Endometriosis: Looking Beyond Hormones

Endometriosis is often described as a hormonal condition, yet the reality is considerably more complex. It is a chronic inflammatory disorder involving the immune system, nervous system, microbiome, hormone signalling pathways and environmental influences.

Whilst oestrogen plays a significant role, it represents only one piece of a much larger picture.

Endometriosis is characterised by the presence of endometrial-like tissue outside the uterus. These lesions can be found on the ovaries, fallopian tubes, pelvic peritoneum, bladder and bowel. In more unusual cases, endometrial tissue has also been identified in distant sites including the lungs, sinuses and even the ears.

The lesions respond to hormonal signals throughout the menstrual cycle, creating localised areas of inflammation that can become self-perpetuating. Over time, this inflammatory process may contribute to fibrosis, scarring, adhesions, altered pain processing and changes in tissue function

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Endometriosis Is Not One Disease

Endometriosis is a heterogeneous condition, meaning it presents differently from one woman to another.

Superficial Endometriosis

Superficial lesions are found on the surface of the peritoneum. They are often described as small, freckle-like deposits and do not deeply penetrate surrounding tissues.

Interestingly, some women with extensive superficial lesions experience very little pain, whilst others with minimal visible disease experience significant symptoms.

Deep Infiltrating Endometriosis

Deep infiltrating endometriosis penetrates more than 5mm beneath the peritoneal surface and may affect structures including:

• Bowel

• Bladder

• Ureters

• Pelvic ligaments

This form is generally associated with greater inflammation, fibrosis and organ involvement.

Endometriomas

Endometriomas, often referred to as “chocolate cysts”, are cystic structures typically found within the ovaries and filled with old menstrual blood.

Approximately 15% of women with endometriosis develop endometriomas.

Why Some Women Experience Severe Pain

One of the biggest misconceptions surrounding endometriosis is that pain directly reflects the amount of visible disease. This is not always true.

Some women with extensive lesions experience relatively little discomfort, whilst others with minimal disease experience debilitating pain.

Pain in endometriosis involves several overlapping mechanisms:

Peripheral Inflammation

Inflammatory cytokines stimulate pain-sensitive nerve endings within the pelvis.

Neurogenesis

Endometriosis lesions contain nerve fibres. As lesions develop, they promote the growth of additional nerve tissue through a process known as neurogenesis.

Central Sensitisation

Over time, the central nervous system can become hypersensitive.

This phenomenon is known as central sensitisation.

Pain pathways become amplified, meaning stimuli that would not normally be painful can trigger significant discomfort.

Allodynia

Allodynia occurs when normally non-painful sensations become painful.

Examples include:

• Light touch

• Pressure

• Certain movements

  
  

Pelvic Floor Dysfunction

Chronic pain often leads to altered movement patterns, muscle guarding and pelvic floor spasm.

The nervous system begins to anticipate pain, creating a cycle of tension, muscle dysfunction and ongoing symptom generation.

The Role of the Immune System

A healthy immune system should identify and remove misplaced endometrial tissue.

In women with endometriosis, this process appears to be impaired.

Research demonstrates:

• Reduced natural killer (NK) cell activity

• Altered macrophage function

• Chronic activation of inflammatory pathways

• Abnormal immune surveillance

The immune system becomes less effective at clearing retrograde menstrual debris whilst simultaneously maintaining a chronic inflammatory environment.

Macrophages

Macrophages play a central role in lesion survival. Early lesions are associated with inflammatory M1 macrophages. Older lesions become increasingly populated by M2 macrophages, which promote:

• Angiogenesis

• Tissue remodelling

• Lesion survival

• Neurogenesis

In essence, the very cells designed to clean up damaged tissue may inadvertently support lesion persistence.

The Oestrogen Connection

Endometriosis is considered an oestrogen-dependent condition. The lesions themselves possess increased aromatase activity. Aromatase converts androgens into oestrogen.

This creates a local oestrogen-rich environment that drives:

• Cellular proliferation

• Inflammation

• Angiogenesis

• Lesion growth

Many lesions also demonstrate increased expression of oestrogen receptor beta (ER-β), further amplifying their response to circulating oestrogen.

The Prostaglandin Cycle

One of the key inflammatory mediators in endometriosis is prostaglandin E2 (PGE2).

PGE2 stimulates:

• Aromatase activity

• Oestrogen production

• Inflammatory cytokine release

• Pain signalling

This creates a vicious cycle:

More inflammation → More prostaglandins → More aromatase → More oestrogen → More inflammation.

The cycle can become self-sustaining.

Progesterone Resistance

Progesterone normally acts as a balancing hormone.

It exerts anti-inflammatory effects and helps regulate endometrial growth. Many women with endometriosis exhibit progesterone resistance. This means the tissues become less responsive to progesterone signalling despite adequate hormone levels.

