What Is the Reason for Having PCOD? The Science Behind One of the World’s Most Common Hormonal Disorders (2026)

Introduction: Understanding a Complex Hormonal Disorder

A teenage girl experiences irregular menstrual cycles for years. A young woman struggles with infertility despite having no immediately identifiable cause. Another develops insulin resistance and prediabetes in her twenties. Although these situations may appear unrelated, they can share a common underlying cause: Polycystic Ovary Syndrome (PCOS), a condition commonly referred to as Polycystic Ovarian Disease (PCOD) in some regions, particularly in South Asia.

Polycystic Ovary Syndrome (PCOS) is one of the most common endocrine disorders affecting women of reproductive age. Depending on the diagnostic criteria applied, PCOS affects approximately 8–13% of women worldwide, with prevalence estimates exceeding 20% in some populations. Far from being merely an ovarian disorder, PCOS influences reproductive health, metabolism, cardiovascular risk factors, and psychological well-being.

Among the most common questions asked by patients, families, and students is:

“What is the reason for having PCOD?”

The scientific answer is that there is no single cause. Instead, PCOS develops through a complex interaction among genetic susceptibility, hormonal imbalance, insulin resistance, ovarian dysfunction, chronic low-grade inflammation, neuroendocrine dysregulation, and environmental influences.

Understanding why PCOS occurs provides valuable insight into how the reproductive, endocrine, and metabolic systems function as an interconnected biological network.

PCOD vs PCOS: Understanding the Terminology

Although PCOD (Polycystic Ovarian Disease) and PCOS (Polycystic Ovary Syndrome) are frequently used interchangeably in public discussions, PCOS is the internationally accepted medical term used in modern scientific literature and clinical guidelines.

In many countries, particularly in South Asia, the term PCOD (Polycystic Ovarian Disease) remains widely used in public discussions and healthcare settings. However, PCOD is not a formally recognized diagnostic category in contemporary international clinical guidelines. The internationally accepted medical term is Polycystic Ovary Syndrome (PCOS).

Because PCOD is commonly used by patients and the general public, both terms may appear in this article. Unless otherwise specified, references to PCOD are intended to refer to PCOS.

Quick Answer: What Causes PCOD?

There is no single cause of PCOD.

Current scientific evidence shows that the condition develops through a complex interaction among:

• Genetic susceptibility
• Insulin resistance
• Excess androgen production
• Abnormal ovarian follicle development
• Neuroendocrine dysfunction
• Chronic low-grade inflammation
• Environmental and lifestyle influences

Rather than resulting from one trigger, PCOD develops when multiple biological mechanisms interact over time.

Scientific Background

What Is PCOS?

PCOS is a hormonal and metabolic disorder characterized by a combination of:

• Irregular or absent ovulation
• Elevated androgen (male-type hormone) levels
• Multiple immature ovarian follicles
• Metabolic abnormalities such as insulin resistance

Despite the term “polycystic,” the structures seen on ultrasound are usually not true cysts. Instead, they are immature follicles that fail to complete normal development and ovulation.

Today, scientists recognize PCOS as a systemic endocrine-metabolic disorder rather than a disease confined to the ovaries.

Historical Development

The condition was first described in 1935 by physicians Irving Stein and Michael Leventhal, who observed a combination of enlarged ovaries, infertility, menstrual irregularities, and excessive hair growth.

For decades, PCOS was viewed primarily as a reproductive disorder. Research conducted during the late twentieth century revealed strong links between PCOS, insulin resistance, obesity, and type 2 diabetes. These discoveries fundamentally transformed scientific understanding of the condition.

Today, PCOS is recognized as a disorder involving the reproductive, endocrine, and metabolic systems simultaneously.

Why PCOS Is Difficult to Diagnose

One reason PCOS remains a challenging condition is that there is no single laboratory test, imaging study, or genetic marker that can definitively confirm or exclude the diagnosis.

Instead, PCOS is considered a clinical syndrome, meaning that diagnosis relies on a combination of:

• Symptoms
• Hormonal findings
• Menstrual patterns
• Ovarian characteristics

This helps explain why different diagnostic criteria may identify somewhat different groups of patients and why prevalence estimates vary across studies.

