What Causes PCOS?
Understanding Why Polycystic Ovary Syndrome Develops
Introduction
One of the first questions many women ask after being diagnosed with Polycystic Ovary Syndrome (PCOS) is, "What caused it?"
It's an understandable question, but unfortunately there isn't a simple answer.
Unlike an infection or a broken bone, PCOS isn't caused by one single thing. Scientists believe it develops because of a combination of genetics, hormones, metabolism and environmental influences that begin long before symptoms appear.
For some women, PCOS runs strongly in families. Others have no obvious family history at all. Some are diagnosed during their teenage years because of irregular periods and acne, while others only discover they have PCOS after struggling to conceive.
Although researchers don't yet know the exact cause, they now understand far more about the biological changes that contribute to the condition than they did even twenty years ago.
Understanding these changes is important. It not only helps explain why PCOS develops, but also why treatments work differently for different women.
Quick Summary
There is no single cause of PCOS.
Genetics play an important role, but no single "PCOS gene" has been identified.
Hormonal imbalances begin long before symptoms become obvious.
Insulin resistance contributes to PCOS in many, but not all, women.
Inflammation, environmental factors and lifestyle may influence how PCOS develops.
PCOS is not caused by anything you did or didn't do.
There Isn't One Cause
One of the biggest misconceptions about PCOS is that it has a single cause.
In reality, PCOS is better thought of as a collection of biological changes that affect the body's hormone and metabolic systems.
Imagine building a tower using several blocks.
One block might represent genetics.
Another represents insulin.
Another represents hormones.
Another represents environmental influences.
For some women, several of these blocks are present. For others, only a few are involved. This is one reason why PCOS varies so much from person to person.
Researchers believe that PCOS develops when these different factors combine in a way that disrupts normal ovarian function.
Genetics: Does PCOS Run in Families?
The strongest evidence suggests that genetics play a major role.
If your mother, sister or daughter has PCOS, your own risk is significantly higher than someone without a family history.
Researchers have identified many genes that appear to increase the likelihood of developing PCOS, but none of them causes the condition on its own.
Instead, these genes appear to influence processes such as:
Hormone production
Insulin function
Egg development
Ovulation
Inflammation
Energy metabolism
Having these genes doesn't guarantee you'll develop PCOS. It simply means you may be more susceptible if other factors are also present.
This helps explain why PCOS often affects several generations within the same family but doesn't always look identical in each woman.
Hormonal Changes
Hormones are chemical messengers that allow different parts of the body to communicate.
In women with PCOS, this communication becomes disrupted.
One of the earliest changes appears to involve the relationship between the brain and the ovaries.
Normally, the brain carefully regulates the release of Follicle Stimulating Hormone (FSH) and Luteinising Hormone (LH). Together, these hormones guide the growth and release of an egg each month.
In many women with PCOS, LH levels are higher than expected compared with FSH.
This altered balance encourages the ovaries to produce more androgens, such as testosterone.
Higher androgen levels interfere with normal follicle development, making ovulation less likely and contributing to symptoms such as acne, excess hair growth and scalp hair thinning.
Importantly, not every woman with PCOS has the same hormone profile. This is another reason why symptoms vary so widely.
The Role of Insulin Resistance
One of the biggest breakthroughs in understanding PCOS has been recognising the importance of insulin.
Insulin is a hormone produced by the pancreas. Its main job is to help move glucose (sugar) from the bloodstream into the body's cells, where it can be used for energy.
In many women with PCOS, the body's cells become less responsive to insulin. This is known as insulin resistance.
To compensate, the pancreas produces more insulin.
High insulin levels affect far more than blood sugar.
They also stimulate the ovaries to produce additional androgens.
Those higher androgen levels make ovulation more difficult, increasing many of the symptoms associated with PCOS.
This creates a cycle:
Insulin resistance leads to higher insulin levels.
Higher insulin levels increase androgen production.
Higher androgen levels interfere with ovulation.
Irregular ovulation contributes to further hormonal imbalance.
However, insulin resistance is not present in every woman with PCOS. Women with lean PCOS, for example, may have little or no insulin resistance, showing that other biological pathways can also lead to the condition.