As progesterone responsiveness declines:

• Oestrogen dominance within lesions increases

• Inflammatory signalling increases

• Angiogenesis accelerates

• Lesion growth continues

This helps explain why endometriosis is not simply a matter of measuring hormone levels.

Receptor activity is equally important.

Angiogenesis: Feeding the Lesions

For lesions to survive they require a blood supply. This process is known as angiogenesis.

A key driver is Vascular Endothelial Growth Factor (VEGF). VEGF stimulates new blood vessel formation, allowing lesions to:

• Receive oxygen

• Access nutrients

• Continue growing

  
  

Increased VEGF expression is consistently observed within endometriosis lesions.

Hypoxia and Lesion Growth

When endometrial fragments implant outside the uterus they enter an oxygen-poor environment.

This creates localised hypoxia.

Hypoxia activates Hypoxia Inducible Factor 1-alpha (HIF-1α), which subsequently stimulates:

• VEGF production

• Angiogenesis

• Cellular proliferation

  
  

Hypoxia therefore becomes another driver of lesion survival.

Iron Accumulation and Oxidative Stress

Retrograde menstruation introduces blood into the pelvic cavity.

As red blood cells break down, iron accumulates.

Under normal circumstances macrophages clear this debris efficiently.

In endometriosis this process appears impaired.

The result is excessive accumulation of:

• Free iron

• Reactive oxygen species

• Oxidative stress

• Inflammatory mediators

  
  

This contributes further to tissue irritation and lesion progression.

Importantly, iron deficiency elsewhere in the body does not necessarily mean pelvic tissues are deficient in iron.

This is one reason blanket iron supplementation may not always be appropriate without understanding the wider clinical picture.

The Gut-Endometriosis Connection

Increasing research supports a connection between endometriosis and the microbiome.

Women with endometriosis frequently demonstrate alterations within:

• Gut microbiota

• Vaginal microbiota

• Endometrial microbiota

  
  

Dysbiosis and LPS

Certain bacterial populations produce lipopolysaccharides (LPS).

LPS strongly activates immune pathways via Toll-Like Receptor 4 (TLR4).

This drives:

• IL-6

• TNF-alpha

• NF-kB activation

• Chronic inflammation

The Oestrobolome

The gut microbiome also influences oestrogen metabolism.

Bacteria producing beta-glucuronidase can reactivate oestrogen that would otherwise be eliminated.

This increases recirculating oestrogen levels and may contribute to the oestrogenic environment associated with endometriosis.

Histamine and Mast Cells

Mast cells are increasingly recognised as important contributors to endometriosis symptoms.

Elevated mast cell activity has been identified within deep infiltrating lesions.

Activated mast cells release:

• Histamine

• Cytokines

• Growth factors

These compounds contribute to:

• Pain

• Inflammation

• Neurogenesis

• Tissue remodelling

This may partly explain why some women with endometriosis also experience:

• Histamine intolerance

• Allergic tendencies

• Migraine

• Skin reactivity

Genetics and Epigenetics

Endometriosis is not purely genetic.

However, genetic susceptibility appears to influence risk.

Potential contributors include variations involving:

• Oestrogen receptor signalling

• HLA genes

• Detoxification pathways

• Oxidative stress pathways

• Angiogenesis pathways

• Immune regulation

Genes may load the gun, but environmental influences often pull the trigger.

Environmental Influences

Environmental toxicants are increasingly being investigated.

Particular attention has focused on:

• Dioxins

• Polychlorinated biphenyls (PCBs)

• Endocrine-disrupting chemicals

Research suggests these compounds may:

• Promote progesterone resistance

• Increase inflammatory signalling

• Increase MMP activity

• Enhance angiogenesis

• Alter immune regulation

Whilst exposure alone does not cause endometriosis, it may contribute to disease progression in susceptible individuals.

A Whole-System Approach

Endometriosis cannot be reduced to a simple hormone imbalance.

It involves interactions between:

• Hormones

• Immune function

• Nervous system regulation

• Pain processing

• Microbiome health

• Inflammation

• Oxidative stress

• Environmental exposures

Supporting women with endometriosis often requires a broad systems-based approach.

Areas worth exploring may include:

• Oestrogen metabolism and clearance

• Gut and vaginal microbiome health

• Histamine and mast cell activity

• Blood sugar regulation and insulin sensitivity

• Nervous system regulation

• Stress physiology

• Sleep quality

• Movement and pelvic physiotherapy

• Inflammatory load

• Environmental toxicant exposure

The Bigger Picture

Endometriosis is often described as a disease of misplaced tissue.

A more accurate description may be that it is a disorder of altered immune surveillance, chronic inflammation, abnormal pain processing, altered hormonal signalling and impaired tissue regulation.

The lesions are only part of the story.

The wider environment that allows those lesions to survive, grow and generate symptoms is where much of the ongoing research is now focused.

Understanding these interconnected systems provides a far richer picture of endometriosis and opens the door to a more personalised and comprehensive approach to supporting women living with the condition.