Scientific Confidence: High

PCOS Phenotypes: Why Symptoms Vary Between Individuals

One reason PCOS presents differently among individuals is that the syndrome encompasses several recognized phenotypes.

Under the Rotterdam criteria, four major phenotypes are commonly described:

Research suggests that metabolic risk, reproductive complications, and symptom severity may differ among these phenotypes.

This variability helps explain why two women diagnosed with PCOS may experience substantially different symptoms and long-term health outcomes.

Scientific Confidence: High

How Common Is PCOS?

The prevalence of PCOS varies because different medical organizations use different diagnostic criteria.

Polycystic Ovary Syndrome (PCOS) is considered one of the leading causes of ovulatory infertility worldwide.

Why Do Prevalence Estimates Vary?

Because these frameworks identify somewhat different patient populations, prevalence estimates can vary substantially between studies.

Ethnic and Population Differences

Research has shown that PCOS does not present identically across all populations.

Differences have been observed in:

• Insulin resistance
• Metabolic complications
• Androgen-related symptoms
• Body composition
• Cardiovascular risk factors

For example, some Asian populations may develop metabolic complications at lower body mass indices than Western populations, while symptom patterns may differ among Middle Eastern, European, African, and Latin American populations.

These observations suggest that genetic, environmental, cultural, and lifestyle factors all contribute to how PCOS manifests in different individuals.

Scientific Confidence: Moderate to High

What Is the Reason for Having PCOD?

Current scientific evidence indicates that PCOS develops through interactions among several biological processes, including:

• Genetic predisposition
• Insulin resistance
• Excess androgen production
• Abnormal ovarian follicle development
• Neuroendocrine dysfunction
• Chronic inflammation
• Environmental and lifestyle influences

Rather than being caused by a single factor, PCOS emerges when multiple biological mechanisms interact over time.

The Biological Mechanisms Behind PCOS

1. Genetic Susceptibility: The Biological Foundation

Family history is one of the strongest risk factors for PCOS.

Women with an affected mother or sister are significantly more likely to develop the condition. Twin and family studies consistently demonstrate a substantial hereditary component.

What Have Scientists Discovered?

Large genome-wide association studies (GWAS) have identified numerous genetic regions associated with PCOS risk.

Many of these genetic variants are associated with biological pathways involved in:

• Insulin signaling
• Ovarian steroid hormone production
• Follicular development
• Energy metabolism
• Neuroendocrine regulation

Rather than being caused by a single genetic mutation, PCOS appears to result from the combined effects of multiple genetic variants that collectively increase susceptibility.

This pattern is typical of many complex chronic diseases.

Scientific Confidence: High

2. Insulin Resistance: A Central Driver

Among the biological mechanisms associated with PCOS, insulin resistance is considered one of the most important contributors in many patients. However, PCOS is a heterogeneous disorder, and the relative importance of insulin resistance varies among individuals. Some women exhibit pronounced metabolic dysfunction, whereas others display predominantly reproductive or androgen-related abnormalities with comparatively little evidence of insulin resistance.

Understanding Insulin Resistance

Insulin is a hormone produced by the pancreas that helps cells absorb glucose from the bloodstream.

When cells become less responsive to insulin:

1. Blood glucose begins to rise.
2. The pancreas produces additional insulin.
3. Hyperinsulinemia (high insulin levels) develops.

Approximately 50–75% of women with PCOS exhibit measurable insulin resistance, although prevalence varies according to body weight, ethnicity, age, and diagnostic criteria.

Importantly, insulin resistance is common but not universal. Some women—particularly those with lean PCOS—may demonstrate normal insulin sensitivity on standard clinical testing while still meeting diagnostic criteria.

Why Excess Insulin Matters

Excess insulin:

• Stimulates ovarian androgen production
• Reduces sex hormone-binding globulin (SHBG)
• Increases circulating testosterone
• Worsens metabolic dysfunction

Researchers increasingly describe a self-reinforcing cycle:

Insulin Resistance → Elevated Insulin → Increased Androgens → Worsened Insulin Resistance

Scientific Confidence: High

Lean PCOS: Why Body Weight Is Not the Whole Story

A common misconception is that PCOS occurs only in individuals who are overweight or obese.

