kidney tissue, usually associated with the “female origin” endometriosis pathology. He recalled that her grandmother had been diagnosed with endometriosis at 78 years old after it ruptured her sigmoid colon. Her grandmother’s twin brother had died from prostate cancer, and her great-great-grandmother had died from a rectal rupture, which was labeled as cancer, with no pathology.

Image of Uncle who had endo, holding our anon endo community member as a baby, with a smile.

This was just one side of the family.

On her father’s side, a similar pattern emerged. Her father had a history of prostate, ovarian, and breast cancers in the family tree, and he himself developed chronic urinary tract pain, bladder spasms, and worsening diarrhea as he aged. Doctors gave him antibiotics without testing, dismissing his concerns. When a prostate lump was found, he was pressured into surgery by an inexperienced urologist. The aftermath left him with lifelong complications and a severely diminished quality of life.

An image of the father of our anon endo community member, black and white style with glasses in and a suit and tie.

Years later, when she was finally diagnosed with endometriosis herself, it all clicked: the recurring pain, the misdiagnoses, the unexplained symptoms across her family – they were all part of the same invisible thread. Her story alone speaks to the devastating consequences of misattribution, gender bias, and generational gaslighting. It highlights the urgent need to see endometriosis through a broader, more inclusive lens.

Another recent and raw account comes from an anonymous community mother who believes her 40-year-old son may have prostate or perirectal endometriosis. He has a persistent cyst, ongoing pain, and urologic symptoms, but has been repeatedly dismissed by specialists. She sees his struggle through the lens of her own endometriosis journey.

And she’s not alone. A recent community-based data project – SATIREV: Project 514/415 Lived Experiences – collected at least one report of a male relative who passed away with confirmed endometriosis. These cases and stories force us to confront a painful truth: When disease is gate kept by gender, people suffer silently, and alone.

Endometriosis in Trans, Non-Binary, and Intersex

Modern research and lived experience confirm what many already know: endometriosis does not discriminate by gender identity, hormonal profile, or anatomy. Yet, the medical system often does.

Many transgender men continue to report pelvic pain, severe cramping, gastrointestinal distress, and cyclical symptoms, despite being on long-term testosterone therapy. For some, endometriosis is discovered during gender-affirming hysterectomy procedures. Surgeons are often surprised to find active lesions, having wrongly assumed the disease would be “dormant” or resolved by testosterone or hormone adjustments.

In reality, studies show that up to 30% of transmasculine individuals undergoing hysterectomy have visible, biopsy-confirmed endometriosis. These findings expose not just clinical gaps but fundamental misunderstandings about how endometriosis behaves in the body.

One powerful voice in the community is Kits Blanc – widely known on TikTok and Instagram as @KitsBlanc, or by his hashtag #KingOfEndo. A trans man living with stage 4 thoracic, diaphragmatic, sciatic, and bowel endometriosis, Kits has publicly documented his medical journey and struggle to access care. After years of dismissal and misdiagnosis, he is currently fundraising for a complex, multi-specialist surgery at the Center for Endometriosis Care in Atlanta. His story puts a human face on what medicine still refuses to see: endometriosis exists – and thrives – outside the gender binary.

Though rarer and less researched, there are increasing anecdotal and clinical accounts of trans women developing endometriosis-like symptoms. While more data is needed, the mechanism is biologically plausible: endometriotic tissue is estrogen-sensitive and can produce its own estrogen in a self-sustaining loop. For trans women receiving hormone therapy, this could theoretically activate or influence the growth of such tissue, especially in cases of residual Müllerian structures or surgical tissue displacement. 

Endometriosis has also been documented in individuals with intersex variations. These include people with Müllerian duct remnants, ambiguous or complex gonadal structures, and other variations in reproductive anatomy. In such cases, the presence of endometriotic lesions reinforces what researchers have long theorized: that endometriosis has developmental and embryonic roots, not simply a menstrual cause.

Despite all this, medical bias, knowledge gaps, and stigma continue to render transgender, nonbinary, and intersex individuals invisible in diagnostic criteria, research priorities, and clinical education.

