Polycystic ovary syndrome (PCOS) and endometriosis are two of the most common conditions affecting women’s reproductive health. While they share some overlapping symptoms, they are distinct in terms of causes, manifestations, and treatments. Misdiagnosis or confusion between the two can delay effective care, so understanding the differences is crucial.
Here, we look at the signs and symptoms of PCOS and endometriosis, and how both women and healthcare providers can distinguish between the two.
What is PCOS?
Polycystic ovary syndrome (PCOS) is a hormonal disorder that affects how the ovaries work. According to the NHS, it is one of the most common endocrine disorders, impacting approximately 1 in 10 women in the UK. The exact cause is unknown, but it’s associated with hormone imbalances, particularly excess androgens (male hormones) and insulin resistance.
Signs and symptoms of PCOS:
- Irregular periods: Periods may be infrequent, light, or absent.
- Excess hair growth (hirsutism): Particularly on the face, chest, and back, due to high androgen levels.
- Acne and oily skin: Often persistent and difficult to treat.
- Hair thinning: Pattern baldness or thinning hair on the scalp.
- Weight gain: Often difficult to manage, particularly around the abdomen.
- Polycystic ovaries: Visible on an ultrasound, but not always present.
- Infertility: Due to irregular ovulation or lack of ovulation.
The NHS also notes that many women with PCOS may not exhibit all these symptoms, and the severity can vary widely.
What is endometriosis?
Endometriosis occurs when tissue similar to the lining of the uterus (the endometrium) grows outside the uterus, commonly on the ovaries, fallopian tubes, and pelvic lining. This condition affects approximately 1 in 10 women of reproductive age in the UK, similar to PCOS. The misplaced tissue responds to hormonal changes during the menstrual cycle, leading to inflammation, scarring, and pain.
Key signs and symptoms of endometriosis:
- Pelvic pain: Particularly during periods (dysmenorrhea), but it can occur at any time.
- Pain during intercourse: Especially deep pain.
- Painful bowel movements or urination: Often during menstruation.
- Heavy or irregular periods: Including spotting between cycles.
- Fatigue: A common but often overlooked symptom.
- Infertility: Due to damage and scarring around reproductive organs.
- Bloating and nausea: Sometimes referred to as ‘endo belly.’
Unlike PCOS, endometriosis’s symptoms tend to be more focused on pain and inflammation, though the condition’s severity also varies from person to person.
How to differentiate between PCOS and endometriosis
Although PCOS and endometriosis can share symptoms like irregular periods and infertility, their underlying causes and hallmark symptoms differ significantly. Here’s how women and healthcare providers can tell them apart:
- Focus on pain:
- PCOS: Pain is not a primary symptom. While some women may experience discomfort, it is usually related to cysts rupturing or swelling rather than chronic pain.
- Endometriosis: Pain is a defining feature, often severe and persistent, especially during menstruation or certain activities like intercourse.
- Menstrual patterns:
- PCOS: Irregular or absent periods are common due to hormonal imbalances. Cycles may be sporadic or extremely long.
- Endometriosis: Periods tend to be heavy, prolonged, or accompanied by intense pain, rather than absent.
- Ultrasound findings:
- PCOS: Many women with PCOS have polycystic ovaries visible on ultrasound, but not all do. Polycystic ovaries contain multiple immature follicles that look like ‘cysts.’
- Endometriosis: While endometriosis doesn’t always show up on ultrasound, advanced cases may reveal endometriomas (chocolate cysts).
- Blood tests:
- PCOS: Hormonal blood tests often reveal high levels of androgens (e.g., testosterone) and sometimes insulin resistance.
- Endometriosis: There is no specific blood test to diagnose endometriosis, though some markers like CA-125 may be elevated in severe cases.
- Surgical diagnosis:
- PCOS: Rarely requires surgery for diagnosis.
- Endometriosis: Diagnosis often involves laparoscopy, a minimally invasive surgery to visualise and biopsy endometrial-like tissue.
Seeking help and diagnosis
Both conditions require thorough investigation and a tailored treatment plan. Here’s how you and your doctor can identify and manage each condition:
What women can do:
- Track symptoms: Use a menstrual and symptom diary to document pain, bleeding patterns, and other symptoms.
- Seek specialist care: Request referrals to endocrinologists (for PCOS) or gynaecologists (for endometriosis) if needed.
- Advocate for diagnostic tests: Push for ultrasounds, blood tests, or even laparoscopy if symptoms persist.
- Adopt a healthy lifestyle: Diet and exercise can help manage PCOS symptoms and reduce inflammation in endometriosis.
What doctors can do:
- Perform comprehensive assessments: Include detailed histories, physical exams, and targeted diagnostic tests.
- Avoid assumptions: Consider both PCOS and endometriosis when a woman presents with overlapping symptoms.
- Collaborate with specialists: Work with endocrinologists or fertility experts when needed.
- Provide pain management: Especially critical for endometriosis patients.
- In March 2025, it was reported that the first daily pill for treating endometriosis symptoms had been approved for use on the NHS in England (for patients who have tried all other options).
Improve the accuracy of diagnoses
PCOS and endometriosis are distinct conditions with significant impacts on women’s health. While PCOS is more focused on hormonal imbalances and irregular cycles, endometriosis is primarily characterised by chronic pain and inflammation. Recognising the differences can lead to quicker diagnosis and more effective treatments. If you suspect you have either condition, consult your GP and explore the resources available through the NHS.