In reality, a substantial proportion of women with PCOS have body weights within the normal range. This form is often referred to as lean PCOS.

Women with lean PCOS may still experience:

• Irregular menstrual cycles
• Ovulatory dysfunction
• Elevated androgen levels
• Acne
• Infertility

Although obesity can worsen symptoms and metabolic risk, excess body weight is not required for PCOS to develop.

Scientific Confidence: High

3. Hyperandrogenism: The Hormonal Signature

Hyperandrogenism refers to elevated levels of male-type hormones such as testosterone.

Approximately 50–80% of women with PCOS exhibit clinical or biochemical evidence of androgen excess.

The Role of Ovarian Theca Cells

In PCOS:

• Theca cells become overactive.
• Androgen production increases.
• Follicular maturation becomes impaired.

Clinical Manifestations

Scientific Confidence: High

4. Adrenal Androgen Production: An Additional Source of Hormonal Excess

Although the ovaries are the primary source of excess androgen production in many women with PCOS, the adrenal glands may also contribute.

Some women with PCOS exhibit elevated levels of adrenal androgens, particularly dehydroepiandrosterone sulfate (DHEAS).

The reasons for increased adrenal androgen production are not fully understood but may involve altered adrenal responsiveness to hormonal signals and genetic susceptibility.

These findings suggest that androgen excess in PCOS can arise from multiple biological sources rather than the ovaries alone.

Scientific Confidence: Moderate to High

5. Follicular Arrest: Why Ovulation Fails

Under normal circumstances, one ovarian follicle becomes dominant and releases a mature egg during ovulation.

In PCOS, multiple follicles begin development but stall before maturation.

The result is:

• Infrequent ovulation
• Absent ovulation
• Accumulation of immature follicles

This process explains the characteristic ovarian appearance observed on ultrasound.

Scientific Confidence: High

6. Anti-Müllerian Hormone (AMH): An Important Emerging Player

Women with PCOS frequently exhibit substantially elevated Anti-Müllerian Hormone (AMH) concentrations, often two to four times higher than those observed in women without the condition.

Because AMH is produced by developing ovarian follicles, elevated levels likely reflect the increased number of immature follicles characteristic of PCOS.

Research suggests elevated AMH may:

• Interfere with follicular maturation
• Alter hormonal signaling pathways
• Contribute to ovulatory dysfunction

Scientists are investigating whether AMH is simply a marker of ovarian dysfunction or an active contributor to disease development.

Scientific Confidence: Moderate to High

Although AMH has attracted considerable attention as a potential biomarker for PCOS, current international guidelines do not recommend using AMH as a standalone diagnostic test. Instead, AMH should be interpreted in conjunction with clinical findings, hormonal assessments, and imaging studies when appropriate.

7. The Brain-Ovary Connection

The reproductive system depends on communication among:

• The hypothalamus
• The pituitary gland
• The ovaries

Together, these structures form the Hypothalamic-Pituitary-Ovarian (HPO) Axis.

Many women with PCOS exhibit:

• Elevated luteinizing hormone (LH)
• Relatively lower follicle-stimulating hormone (FSH)

This imbalance promotes androgen production while impairing normal follicular development.

Scientific Confidence: High

8. Chronic Inflammation and Adipose Tissue Dysfunction

Researchers increasingly recognize PCOS as a condition involving chronic low-grade inflammation.

Women with PCOS often exhibit elevated levels of:

• C-reactive protein (CRP)
• Interleukin-6
• Tumor necrosis factor-alpha (TNF-α)

Fat Tissue as an Endocrine Organ

Adipose tissue actively produces signaling molecules that influence:

• Insulin sensitivity
• Hormone metabolism
• Inflammation

This helps explain why obesity can worsen symptoms even though it is not the primary cause of PCOS.

Scientific Confidence: Moderate to High

Although elevated inflammatory markers are consistently observed in many women with PCOS, researchers continue to debate whether inflammation is a primary driver of disease development, a consequence of metabolic abnormalities, or both.