Too many are told:"You can’t have endometriosis, you don’t even have a uterus." Too many suffer silently because their anatomy or identity doesn’t match a flawed medical script. It’s not enough to say the disease doesn’t discriminate. Our science, systems, and care must stop doing so too.

Endometriosis in Postmenopausal Individuals

It’s a common myth – especially among clinicians – that menopause “cures” endometriosis. But mounting evidence tells a different story.

As noted in the anon community account previously, one woman’s grandmother was diagnosed at 78 years old, after endometriosis ruptured her sigmoid colon. She had long since stopped menstruating and had never undergone hormone replacement therapy. Hers is not an isolated case.

A photograph of an eldery couple, a man in a gray suit and a women in a red, dressy overcoat.

Spontaneous and recurring endometriosis has been documented in postmenopausal individuals around the world. In some cases, lesions are discovered incidentally during unrelated surgeries or in the aftermath of acute emergencies – like bowel obstructions, ruptures, or severe pelvic adhesions.

These findings suggest a critical and often overlooked truth: endometriosis is not solely driven by menstruation. Rather, it likely originates from developmental misplacement of tissue during fetal growth. Menstrual hormones may influence symptom expression and inflammation, but they are not the cause.

Some researchers believe that in postmenopausal patients, estrogen produced locally by endometriotic lesions or even adipose tissue may help sustain disease activity. Others point to the immune system’s failure to eliminate misplaced cells as a contributor. Postmenopausal endometriosis seems to expose patients to a higher risk of malignant transformation.

Regardless of the mechanism, the implication is clear: Menopause does not eliminate endometriosis.

These are not fringe cases. They are stark reminders that gendered assumptions – like associating endometriosis only with menstruating, reproductive-age women – leave too many people misdiagnosed, ignored, and harmed. Postmenopausal endometriosis challenges the old framework and demands we move toward one that recognizes the lifelong, systemic nature of the disease.

Endometriosis in Fetuses and Children

Perhaps the most groundbreaking challenge to the traditional understanding of endometriosis comes from research documenting endometriosis-like lesions in human fetuses. Multiple studies have confirmed the presence of endometrial tissue in fetuses who were never exposed to menstruation – raising powerful questions about how, when, and in whom this disease begins.

• Signorile et al. (2010) discovered endometriotic lesions in 9 out of 101 fetal autopsies.

• FertilityandSterilityVol.103,No.1.(2015) reported a rare case of endometriosis diagnosed in a newborn after a large pelvic mass was discovered in utero at 35 weeks’ gestation. Surgical excision after birth confirmed hormonally active endometriotic tissue — demonstrating that endometriosis can develop before puberty or menstruation, and possibly even before birth.

These findings directly challenge the long-dominant retrograde menstruation theory, which claims endometriosis results from menstrual blood flowing backward through the fallopian tubes into the pelvic cavity. While this may explain some pelvic cases, it fails to account for lesions found in fetuses, in individuals without menstruation, in distant organs, or in those without uteruses at all.

Despite this, many doctors still tell patients – especially children – that “endometriosis can’t happen before menstruation.” But growing clinical and personal evidence says otherwise. Endometriosis has been biopsy-confirmed in children as young as eight. One case involved a 10-year-old girl with severe pelvic pain. She had never menstruated, yet laparoscopic surgery revealed active endometriotic lesions.

Community experiences mirror these findings. One mother described how her daughter began screaming in pain at just nine years old. Doctors dismissed it as “early period cramps.” By age 12, she was in emergency rooms almost monthly. It wasn’t until age 14 , after years of misdiagnosis, that she was finally diagnosed with Stage III endometriosis.

Another patient reflects on her own journey, now recognizing the signs that began long before she had a name for them:

“My symptoms began when I was 8 or 9 years old...I was passing out randomly, had stomach pain, and underwent GI scopes that only showed inflammation. I was basically told nothing was wrong...By high school, I was still passing out more often, with pain that sent me to the ER for possible appendicitis. Eventually, they found cysts on my ovaries, but I was told they were ‘just part of becoming a woman’ and would go away on their own.”

A blonde hair little girl around the age of 8 or 9 smiles for a school picture with a blue background and a dress with multiple horses on it.

