PCOS: What It Is, Why It Happens, How It Is Diagnosed

If you experience irregular periods, persistent acne, unwanted hair on your face or body, and a body that no longer responds as it used to, then polycystic ovary syndrome (PCOS) could be one of the factors involved.

PCOS is one of the most common hormonal disorders in women, occurring in about one in eight cases, although many people do not receive a definite explanation. The following guide outlines what PCOS is, why it occurs, and how it is diagnosed, based on the most recent international evidence.

What is PCOS?

PCOS is a common, long-term hormonal and metabolic condition and can have an effect on the way your ovaries function as well as on your skin, your weight, your mood and your long-term health. Although it is called PCOS, the condition is not caused by ovarian cysts.

If you are diagnosed with PCOS, you may have two of these symptoms after other causes are ruled out:

1. Irregular or absent ovulation
2. A blood test can detect high androgen levels (for example, hormones such as testosterone), or you may notice signs such as excessive hair growth or acne.
3. Polycystic ovaries on an ultrasound scan, or a raised AMH (anti-Müllerian hormone) level in adults

PMOS is the new name. In May 2026, an international consensus decided to rename PCOS as polyendocrine metabolic ovarian syndrome (PMOS) to highlight its effects on the entire body more accurately. The new name will be introduced gradually over the coming years. For now, ‘PCOS’ will still be encountered most frequently, which is why we continue to use it in this guide.

Symptoms

PCOS varies from person to person; some have several symptoms, while others notice only one or two. It’s not necessary to have all the symptoms listed here to have PCOS, and the presence of one does not mean that you do.

Irregular or absent periods

This is typically the first sign: you don’t menstruate regularly, either they become infrequent, or they stop altogether.

If it’s been more than three years since your first period, your cycles are considered irregular if:

• they’re shorter than 21 days or longer than 35 days
• you have fewer than eight periods a year
• any single cycle lasts longer than 90 days

For the first 1 to 3 years after menstruation begins, cycles of up to 45 days are still possible. Irregular periods are a normal aspect of puberty.

Note if your periods become infrequent or stop completely. If you don’t ovulate regularly, your uterine lining won’t shed as often as it should and will tend to become thicker. Your doctor will be able to help keep it in good condition, typically by using hormonal treatment to induce a regular bleeding episode.

Excess hair and acne

High androgen levels can leAdd to hirsutism is the presence of coarse, dark hair on the face, chest, abdomen, or back. Moreover, androgens cause the skin to produce more oil, which in turn can result in acne that persists, especially along the jawline, chin, and lower cheeks, and which does not improve with normal skincare.

Since both are medical symptoms, not cosmetic ones, and since both can be treated, it’s a good idea to mention them to your doctor.

Weight changes

Many people who have PCOS find it easier to gain weight and more difficult to lose it, particularly around the waist, a condition that is due to insulin resistance and not because of a lack of effort. PCOS occurs in people of all body sizes, including those who are slim.

Hair thinning

The androgens that cause increased body hair can also cause scalp thinning, typically appearing as thinning at the crown or a broader parting rather than a receding hairline; this condition is called female-pattern hair loss.

Fertility

PCOS is the leading cause of infertility in cases of irregular ovulation, and a large number of women only discover that they have it when they begin trying to have a child. The good news is that ovulation can generally be recovered with treatment, and most women with PCOS are capable of getting pregnant.

The symptoms that are often missed

• Dark, velvety areas on your neck, in your armpits, or in your groin (a condition known as acanthosis nigricans) indicate insulin resistance.
• Fatigue and bad sleep. Since PCOS is associated with an increased risk of obstructive sleep apnoea, this is particularly true if you snore or if you feel drowsy during the day.
• A low mood and anxiety are both more frequently seen in cases of PCOS, and the international guidelines advise that doctors should check for them.
• There is a difficult relationship with food and, since disordered eating is also more common in cases of PCOS, it is important to talk about it openly.

If any of these seem familiar, tell your doctor about them along with your periods and skin changes. They are part of the same condition, and this helps your doctor get a complete picture.

What causes PCOS

There isn’t one single cause. PCOS develops from several factors working together, and researchers are still uncovering how they connect.

Insulin resistance

Insulin helps your body move sugar from your blood into your cells. With insulin resistance, your cells respond less well, so your body makes more insulin to compensate. High insulin levels prompt your ovaries to produce more androgens, which disrupts ovulation.

Insulin resistance is common in PCOS, regardless of your body size. Lean women can have it too, and excess weight can make it worse.

Androgens

Androgens are hormones that everyone produces, but people with PCOS tend to make more of them. Higher levels interfere with how follicles mature in your ovaries, so an egg isn’t released regularly. They also cause the skin and hair symptoms of PCOS.

Genetics

PCOS often runs in families. If your mother or sister has it, your chances of having it are higher. Researchers have identified several genes linked to the condition, but no single gene causes it, and there’s no genetic test to diagnose it.

