PCOS Dark Patches on Skin Explained

If you have PCOS, you may have noticed velvety, darkened patches of skin appearing on your neck, armpits, inner thighs, or even your knuckles. This is called acanthosis nigricans, and it is one of the most visible signs that your hormones and blood sugar regulation are under stress. Understanding PCOS dark patches on skin goes beyond cosmetic concern: these changes are meaningful signals from your body worth paying close attention to.

This condition affects a significant proportion of people with PCOS, and yet it is one of the most under-discussed symptoms. For a broader foundation on how PCOS affects your hormones, metabolism, and cycle, start with our complete guide to PCOS before diving deeper here.

What Is Acanthosis Nigricans in PCOS?

Acanthosis nigricans in PCOS is a skin condition causing dark, thickened, velvety patches, most commonly on the neck, underarms, and skin folds. It develops when elevated insulin levels stimulate excess skin cell and pigment production. It is not a rash or infection, but a visible marker of insulin resistance commonly seen in PCOS.

The name comes from Latin: "acanthosis" means spiny thickening, and "nigricans" means darkening. The patches may feel slightly raised and have a rough or velvety texture when you run your finger across them. In people with lighter skin tones, they appear as tan or brown areas. In deeper skin tones, they may appear as deeper brown or almost black patches, which is why PCOS skin discoloration is often noticed first in women of colour.

It is important to understand that this is not a hygiene issue. Many people scrub vigorously at the areas, believing them to be dirty, but no amount of exfoliation will remove them if the underlying hormonal cause is not addressed.

What Causes Dark Patches on PCOS Skin?

PCOS dark patches on skin are primarily caused by hyperinsulinaemia, a state of chronically elevated insulin. Excess insulin binds to receptors in the skin, triggering overgrowth of skin cells and melanocytes, which produce pigment. Elevated androgens in PCOS further amplify this skin response, making acanthosis nigricans particularly common in this population.

Here is what happens at the cellular level. When insulin levels are persistently high, insulin acts on receptors in the dermis and epidermis that stimulate keratinocyte (skin cell) proliferation. This leads to the characteristic thickening. At the same time, insulin-like growth factor 1 (IGF-1) is also elevated in many women with PCOS, and this compound independently drives melanocyte stimulation, deepening the colour of the patches.

Research published by the National Institutes of Health confirms that acanthosis nigricans is strongly correlated with hyperinsulinaemia and insulin resistance across multiple populations, making it a useful clinical marker when diagnosing metabolic dysfunction in PCOS.

Androgens also play a role. In PCOS, excess testosterone and other androgens can directly stimulate sebaceous glands and skin cells, contributing to both the texture and colour changes. You can read more about how androgens drive many of PCOS's physical symptoms in our article on androgens and your cycle.

"Acanthosis nigricans should be viewed as a clinical window into metabolic health. When we see it in a young woman with PCOS, it tells us that insulin resistance is likely already present and needs to be addressed, not just for her skin, but for her long-term cardiovascular and reproductive health."

Dr. Andrea Dunaif, MD, Chief of the Hilda and J. Lester Gabrilove Division of Endocrinology, Diabetes, and Bone Disease, Icahn School of Medicine at Mount Sinai

Where Does Dark Neck PCOS Skin Most Commonly Appear?

The back and sides of the neck are the most common sites for PCOS-related acanthosis nigricans, followed by the armpits, groin folds, inner thighs, elbows, and knuckles. These skin folds and friction areas have higher concentrations of insulin receptors, making them more sensitive to the effects of elevated insulin levels.

The dark neck in PCOS is often the first sign that prompts women to seek answers. Many describe noticing a shadow-like discolouration when looking in the mirror or when others point it out. The underarms (axillae) are the second most common location, and this is often where the texture change is most noticeable.

Less commonly, patches can appear on the:

• Knuckles and finger joints
• Around the belly button
• Under the breasts
• Around the lips or vulva in more severe cases

The severity and spread of the patches can indicate the degree of insulin resistance. Mild cases may show only faint discolouration at the nape of the neck, while more pronounced insulin resistance can produce extensive, deeply pigmented areas across multiple sites.

How Does Insulin Resistance Drive PCOS Skin Discoloration?

Insulin resistance in PCOS means cells stop responding effectively to insulin, prompting the pancreas to produce more. This excess insulin does not only affect glucose metabolism: it also activates receptors in skin tissue, triggering the chain reaction that produces the dark, thickened patches of acanthosis nigricans seen in PCOS skin discoloration.