These early encounters with pain and dismissal take a long-term toll. For many children and teens, endometriosis is not just a reproductive issue—it’s a life-altering disease that begins in formative years, disrupting education, self-image, relationships, and mental health.

“I almost gave up on life, but I kept going thanks to those who believed me and saw the pain for what it really was, debilitating.”

Too often, these children are misdiagnosed with anxiety, IBS, or “just bad periods.” They are prescribed psychiatric drugs, placed on birth control without diagnosis, or dismissed entirely – sometimes for a decade or more.

The existence of endometriosis in children and fetuses provides crucial proof: Endometriosis is not a disease that begins with menstruation. It is a developmental condition, influenced by – but not dependent on – hormonal cycling. Until medicine accepts this truth, countless children will continue to suffer needlessly, their lives disrupted before they even understand what’s happening to them.

Endometriosis in Animals

Endometriosis is not unique to humans. Evidence of the disease has been observed in multiple mammalian species, especially primates and domestic animals, providing strong biological confirmation that this is a naturally occurring, systemic condition rooted in biology, not behavior or gender.

• Primates: Macaques and baboons have been documented to spontaneously develop lesions identical to those seen in humans, including deep infiltrating and ovarian forms (Human reproduction update vol. 8,1 2002; Vet Pathol. 2012).

• Dogs: True spontaneous endometriosis in a non-menstruating female dog, confirming lesions without external hormones or menstruation.

• Guinea pigs: A 2017 case report confirmed endometriosis in a guinea pig presenting with adhesions and histologically verified lesions, despite no hormonal manipulation.

A tiny squirrel is wrapped up, sleeping in a dark blanket with the words "each little life...is big to the one living it" on the image.

Among the most compelling public stories is that of Little Thumbelina, an Eastern Grey Squirrel rescued as a newborn after her nest was destroyed in a high-rise apartment building. Raised by certified wildlife rehabilitators, Thumbelina showed developmental differences from the start: delayed eye opening, refusal to eat solid food, clumsiness, and an aversion to other squirrels.

Veterinary assessments revealed a complex hormonal imbalance. By 2018, she was diagnosed with Polycystic Ovarian Syndrome (PCOS), endometriosis, and an enlarged uterus. Her caregivers opted for a full hysterectomy to relieve her swelling and pain. Though she still struggles with endocrine issues, Thumbelina has since returned to a more playful and active state, loved by a growing online community.

Her journey, shared through LittleThumbelinaGirl.com, is more than just endearing, it’s eye-opening.

Thumbelina reminds us that endometriosis is not a psychosocial construct. It is not bound by gender identity or even species. When a squirrel—never menstruating, never exposed to artificial hormones, can develop the disease, we are faced with an undeniable truth:

Endometriosis is a biological disease. Full stop.

These cross-species observations dismantle any lingering doubt that endometriosis is “caused” by menstruation or modern human lifestyle. Instead, they underscore the urgent need for research that recognizes endometriosis as a systemic, inflammatory, and embryologically rooted disease, affecting bodies across the entire animal kingdom.

When Biology Meets Bias

The only reason we know of any documented cases of endometriosis outside of cisgender women is because someone was properly trained to recognize it or because pathology happened to catch it by chance. That’s it.The data doesn’t exist because the disease is rare in these populations. It exists because we rarely look. 

The math is simple: if we don’t have trained surgeons and pathologists looking for endometriosis outside of its narrow, reproductive framing, we will not see it reflected in the data. And right now, there are only a few hundred truly skilled endometriosis excision specialists in the entire world, serving a narrow-lensed population estimated to exceed 200 million. That’s just those who are diagnosed. The true number, including those still suffering in silence or never diagnosed at all, is likely far higher – possibly over a billion.

Pathology was able to detect endometriosis in some men only because they were already undergoing unrelated procedures – cancer screenings, hernia repairs, or tumor removals. Their lesions were not suspected; they were discovered incidentally, then confirmed. That is precisely why most published male cases exist, because someone took the time to look.

So what would happen if we truly began looking outside the rigid boundaries of menstruation-based assumptions? It would change everything. 

