What Is The Root Cause Of Endometriosis and Fibroids: What to Know

September 13, 2025

What Is the Root Cause of Endometriosis and Fibroids: What to Know

Endometriosis and uterine fibroids are among the most common gynecologic conditions, yet many people still ask: What is the root cause? The honest, science-based answer is that there is no single root cause for either condition. Both are complex, influenced by genetics, hormones, immune and inflammatory pathways, and environmental and lifestyle factors. Understanding what researchers do and do not know can help you make informed decisions about symptoms, diagnosis, and treatment.

Is There a Single Root Cause?

No. Both endometriosis and fibroids are multifactorial. Scientists have identified patterns and risk factors, but not a single trigger that explains all cases. Think of them as conditions that develop when several biological systems—hormones, genetics, immune responses, and tissue repair—interact in susceptible individuals.

Endometriosis: What We Know About Causes

Endometriosis occurs when tissue similar to the uterine lining grows outside the uterus, causing inflammation, pain, scar tissue, and sometimes fertility problems. About 1 in 10 women of reproductive age may be affected, though the true number is likely higher due to underdiagnosis.

Leading scientific theories

Retrograde menstruation: Menstrual blood flows backward through the fallopian tubes into the pelvis, seeding endometrial cells. Most people experience some retrograde flow, so this alone doesn’t explain why only some develop disease.
Coelomic metaplasia and Müllerian remnants: Cells lining the pelvis or leftover embryonic cells transform into endometrial-like tissue under certain signals.
Lymphatic/vascular spread and stem cell theories: Cells travel through lymph or blood, or arise from stem/progenitor cells, explaining disease found in distant sites.

Key biological drivers

Estrogen dependence and progesterone resistance: Endometriosis lesions often make their own estrogen (via aromatase) and respond poorly to progesterone, promoting growth and inflammation.
Immune and inflammatory dysregulation: Elevated inflammatory mediators and altered immune cell function allow ectopic tissue to implant and persist.
Genetic and epigenetic factors: Family history raises risk; multiple gene variants modestly increase susceptibility.
Environmental influences: Research is ongoing into endocrine-disrupting chemicals; evidence is mixed and not definitive.

Risk factors and patterns

Early menarche, short menstrual cycles, heavy or prolonged periods
Family history of endometriosis
Conditions that obstruct flow (e.g., congenital uterine anomalies)

Importantly, endometriosis affects people of all races and ethnicities; historical underrecognition in Black and Hispanic patients has contributed to delayed diagnoses.

Fibroids (Uterine Leiomyomas): What We Know About Causes

Fibroids are benign smooth muscle tumors of the uterus. They are extremely common—by age 50, most women have at least one, with higher prevalence and symptom burden among Black women.

How fibroids start and grow

Monoclonal origin: Each fibroid typically arises from a single smooth muscle cell that acquires mutations and then expands.
Common gene changes: Somatic mutations—especially in MED12—and alterations involving HMGA2 are frequently found. These changes influence cell growth, extracellular matrix production, and hormone sensitivity.
Hormonal and growth factor signaling: Estrogen and progesterone, along with pathways like TGF-β, promote cell growth and the accumulation of extracellular matrix that makes fibroids firm and bulky.

Risk factors and patterns

Family history, African ancestry, and age (most prominent in 30s–40s)
Early menarche, obesity, and possibly hypertension
Lower risk with childbirth and some hormonal contraceptives

Dietary patterns (e.g., higher green vegetables) and vitamin D status have been associated with risk in observational studies, but they are not proven causes.

Do Endometriosis and Fibroids Overlap?

Yes and no. They are distinct conditions—endometriosis is ectopic endometrial-like tissue; fibroids are tumors in the uterine muscle. They can coexist and share features:

Hormone responsiveness: Both are influenced by estrogen and progesterone.
Inflammation and pain: Both can inflame pelvic tissues and cause heavy bleeding, pain, and anemia.
Genetic susceptibility: Family history may cluster pelvic pain and fibroid symptoms.

However, having one does not guarantee you will develop the other.

Myths vs. Facts

Myth: Toxins are the root cause. Fact: Environmental chemicals are under study, but no single toxin explains most cases.
Myth: Sexual activity, abortions, or IUDs cause these conditions. Fact: None of these are established causes.
Myth: Pregnancy cures endometriosis or fibroids. Fact: Symptoms may change during or after pregnancy, but neither condition is reliably “cured” by pregnancy.

How Doctors Diagnose

Endometriosis: Diagnosis is based on symptoms, exam, and imaging (transvaginal ultrasound or MRI for endometriomas and deep disease). Laparoscopic visualization with or without biopsy remains the definitive method, though many are treated based on clinical suspicion.
Fibroids: Pelvic exam and ultrasound are first-line; MRI helps map size and location when planning procedures.

Evidence-Based Treatments

Endometriosis

Pain and hormonal therapies: NSAIDs; continuous combined oral contraceptives; progestins (including levonorgestrel IUD); and GnRH agonists or antagonists with “add-back” therapy to protect bone.
Surgery: Laparoscopic excision or ablation for pain, endometriomas, or infertility, especially when medications are not enough.
Fertility: Individualized plans may include surgery, ovulation suppression for pain, or assisted reproduction.

Fibroids

Watchful waiting: Appropriate if symptoms are mild and anemia is absent.
Medications: Tranexamic acid for heavy bleeding; hormonal contraceptives or levonorgestrel IUD for bleeding control. FDA-approved oral GnRH antagonist combinations can reduce bleeding and shrink fibroids (e.g., elagolix with estradiol/norethindrone; relugolix with estradiol/norethindrone).
Procedures: Uterine artery embolization, myomectomy (for those desiring fertility), MRI-guided focused ultrasound, or hysterectomy when definitive treatment is desired.

Choice of therapy depends on your goals (pain relief, bleeding control, fertility), fibroid size and location, age, and health history. Discuss trade-offs, side effects, and long-term plans with your clinician.

When to Seek Care

See a healthcare professional if you have:

Pelvic pain that interferes with work, school, sex, or daily life
Heavy periods (soaking pads/tampons hourly, passing large clots) or anemia
Infertility or recurrent pregnancy loss
New or worsening symptoms

The Bottom Line

There is no single root cause of endometriosis or fibroids. Both arise from a combination of genetic susceptibility, hormone signaling, immune and inflammatory pathways, and other modifiers. The good news: evidence-based treatments can substantially reduce pain and bleeding and support fertility goals. Partner with a clinician experienced in these conditions, and don’t hesitate to seek a second opinion if your symptoms are dismissed.