What Causes Endometriosis? How It Develops and What May Influence Its Growth

When you’re diagnosed with endometriosis, or you’re trying to understand years of unexplained symptoms, it’s natural to ask:

How did I get endometriosis?

You may wonder whether something you ate caused it, whether you waited too long to ask for help, or whether you could’ve done something differently.

The most important thing to know is that endometriosis isn’t your fault.

Researchers still don’t know exactly what causes endometriosis. There isn’t one habit, decision, or event that explains why one woman develops it and another doesn’t.

Instead, endometriosis appears to be a complex condition that may involve genetics, hormones, inflammation, immune system function, and the way certain cells develop or move through the body.

Understanding what researchers currently know can help you make sense of the condition without blaming yourself for something you didn’t cause.

What is endometriosis?

Endometriosis is a chronic inflammatory condition in which tissue similar to the lining inside the uterus grows in other areas of the body.

It’s most commonly found in the pelvis, including:

On or around the ovaries
On the fallopian tubes
Behind the uterus
Near the bladder or bowel
Along the lining of the pelvic cavity

This tissue isn’t exactly the same as the lining inside your uterus, but it can respond to hormonal changes. The surrounding tissue may become irritated and inflamed, and scar tissue called adhesions may form.

This can contribute to painful periods, chronic pelvic pain, pain during sex, bowel or bladder symptoms, and difficulty becoming pregnant.

However, endometriosis doesn’t affect everyone in the same way.

Some women have severe pain with a relatively small amount of visible disease. Others may have extensive endometriosis without experiencing obvious symptoms.

That’s why your pain level doesn’t always tell us how much endometriosis is present.

What causes endometriosis?

There’s currently no single proven cause of endometriosis.

Instead, researchers have developed several theories that may help explain how it begins. It’s possible that more than one of these processes contributes to the condition.

Retrograde menstruation

One of the most widely discussed theories is called retrograde menstruation.

Normally, menstrual blood leaves the uterus through the cervix and vagina. With retrograde menstruation, some menstrual fluid flows backward through the fallopian tubes and into the pelvic cavity.

Cells within that fluid may then attach to areas outside the uterus and begin growing.

However, retrograde menstruation can happen in women who never develop endometriosis. That means backward menstrual flow alone can’t fully explain the condition.

Other factors, such as genetics, inflammation, or the immune system’s response to those cells, may help determine whether the tissue survives and continues growing.

Genetics and family history

Endometriosis appears to have a genetic component.

Having a mother, sister, or daughter with endometriosis may increase your likelihood of developing it. However, that doesn’t mean you’ll definitely have endometriosis if it runs in your family.

It also doesn’t mean you can’t have it if no one in your family has been diagnosed.

Many women in previous generations lived with painful periods, pelvic pain, or infertility without ever receiving an accurate diagnosis. You may have a family history of symptoms even if no one used the word “endometriosis.”

Our article on whether endometriosis may be hereditary explains why learning more about your family’s health history can be helpful.

Immune system and inflammatory differences

Your immune system normally helps your body identify and clear cells that are growing where they shouldn’t.

Researchers are studying whether differences in immune system function allow endometriosis-related cells to survive, attach, and remain active outside the uterus. Emerging research has also found associations between endometriosis and immune system dysregulation.

Once lesions are present, they may contribute to ongoing inflammation in the surrounding area. That inflammation can irritate tissue, contribute to pain, and encourage the formation of scar tissue and adhesions.

This doesn’t mean endometriosis is simply an immune disorder. It means immune and inflammatory processes may be one part of a much larger picture.

Changes in cells or cell movement

Researchers have also considered whether certain cells can transform into endometriosis-like tissue.

Another theory suggests that endometriosis-related cells may travel through the bloodstream or lymphatic system.

These theories may help explain cases in which endometriosis is found in areas that can’t be fully explained by retrograde menstruation, including locations outside the pelvis.

No one theory explains every case, which is why researchers continue to study how different types of endometriosis may develop.

What causes endometriosis to grow?

When patients ask what causes endometriosis to grow, they may be wondering why lesions become larger, why symptoms feel worse, or whether the disease is spreading.

Several factors may influence how active endometriosis is.

Hormonal activity

Endometriosis tissue can respond to estrogen.

Estrogen doesn’t necessarily cause endometriosis on its own, but it may support the activity of tissue that’s already present. This is one reason some treatments for endometriosis focus on changing or suppressing hormonal activity.

However, hormonal treatment doesn’t work the same way for everyone. Endometriosis is more complex than having “too much estrogen,” and hormone levels are only one part of the picture.

Inflammation

Endometriosis can create an inflammatory environment in and around the pelvis.

That inflammation may contribute to irritation, pain, swelling, scar tissue, and adhesions. It may also help create an environment in which endometriosis lesions can continue to remain active.

Individual biology

Endometriosis doesn’t behave exactly the same way in every patient.

Different lesions may have different hormonal, inflammatory, or genetic characteristics. Two women can have endometriosis in similar locations but experience very different symptoms and responses to treatment.

That’s why endometriosis care shouldn’t be one-size-fits-all.

Does endometriosis always get worse over time?

Not necessarily.

Endometriosis may progress, remain relatively stable, or change in ways that are difficult to predict.

Symptoms can also become more intense without a major change in the visible amount of disease. Pain may be affected by inflammation, scar tissue, irritated nerves, pelvic floor tension, or another condition occurring alongside endometriosis.

Worsening pain doesn’t automatically mean the lesions have grown significantly.

The opposite can also be true. Some women have few symptoms but discover endometriosis during an evaluation for infertility.

You can learn more about the relationship between endometriosis and infertility.

Did you cause your endometriosis?

No evidence shows that you caused endometriosis by making the wrong personal choices.

Nutrition, movement, sleep, stress management, and other habits may affect how you feel or how you manage your symptoms. However, that isn’t the same as causing the condition.

You shouldn’t be blamed for developing endometriosis, and you shouldn’t be expected to fix a complex condition through willpower or lifestyle changes alone.

When should you talk to a specialist?

Painful periods may be common, but pain that regularly interrupts your life shouldn’t automatically be considered normal.

It may be time to ask for a closer evaluation if you experience:

Period pain that causes you to miss work, school, or normal activities
Pelvic pain before, during, or after your period
Pain during or after sex
Painful bowel movements or urination, especially around your period
Heavy or prolonged bleeding
Difficulty becoming pregnant
Pelvic pain that hasn’t improved with previous treatment
Symptoms that seem to be getting worse

Pelvic pain can have several possible causes. Our article on why you may experience cramps without a period explains why it’s important to look at the full pattern of your symptoms.

You didn’t cause your endometriosis

It’s natural to want a clear explanation for why endometriosis happened to you.

Right now, science can’t point to one single cause. What research does show is that endometriosis is a complex condition involving factors that are largely outside of your control.

You didn’t create it by doing something wrong.

You also don’t have to keep trying to understand your symptoms by yourself.

If painful periods, pelvic pain, or fertility concerns are affecting your life, it’s worth asking for a closer look. Depending on your symptoms and goals, your provider may discuss imaging, medication, fertility care, or whether surgery for endometriosis should be considered.

At The Kaldas Center, we’ll take the time to listen to your complete story, evaluate what may be contributing to your symptoms, and help you understand your options.

Schedule an appointment with The Kaldas Center to start getting answers.

Medical Disclaimer

This article is for educational purposes only and isn’t a substitute for medical advice, diagnosis, or treatment. If you have questions about pelvic pain, menstrual symptoms, fertility, or endometriosis, please speak with a qualified healthcare provider.