Instead of curiosity, we’re often met with public and professional denial. Rooted in outdated frameworks, institutional bias, and gender essentialism. This bias isn’t just academic—it’s public, personal, and persistent. Endometriosis is routinely denied in children because they’re seen as “too young,” in men because “they don’t have a uterus,” and in postmenopausal individuals because “they’re no longer cycling.”

But the disease doesn’t care about age, hormone levels, or assigned sex. It’s a whole-body, inflammatory condition, and when we let bias dictate where and how we look for it, we feed into the very discrimination that’s harmed generations of sufferers, especially women.

If children with confirmed endometriosis are dismissed as “too young to count,” as if their age makes their pain less real. Is that supposed to be lucky for them? Are their numbers too small to matter? Do they not deserve care because they haven’t suffered long enough? If trans and intersex people are ignored because their pain doesn’t fit outdated gender models, what are we saying? That their pain is less valid? That their bodies are less worthy of care?

On TikTok, Facebook, and other public forums, those who share their stories of endometriosis outside the “expected” narrative are routinely mocked, gaslit, and dismissed. Common comments include:

• “Men don’t have a uterus. Endo in men isn’t real.”

• “Trans men are just confused women, of course they get cramps.”

• “There’s no scientific proof unless it’s from a doctor I trust.”

• “You’re just Googling stuff, you’re not credible.”

Some openly admit they won’t believe endometriosis exists in men or gender-diverse individuals unless a doctor personally tells them. Ironically, they often quote Google while accusing others of misinformation, highlighting just how shallow our collective understanding still is.

Kits Blanc, mentioned previously – publicly sharing his battle with stage 4 endo as a trans man – faces an avalanche of ignorance online. People regularly comment:

• "You're a woman, bro. Men don’t get that."

• "You're taking away from real women who suffer."

• "You gave yourself endo with hormones, it’s your fault."

• "Impossible. Endo is a uterus disease, and men don’t have one."

These attacks aren't just cruel, they deny verified medical evidence. They reflect the same dogma that caused this disease to go misunderstood for over a century.

When people speak out – cis men, intersex individuals, postmenopausal women, trans men, children – they’re often shut down. Not for lack of evidence, but because their suffering doesn’t match our expectations. We must change how we perceive endometriosis, not just as a “woman’s reproductive disease,” but as the systemic, inflammatory, and biologically complex condition that it truly is.

The Cost of Exclusion

The consequences of dismissing endometriosis as a narrowly defined “women’s reproductive disease” are not theoretical – they’re catastrophic.

People across the gender spectrum are suffering in silence because their pain doesn’t “fit” outdated criteria. Children are left untreated because they’re seen as “too young.” Postmenopausal people are ignored because they’re “done cycling.” Trans and nonbinary people are denied not only treatment, but recognition of their humanity. And countless cisgender women are still told their symptoms are normal, hysterical, or irrelevant.

When science evolves but systems don’t, people are left behind. When diagnosis depends on outdated assumptions, people die waiting. And when we refuse to see endometriosis for what it truly is – a systemic disease affecting diverse bodies – we become complicit in the harm.

This isn’t just about awareness. It’s about accountability.

The cost of exclusion is measured in delayed diagnoses, denied care, misattributed deaths, fractured families, and lives permanently altered by preventable damage. It is measured in surgeries that never should have happened, and in cancers missed because someone decided it “couldn’t be endo.”

We are standing at a critical public health crisis crossroad. To truly address endometriosis as the complex, systemic disease it is, we must act boldly and inclusively. That begins by rejecting the old narrative and embracing a future rooted in truth, equity, and science.

Our refusal to acknowledge the disease’s true reach has caused real, measurable, generational harm. As one community advocate said it best:

“Endometriosis doesn’t care how you identify. It doesn’t wait for your period. It doesn’t respect your gender marker. It’s time the medical system stopped pretending otherwise.”

Endometriosis doesn’t whisper. It screams. It bleeds into generations, bodies, and broken systems. We’ve carried this disease in silence for too long, while bias wrote our medical textbooks and our pain was dismissed as imaginary. It’s time to rewrite the story with every voice that’s been left out of the room.

We owe it to ourselves, and to the ones still waiting in the dark, to finally listen.