Think of insulin resistance as a broken lock and key system. Your cells are the locks, and insulin is the key. When the locks stop working properly, your body makes more keys, flooding the system. Those extra keys then accidentally open other doors, including doors in your skin that should not be opened.

A study from the Journal of Clinical Endocrinology and Metabolism found that women with PCOS who had acanthosis nigricans showed significantly higher fasting insulin levels and homeostatic model assessment of insulin resistance (HOMA-IR) scores compared to PCOS women without skin changes, underlining the direct metabolic link.

For a deeper understanding of how insulin resistance shapes your entire hormonal picture, our article on insulin resistance and your cycle is essential reading.

Can Acanthosis Nigricans Be Reversed?

Yes, acanthosis nigricans can improve significantly or even reverse fully when the underlying cause is addressed. In PCOS, this means reducing insulin resistance through dietary changes, movement, stress reduction, and in some cases medication or targeted supplementation. The skin changes can take months to fade but do respond when metabolic health improves.

This is genuinely good news. The patches are not permanent scarring. Because they are driven by circulating insulin levels, bringing those levels down allows the skin cells to return to a more normal turnover rate, and the pigmentation gradually lightens.

Approaches that can support this process include:

Dietary Strategies

Reducing refined carbohydrate intake and prioritising protein, fibre, and healthy fats at each meal helps blunt post-meal insulin spikes. Choosing lower glycaemic index foods and spacing meals thoughtfully can have a meaningful effect on fasting insulin levels over time. Our PCOS-friendly snacks for blood sugar article has practical ideas for keeping levels stable throughout the day.

Movement and Exercise

Resistance training and moderate aerobic exercise both improve insulin sensitivity by increasing the number of GLUT4 transporters in muscle cells. Even 30 minutes of brisk walking five times a week has been shown to reduce fasting insulin in women with PCOS.

Targeted Supplements

Myo-inositol, in particular, has strong evidence for improving insulin sensitivity in PCOS. Research published via PubMed Central has shown that myo-inositol supplementation can significantly reduce fasting insulin and improve hormonal markers in PCOS. Berberine and magnesium are also worth considering with professional guidance.

Topical Approaches

While topical treatments do not address the root cause, retinoid creams, alpha-hydroxy acids (AHAs), and vitamin C serums may help visually lighten the patches. Dermatologists may also recommend prescription tretinoin for more pronounced cases. These should be used alongside, not instead of, metabolic interventions.

"We see acanthosis nigricans fade in our PCOS patients when they consistently work on their insulin sensitivity. It can take six to twelve months, but the skin genuinely responds. It is one of the most motivating visible markers of metabolic improvement we have in clinical practice."

Dr. Lara Briden, ND, Naturopathic Doctor and Author of Period Repair Manual, Queensland, Australia

Is Acanthosis Always a Sign of Insulin Resistance?

Not always, but in the context of PCOS, acanthosis nigricans is most commonly linked to insulin resistance and hyperinsulinaemia. In rare cases, it can also be associated with certain medications, thyroid dysfunction, or other endocrine disorders. A very small number of acanthosis nigricans cases are linked to internal malignancy, though these cases are uncommon and present quite differently.

In PCOS specifically, the overwhelming majority of acanthosis nigricans cases are metabolic in origin. Other potential (though less common) triggers include:

• Hypothyroidism: low thyroid function can also contribute to skin changes and insulin dysregulation
• Cushing syndrome: excess cortisol can produce similar skin changes
• Lipodystrophy: abnormal fat distribution affecting insulin signalling
• Certain medications: including systemic corticosteroids, niacin at high doses, and some oral contraceptives

If you have noticeable acanthosis nigricans and have not yet had your fasting insulin, fasting glucose, and HOMA-IR tested, this is worth discussing with your healthcare provider. These tests give you a clearer picture of where your metabolic health stands.

What Else Should You Know About PCOS Skin Discoloration?

Acanthosis nigricans is not the only skin manifestation of PCOS. Many women also experience:

• Hormonal acne, particularly along the jawline and chin
• Skin tags (acrochordons), which often appear in the same areas as acanthosis nigricans and share the same insulin-driven mechanism
• Hirsutism (excess facial or body hair) driven by androgens
• Dry or oily patches as sebaceous gland activity is disrupted

When multiple of these symptoms are present together, they collectively point toward a pattern of elevated androgens and insulin resistance that is characteristic of PCOS. Addressing the hormonal root causes rather than treating each skin symptom in isolation is what creates lasting change.