Inflammation
Researchers have also found evidence that many women with PCOS have low-grade chronic inflammation.
Unlike the inflammation that occurs when you cut your finger or develop an infection, this type of inflammation is subtle and long-lasting.
Scientists are still investigating whether inflammation causes PCOS or develops as a result of it.
Either way, inflammatory chemicals appear capable of increasing androgen production and worsening insulin resistance, adding another layer to the condition.
This is an active area of research, and there is still much to learn.
Could PCOS Begin Before Birth?
One of the most fascinating areas of current research suggests that the foundations of PCOS may begin before a girl is even born.
Some scientists believe that exposure to higher levels of androgens during fetal development may influence how the ovaries, brain and metabolism develop.
This theory could help explain why PCOS often appears early in life and why it tends to run in families.
At present, this remains a theory rather than an established fact, and researchers continue to investigate its role.
The Gut Microbiome
Another exciting area of research focuses on the trillions of bacteria that live in the digestive system, collectively known as the gut microbiome.
The gut microbiome plays an important role in digestion, immunity and metabolism.
Some studies have found differences in the gut bacteria of women with PCOS compared with women without the condition.
Researchers are exploring whether these differences contribute to inflammation, insulin resistance or hormone regulation.
Although this field shows promise, we still don't know whether changes in the microbiome are a cause of PCOS, a consequence of it, or both.
Does Weight Cause PCOS?
No.
This is one of the most damaging myths surrounding the condition.
Many women are told, either directly or indirectly, that their weight caused their PCOS.
Current evidence does not support this.
Women of every body size can develop PCOS.
Weight can influence the severity of symptoms in some women because excess body fat may worsen insulin resistance and hormone imbalance.
However, it does not cause the underlying condition.
Lean women develop PCOS.
Teenagers develop PCOS before significant weight changes occur.
Women who have always maintained a healthy weight can still experience irregular periods, infertility and high androgen levels.
Weight is one factor that may affect how PCOS presents, but it is not the root cause.
Did I Cause My PCOS?
Many women wonder whether something they did caused the condition.
Did they eat the wrong foods?
Exercise too little?
Take the wrong medication?
Become overweight?
The answer is almost certainly no.
PCOS develops through a complex interaction between genetics, hormones and metabolism—factors that are largely outside your control.
While healthy lifestyle habits can improve symptoms for many women, they cannot erase the biological changes that led to PCOS developing in the first place.
You did not cause your PCOS, and you should not blame yourself for having it.
Why Researchers Still Don't Have All the Answers
Although our understanding of PCOS has improved dramatically, there is still much we don't know.
Scientists continue to study:
Why some women ovulate normally despite having PCOS.
Why symptoms differ so much.
Why some women have insulin resistance while others do not.
The role of genetics and epigenetics.
The influence of the gut microbiome.
New treatments that target the underlying biology rather than simply managing symptoms.
Each year brings new discoveries, offering hope for more personalised approaches to diagnosis and treatment in the future.
Key Takeaways
PCOS does not have a single cause.
Genetics, hormones, insulin resistance and environmental influences all appear to contribute.
Different factors affect different women, explaining why symptoms vary so widely.
Weight does not cause PCOS, although it can influence symptom severity in some women.
Researchers continue to learn more about PCOS, and our understanding of the condition is improving all the time.
Frequently Asked Questions
Can stress cause PCOS?
Stress does not cause PCOS, but chronic stress can affect hormone levels and menstrual cycles, potentially making symptoms feel worse.
Can you prevent PCOS?
There is currently no known way to prevent PCOS because much of the risk is linked to genetics and biology. However, healthy lifestyle habits can help reduce the impact of symptoms and lower the risk of some long-term complications.
Why do two women with PCOS have completely different symptoms?
PCOS is a spectrum. Different combinations of hormone imbalance, insulin resistance, genetics and other factors mean that no two women experience the condition in exactly the same way.
References
This article should reference high-quality sources such as:
International Evidence-based Guideline for the Assessment and Management of PCOS
European Society of Human Reproduction and Embryology (ESHRE)
American Society for Reproductive Medicine (ASRM)
National Institute for Health and Care Excellence (NICE)
Peer-reviewed research on genetics, insulin resistance and PCOS.