Visual Summary: How PCOS Develops

Genetic Susceptibility
+
Environmental and Developmental Influences
↓
Metabolic, Hormonal, and Neuroendocrine Dysregulation
(Insulin Resistance, Hyperinsulinemia,
Hyperandrogenism and HPO-Axis Dysfunction)
↓
Impaired Follicular Development (Follicular Arrest)
↓
Ovulatory Dysfunction (Oligo-/Anovulation)
↓
Reproductive, Androgenic, and Metabolic Manifestations of PCOS

Although simplified, this model illustrates how reproductive and metabolic abnormalities can reinforce one another over time.

What Scientists Know with High Confidence

Current scientific evidence strongly supports the following conclusions:

• Genetic susceptibility contributes significantly to disease risk.
• Hyperandrogenism is a central biological feature.
• Insulin resistance plays an important role in many patients.
• Follicular maturation is disrupted.
• PCOS affects both metabolic health and reproductive function.
• PCOS is a systemic endocrine-metabolic disorder rather than a disease of the ovaries alone.

Current Research and Recent Discoveries

Prenatal Androgen Exposure and Developmental Origins

One influential hypothesis proposes that susceptibility to PCOS may begin before birth.

Animal studies and human observational research suggest that exposure to elevated androgen levels during fetal development may alter the maturation of reproductive, metabolic, and neuroendocrine systems.

Researchers are investigating whether prenatal hormonal environments may increase the likelihood of developing PCOS later in life.

Although evidence supporting this developmental-origin theory continues to grow, important questions remain regarding its relevance to different PCOS phenotypes.

Scientific Confidence: Moderate

The Gut Microbiome Hypothesis

Researchers have identified consistent differences in gut microbial populations between women with and without PCOS.

Potential mechanisms include:

• Altered metabolism
• Increased inflammation
• Hormonal regulation
• Changes in insulin sensitivity

Scientific Confidence: Moderate

Scientists have not yet established whether microbiome changes are causes, consequences, or both.

Epigenetics and Early-Life Programming

Researchers are investigating whether:

• Maternal obesity
• Maternal diabetes
• Prenatal androgen exposure

may increase future susceptibility to PCOS through epigenetic mechanisms.

Scientific Confidence: Moderate

This remains an active and rapidly evolving area of research.

Precision Medicine and Modern Guidelines

Recent international guidelines emphasize increasingly individualized approaches to diagnosis and management.

Future therapies may be tailored according to:

• Genetic profiles
• Metabolic characteristics
• Hormonal patterns
• Reproductive goals

This individualized approach represents a major evolution in PCOS care.

Real-World Clinical Example

Consider a 24-year-old woman who presents with irregular menstrual cycles and persistent acne despite maintaining a normal body weight. Laboratory evaluation reveals elevated testosterone and insulin levels, while ultrasound examination demonstrates multiple small immature follicles within the ovaries.

This case highlights an important clinical reality: PCOS can occur in individuals who do not fit the commonly held stereotypes associated with the condition. Rather than being defined by body weight alone, PCOS is a complex endocrine-metabolic disorder characterized by interacting hormonal, reproductive, and metabolic abnormalities.

Real-World Health Impact

PCOS affects far more than fertility. Long-term studies indicate that women with PCOS have a substantially increased risk of developing type 2 diabetes, with many studies reporting approximately a two- to fourfold higher risk compared with women without the condition.

Additional health concerns associated with PCOS include:

These associations underscore the importance of long-term monitoring, preventive care, and management of both reproductive and metabolic health.

PCOS Across the Lifespan

PCOS is not solely a condition of reproductive-age women. Its manifestations may evolve throughout life.

During adolescence, irregular menstrual cycles and acne are common presenting features.

During reproductive years, infertility, ovulatory dysfunction, and metabolic abnormalities often become more prominent.

Later in life, concerns increasingly shift toward cardiovascular risk factors, type 2 diabetes, and long-term metabolic health.

This lifespan perspective highlights the importance of ongoing monitoring and individualized care beyond fertility-related concerns.

Scientific Confidence: High

Why PCOS Is Considered a Systemic Disorder

Historically, PCOS was viewed primarily as a disease of the ovaries.

Modern research has fundamentally changed this perspective.

Scientists now recognize that PCOS can affect:

• Reproductive function
• Glucose metabolism
• Insulin sensitivity
• Cardiovascular risk factors
• Inflammatory pathways
• Mental health and quality of life

For this reason, PCOS is increasingly described as a systemic endocrine-metabolic disorder rather than a condition confined to the reproductive system.