What does NOT cause PCOS

PCOS is not caused by anything you did or didn’t do. It isn’t the result of your diet, a lack of exercise, stress, or taking the pill. Weight gain can make symptoms more noticeable, but it isn’t the root cause, and losing weight won’t make PCOS disappear. Understanding this matters because blame often stops people from seeking the care they deserve.

How PCOS is diagnosed

No single test diagnoses PCOS; your doctor will review your medical history, perform an exam, run tests, and rule out other conditions that may look similar.

The Rotterdam criteria explained.

If you are an adult, your doctor will diagnose PCOS if you have at least two of these three symptoms:

• Irregular or absent ovulation. This usually means your periods are irregular.
• High androgen levels. You might notice extra hair growth, acne, or thinning hair on your scalp. Sometimes, this shows up as raised levels on a blood test.
• Polycystic ovaries on an ultrasound, or a higher-than-usual AMH level.

In that case, if you already have irregular cycles and signs of high androgens, you would not need a scan or an AMH test.

The rules for adolescents are stricter. In their case, both irregular cycles and high androgen levels must be present. Ultrasound and AMH are not used since the young ovaries naturally have a large number of follicles. If only one of these features is present, your doctor might say you are “at risk” and will review your situation later.

Blood tests

If you take the combined pill, your androgen results won’t be reliable. If a blood test is needed to confirm the diagnosis, your doctor may suggest stopping hormonal contraception for at least three months first, using another form of contraception in the meantime.

You may have seen the LH: FSH ratio or fasting insulin mentioned online. Current guidelines don’t recommend either for diagnosing PCOS, because the results vary too much to be reliable.

Ultrasound

A transvaginal ultrasound counts the small follicles in each ovary. Polycystic ovarian morphology means 20 or more follicles in either ovary, or an ovarian volume of 10 mL or more. Ultrasound isn’t used within eight years of your first period.

Why “polycystic ovaries” on a scan alone is not PCOS

The “cysts” seen on a scan aren’t true cysts. They’re small follicles that have paused in their development. Plenty of women with regular cycles and no symptoms have ovaries that look like this, especially in their teens and twenties. Research linked to the renaming of the condition found no increase in abnormal ovarian cysts in PCOS.

This works both ways. A scan alone can’t diagnose PCOS, and you can have PCOS with completely normal-looking ovaries.

The Four PCOS Phenotypes

Since two out of the three symptoms are required for a diagnosis, PCOS can show itself in four different combinations, known as phenotypes. Although many articles omit this point, it does affect how your care is organised.

Why it matters:

• The classic forms of PCOS, which are known as phenotypes A and B, are generally associated with the greatest risk of insulin resistance, type 2 diabetes, and heart problems.
• Since Phenotype A has regular cycles, it is easy to miss, even though high androgens still increase metabolic risks.
• Phenotype D generally has the mildest metabolic profile when androgen levels are not high.

Your doctor can use your phenotype to determine how closely to monitor your metabolic health and which symptoms to watch first. Nevertheless, regular health checks are still advisable regardless of your phenotype.

PCOS vs endometriosis

Both conditions are common, can affect fertility, and are usually not diagnosed until later. Yet they work very differently.

Endometriosis occurs in about one in ten women of reproductive age, and it usually takes many years to reach a diagnosis. Diagnosis has recently changed. Instead of considering keyhole surgery (laparoscopy) as the gold standard, international guidelines now regard scans as being able to identify endometriosis and allow treatment to start based on the symptoms presented. Surgery is now used only when scans are clear, but symptoms persist after treatment.

You can have both conditions. So, if you are experiencing irregular periods together with severe pelvic pain, you should ask your doctor to consider both possibilities.

PCOS vs thyroid problems

The symptoms of an underactive thyroid (hypothyroidism) include irregular periods, weight gain, tiredness, and hair thinning, all of which are similar to those seen in PCOS. That’s why each PCOS evaluation includes a TSH blood test.

The two conditions can occur at the same time, and in some cases having an underactive thyroid can lead to symptoms that appear to be due to PCOS. To learn more about the differences between them, see our guide on thyroid and hormonal imbalance.

Long-Term Health

PCOS is a lifelong condition and its effects extend well beyond your periods. By understanding the risks, you and your doctor can anticipate and manage them.

