PCOS and endometriosis are two distinct conditions that affect the reproductive system in fundamentally different ways. PCOS is a hormonal and metabolic disorder that disrupts ovulation, while endometriosis is a condition where tissue similar to the uterine lining grows in places it shouldn’t, causing inflammation and pain. Both can cause pelvic pain and fertility problems, which is why they’re often confused, but their causes, symptoms, and treatments have little in common.
What Drives Each Condition
PCOS is rooted in a hormone imbalance. The ovaries produce too many androgens (often called “male hormones,” though all women produce them in small amounts). These elevated androgen levels interfere with the normal development and release of eggs. Instead of one mature egg being released each cycle, an excess number of small, immature eggs accumulate under the surface of the ovary. This is where the “polycystic” name comes from: the ovaries can appear studded with many small follicles on an ultrasound. PCOS also commonly involves insulin resistance, meaning the body struggles to use insulin efficiently, which in turn can drive androgen levels even higher.
Endometriosis works through a completely different mechanism. Tissue that resembles the lining of the uterus (the endometrium) grows outside the uterus, attaching to surfaces like the ovaries, fallopian tubes, bladder, or bowel. This displaced tissue responds to hormonal cycles just like the uterine lining does: it thickens, breaks down, and bleeds with each period. But because there’s no way for the blood to leave the body, it causes chronic inflammation, swelling, and scar tissue. The condition is estrogen-dependent, meaning estrogen fuels its growth, which is essentially the opposite hormonal picture from PCOS.
How the Symptoms Differ
The hallmark of endometriosis is pain, particularly severe menstrual cramps that go well beyond normal period discomfort. This pain often starts before your period and can last for days. Many people with endometriosis also experience pain during sex, painful bowel movements or urination (especially around menstruation), chronic pelvic pain between periods, and fatigue. The severity of pain doesn’t always match the extent of the disease: someone with a small amount of displaced tissue can have debilitating symptoms, while someone with widespread endometriosis may have relatively little pain.
PCOS presents very differently. The most common signs are irregular or absent periods, because ovulation isn’t happening on a predictable schedule. Excess androgens cause visible effects: acne (particularly along the jawline, chin, and upper back), thinning hair on the scalp, and excess hair growth on the face, chest, or abdomen. Weight gain, especially around the midsection, is common due to the underlying insulin resistance. Some people with PCOS also develop darkened patches of skin in body folds like the neck, armpits, or groin.
The overlap between the two conditions is limited but real. Both can cause pelvic pain and both can make it harder to get pregnant. This is usually where the similarities end. If your primary symptom is severe period pain with relatively regular cycles, endometriosis is the more likely culprit. If your cycles are unpredictable and you’re noticing hormonal skin or hair changes, PCOS is more probable.
Prevalence and Diagnosis
PCOS affects an estimated 10 to 13% of women of reproductive age, making it one of the most common hormonal disorders. The WHO estimates that up to 70% of women with PCOS worldwide remain undiagnosed. Endometriosis affects roughly 10% of reproductive-age women, and it too is widely underdiagnosed, with an average delay of 7 to 10 years from symptom onset to diagnosis.
The diagnostic process for each condition is quite different. PCOS is diagnosed based on a combination of clinical signs: irregular periods, evidence of excess androgens (either through blood tests or visible symptoms like acne and excess hair growth), and sometimes an ultrasound showing enlarged ovaries with many small follicles. An ovarian volume of 10 ml or greater, or 10 or more follicles visible per ovary section, supports the diagnosis. A blood test measuring anti-Müllerian hormone (AMH) can also be used as an alternative to ultrasound. Notably, if someone already has irregular cycles and clear signs of excess androgens, neither an ultrasound nor an AMH test is required to make the diagnosis.