This broader understanding has important implications for long-term monitoring, prevention, and treatment strategies.

What Scientists Still Do Not Know

Despite decades of research, several important questions remain unanswered:

• Why do symptoms vary dramatically between individuals?
• Why do some genetically susceptible women never develop clinically significant disease?
• Are microbiome changes a cause of PCOS or a consequence?
• Does elevated AMH actively drive disease progression?
• Which biological mechanisms are most important in different patients?

Some researchers increasingly propose that PCOS may represent a collection of related biological subtypes rather than a single disorder.

Under this model, different individuals may develop similar symptoms via partially distinct biological pathways.

Determining whether PCOS represents one condition or several closely related conditions remains one of the most important questions in contemporary research.

Modern International Guideline

The most widely cited contemporary recommendations are provided by the 2023 International Evidence-Based Guideline for the Assessment and Management of Polycystic Ovary Syndrome.

These guidelines emphasize:

• Evidence-based diagnosis
• Individualized treatment approaches
• Screening for metabolic complications
• Mental health assessment
• Lifestyle interventions as foundational therapy
• Shared decision-making between patients and healthcare professionals

The guideline reflects the growing recognition that PCOS is a complex endocrine-metabolic disorder requiring comprehensive long-term management.

Can PCOS Be Prevented?

Because genetic susceptibility plays an important role, there is currently no guaranteed way to prevent PCOS entirely.

However, healthy lifestyle habits may reduce symptom severity, improve metabolic health, and lower the risk of long-term complications.

Recommended strategies include:

• Regular physical activity
• Balanced nutrition
• Weight management when appropriate
• Adequate sleep
• Stress management
• Early screening in high-risk individuals

Although these measures may not prevent PCOS entirely, they can improve long-term health outcomes.

Key Takeaways

• There is no single reason for having PCOD.
• Genetics, insulin resistance, hormones, and environmental influences all contribute.
• Insulin resistance is one of the most important biological drivers.
• Hyperandrogenism disrupts ovulation and causes many hallmark symptoms.
• PCOS affects both reproductive and metabolic health.
• Lean individuals can also develop PCOS.
• Emerging research is exploring roles for the gut microbiome and epigenetics.
• Future treatments are likely to become increasingly personalized.

Frequently Asked Questions

What is the primary cause of PCOD?

There is no single known cause of PCOS. Current evidence suggests that the condition arises from complex interactions among genetic susceptibility, metabolic dysfunction (including insulin resistance in many individuals), hormonal and neuroendocrine abnormalities, inflammatory processes, and environmental influences. The relative contribution of these factors varies between individuals.

Can thin women develop PCOD?

Yes. PCOS can occur in women of any body weight. Although obesity may worsen symptoms and increase metabolic risk, many women with normal body weight develop PCOS and may experience reproductive, hormonal, and metabolic manifestations of the condition.

Is PCOD inherited?

Yes. Family history significantly increases the risk of PCOS, indicating a strong genetic component. However, PCOS is a complex polygenic disorder influenced by interactions among genetic, environmental, and developmental factors.

Why are periods irregular in PCOD?

Hormonal imbalances in PCOS can disrupt normal follicular development and ovulation. As a result, ovulation may occur infrequently or not at all, leading to irregular, infrequent, or absent menstrual periods.

Does PCOD always cause infertility?

No. PCOS does not always cause infertility. Many women with PCOS conceive naturally. However, ovulatory dysfunction can reduce fertility and make conception more challenging for some individuals.

Can PCOD increase diabetes risk?

Yes. Many individuals with Polycystic Ovary Syndrome (PCOS) have insulin resistance, which increases the risk of developing prediabetes and type 2 diabetes. Long-term studies consistently show that people with PCOS face a higher risk of glucose metabolism disorders than those without the condition.

Is there a cure?

There is currently no cure for PCOS. However, symptoms and long-term health risks can often be effectively managed through lifestyle measures, medical treatment, and individualized care.

Conclusion

The question “What is the reason for having PCOD?” does not have a simple answer.

Modern scientific evidence indicates that PCOS develops through a complex interaction among genetic susceptibility, insulin resistance, androgen excess, abnormal follicular development, neuroendocrine dysfunction, inflammation, and environmental influences.