• Type 2 diabetes: People with PCOS are more likely to have impaired glucose tolerance and type 2 diabetes no matter what their age or weight is. When you are diagnosed, your blood sugar levels should be checked, and then every one to three years, respectively. For Asian women, the risk level is considered to be higher at a lower BMI (above 23 rather than 25), a factor that is pertinent in Singapore.
• Heart health: Women with PCOS have higher blood pressure and cholesterol levels and a greater risk of suffering from cardiovascular disease. Regularly checking your blood pressure, weight, and cholesterol helps detect changes early.
• Endometrial health: If periods occur infrequently, then the lining of the uterus does not shed regularly, and this increases the risk of endometrial cancer, although the overall risk is still low. Treatment that causes regular bleeding helps to protect the lining, so you should let your doctor know if there are long gaps between your periods or if you are experiencing unusual bleeding.
• Pregnancy: Because of PCOS, the risk of developing gestational diabetes and high blood pressure during pregnancy increases, and as a result, your medical team may start to check your blood sugar earlier.
• Mental health and sleep: People with PCOS are more likely to experience low mood, anxiety, and sleep apnoea, and all of these conditions can be treated.

Treatment overview

At the moment there is no cure for PCOS, but it is possible to manage your symptoms well and reduce your long-term risks. The course of treatment you receive will depend on the symptoms you have, your phenotype, and whether or not you are trying to get pregnant.

Lifestyle

Everyone with PCOS should follow a healthy eating plan and stay active, regardless of their weight. There is no one specific “PCOS diet”. The best approach is the one you can stick to. If you have excess weight, losing 5 to 10 per cent can improve your cycles, ovulation, and blood sugar levels. Aim for at least 150 minutes of moderate physical activity each week, along with muscle-strengthening exercises on two days.

Medication

• The oral contraceptive pill used in combination is generally the first option when dealing with irregular periods, excess hair, and acne; it also helps to protect the lining of the womb.
• Metformin improves insulin resistance and helps with metabolic symptoms; you can take it with the pill.
• Anti-androgens, such as spironolactone, can help promote hair growth or improve acne when the pill alone is not enough. Reliable contraception must be used when taking them since they are not safe during pregnancy.
• For some adults who have PCOS and excess weight, weight-loss drugs (GLP-1 receptor agonists) could be taken together with changes to their lifestyle. However, they must be discontinued before one attempts to conceive.
• Inositol is a commonly used supplement, but the evidence supporting it is very limited and unclear. Although it is usually well tolerated, talk to your doctor about it, and do not use it as a replacement for established treatment.

Fertility-specific treatment

• Letrozole, which is a tablet used to induce ovulation, can also be used with clomiphene and metformin, even though the latter two are less effective.
• If the tablets are ineffective, then gonadotrophin injections or a procedure known as laparoscopic ovarian drilling should be carried out.
• Third line: IVF, or earlier if other factors affect fertility.

Living with PCOS: what a long-term care plan looks like

PCOS changes as you move through life, so your care plan should change too. Here’s what a good long-term plan can look like for you:

• A yearly review of your weight, blood pressure, and symptoms
• Blood sugar checks every one to three years, and cholesterol checks based on your risk.
• Regular check-ins on your mood and wellbeing
• Support with fertility planning when you’re ready, including a blood sugar check before or early in pregnancy
• Evaluating the treatment you receive as your priorities change, for example from dealing with acne in your twenties to focusing on heart health later in life

Androgen-related symptoms generally improve after menopause, but the metabolic risks persist, and therefore regular check-ups are still important. Many people find the best care comes from a team that may include a general practitioner, a gynaecologist, an endocrinologist, and a dietitian.

When to see a doctor

Book an appointment if you notice:

• cycles shorter than 21 days or longer than 35 days, or fewer than eight periods a year
• no period for three months or more
• new or worsening excess hair, acne, or scalp hair thinning
• dark, velvety patches of skin
• difficulty getting pregnant after 12 months of trying, or after 6 months if you’re 35 or older
• ongoing tiredness, low mood, or anxiety alongside any of the above

Hint: For a few months before your appointment, keep a record of your cycles and symptoms. A clear record will help your doctor spot patterns and may speed up the diagnostic process.

Frequently Asked Questions

References: 

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7. Teede, H. J., Khomami, M. B., Morman, R., Laven, J. S. E., Joham, A. E., Costello, M. F., Patil, M., Rees, D. A., Berry, L., Cree, M. G., Zhao, H., Norman, R. J., Dokras, A., Piltonen, T., & Global Name Change Consortium. (2026). Polyendocrine metabolic ovarian syndrome, the new name for polycystic ovary syndrome: A multistep global consensus process. Lancet, 407(10545), 2329–2339. https://doi.org/10.1016/S0140-6736(26)00717-8 
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Reviewed By

Dr. Rabia kakatikar
Embryologist

Dr. Rutuja Raundal
Gynaecologist/Fertility Specialist
Cosmetic Gynaecologist

Anna Haotanto

Anna Haotanto is the Founder of Zora Health and a passionate advocate for women’s empowerment. Anna’s personal experiences with egg-freezing, PCOS, perimenopause and the challenges of fertility have fueled her mission to provide high-quality information, financing, and support to help women and couples navigate their fertility journeys with confidence. She is also recognised for her achievements in finance, entrepreneurship, and women’s empowerment, and has been featured in various media outlets. You can also follow her on Linkedin or Instagram.