Endometriosis is harder to confirm. Imaging like ultrasound or MRI can sometimes detect larger deposits of displaced tissue or cysts on the ovaries (called endometriomas), but smaller or more superficial growths often don’t show up. The gold standard for definitive diagnosis has traditionally been laparoscopy, a minimally invasive surgery where a camera is inserted through a small abdominal incision to directly visualize and biopsy the tissue. Many clinicians now treat based on symptoms and imaging without requiring surgery, but the difficulty of diagnosis is a major reason endometriosis goes unrecognized for so long.
How Each Condition Affects Fertility
Both conditions are leading causes of difficulty getting pregnant, but they interfere with conception through entirely different pathways.
With PCOS, the problem is ovulation. High androgen levels prevent eggs from maturing and being released. If you’re not ovulating, there’s no egg available to be fertilized. The good news is that this is one of the more treatable causes of infertility. Medications that stimulate ovulation are often effective, and lifestyle changes that improve insulin sensitivity (like regular exercise and dietary adjustments) can sometimes restore ovulation on their own. PCOS is one of the most common causes of irregular menstrual cycles and infertility, but many people with PCOS do conceive with appropriate support.
Endometriosis affects fertility in more structural ways. Scar tissue and adhesions can physically distort the pelvic anatomy, blocking or damaging the fallopian tubes. Inflammation in the pelvic cavity can also create a hostile environment for eggs, sperm, and embryos. Endometriomas on the ovaries can damage healthy ovarian tissue and reduce egg supply over time. Even mild endometriosis without obvious structural damage appears to reduce fertility, possibly through inflammatory chemicals that interfere with fertilization or implantation. Treatment may involve surgery to remove endometriosis deposits and scar tissue, or proceeding directly to IVF, which bypasses many of the physical barriers the condition creates.
Long-Term Health Risks
PCOS carries significant metabolic consequences beyond the reproductive system. Insulin resistance, present in the majority of people with PCOS regardless of body weight, increases the risk of developing type 2 diabetes. The risk of gestational diabetes during pregnancy is also elevated. Cardiovascular risk factors like high cholesterol, high blood pressure, and elevated blood sugar tend to cluster together in PCOS. Because irregular or absent periods mean the uterine lining isn’t being shed regularly, the lining can build up over time, which raises the risk of endometrial thickening and, in some cases, endometrial cancer. Depression and anxiety are also more common in people with PCOS, likely driven by a combination of hormonal effects and the psychological burden of visible symptoms.
Endometriosis carries its own set of long-term concerns. Chronic pain can become progressively harder to manage and may persist even after menopause in some cases. Repeated surgeries can create additional scar tissue. Some research links endometriosis to a modestly increased risk of certain ovarian cancers, though the absolute risk remains low. The condition is also associated with higher rates of autoimmune diseases, allergies, and chronic fatigue. Perhaps the most significant long-term impact for many people is the cumulative effect on quality of life: years of severe pain, disrupted sleep, missed work, and strained relationships.
How Treatment Approaches Compare
Because the underlying biology is so different, treatment strategies diverge significantly.
For PCOS, the first line of treatment is often lifestyle modification. Even modest weight loss (5 to 10% of body weight in those who are overweight) can improve insulin sensitivity, lower androgen levels, and restore more regular ovulation. Medications that improve insulin sensitivity are commonly prescribed. Hormonal birth control can regulate periods and reduce androgen-driven symptoms like acne and excess hair growth. When fertility is the goal, ovulation-inducing medications are typically the starting point.
Endometriosis treatment focuses on managing pain and slowing the growth of displaced tissue. Hormonal therapies that suppress estrogen, including certain birth control methods, can reduce symptoms by keeping the displaced tissue from cycling and bleeding each month. When pain is severe or fertility is affected, surgery to excise or ablate endometriosis lesions and remove scar tissue can provide significant relief, though symptoms recur in a meaningful percentage of people. For those who have completed childbearing and have severe, treatment-resistant disease, removal of the uterus and sometimes the ovaries may be considered, though this is a last resort.
It is possible to have both conditions at the same time. They arise from independent causes and having one does not protect against the other. If you have symptoms that seem to fit both descriptions, such as irregular periods alongside severe pelvic pain, it’s worth having both conditions evaluated separately.