Among these factors, insulin resistance, hyperandrogenism, disrupted follicular maturation, and dysfunction of the hypothalamic-pituitary-ovarian axis have the strongest scientific evidence.

At the same time, emerging research into the gut microbiome, epigenetics, and disease subtypes is reshaping our understanding of why PCOS develops and why its manifestations differ among individuals.

Perhaps the most important scientific lesson from PCOS is that reproductive, endocrine, and metabolic systems do not function independently. Instead, they operate as deeply interconnected biological networks.

Understanding the causes of PCOS, therefore, provides insight not only into one of the world’s most common hormonal disorders but also into the broader biology of complex chronic disease.

Future advances in precision medicine may allow clinicians to tailor prevention and treatment strategies according to each individual’s unique genetic, metabolic, and hormonal profile.

While many aspects of PCOS biology are now well established, ongoing research continues to refine our understanding of the condition, making PCOS one of the most actively studied disorders in reproductive endocrinology.

References

1. Teede HJ, Tay CT, Laven JJE, et al. Recommendations From the 2023 International Evidence-Based Guideline for the Assessment and Management of Polycystic Ovary Syndrome. Journal of Clinical Endocrinology & Metabolism. 2023;108(10):2447–2489. Available at: https://pubmed.ncbi.nlm.nih.gov/37580861/
2. Rotterdam ESHRE/ASRM-Sponsored PCOS Consensus Workshop Group. Revised 2003 Consensus on Diagnostic Criteria and Long-Term Health Risks Related to Polycystic Ovary Syndrome (PCOS). Human Reproduction. 2004;19(1):41–47. Available at: https://pubmed.ncbi.nlm.nih.gov/14688154/
3. Legro RS, Arslanian SA, Ehrmann DA, et al. Diagnosis and Treatment of Polycystic Ovary Syndrome: An Endocrine Society Clinical Practice Guideline. Journal of Clinical Endocrinology & Metabolism. 2013;98(12):4565–4592. Available at: https://doi.org/10.1210/jc.2013-2350
4. Goodarzi MO, Dumesic DA, Chazenbalk G, Azziz R. Polycystic Ovary Syndrome: Etiology, Pathogenesis and Diagnosis. Nature Reviews Endocrinology. 2011;7(4):219–231. Available at: https://doi.org/10.1038/nrendo.2010.217
5. Escobar-Morreale HF. Polycystic Ovary Syndrome: Definition, Aetiology, Diagnosis and Treatment. Nature Reviews Endocrinology. 2018;14(5):270–284. Available at: https://doi.org/10.1038/nrendo.2018.24
6. Teede HJ, Misso ML, Costello MF, et al. International Evidence-Based Guideline for the Assessment and Management of Polycystic Ovary Syndrome. Melbourne: Monash University; 2023. Available at: https://www.monash.edu/medicine/mchri/pcos/guideline
7. Azziz R, Carmina E, Dewailly D, et al. The Androgen Excess and PCOS Society Criteria for PCOS. Available at: The Androgen Excess and PCOS Society criteria for the polycystic ovary syndrome: the complete task force report – PubMed

Disclaimer

This article is intended for educational and informational purposes only. It summarizes current scientific knowledge and clinical understanding of Polycystic Ovary Syndrome (PCOS), also commonly referred to as PCOD in some regions.

Although the information presented is based on peer-reviewed research, clinical guidelines, and published scientific literature, it should not be considered a substitute for professional medical advice, diagnosis, or treatment. PCOS is a complex and highly individualized condition, and symptoms, health risks, and treatment responses may vary substantially between individuals.

Scientific understanding of PCOS continues to evolve. Areas such as genetics, epigenetics, the gut microbiome, disease subtypes, and long-term health outcomes remain active fields of research, and future discoveries may refine current knowledge.

Individuals experiencing symptoms or health concerns related to PCOS should consult a qualified healthcare professional for personalized evaluation and medical guidance. Clinical decisions should always be based on individual medical assessment rather than general educational information.

While every effort has been made to ensure accuracy at the time of publication, the authors and publishers make no guarantee that all information will remain current as scientific evidence continues to develop.

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