Hormonal health

Acanthosis Nigricans: Skin's Insulin Resistance Signal

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Dark, velvety patches on the neck or in body folds are usually acanthosis nigricans, a sign of high insulin rather than poor hygiene. Excess insulin switches on growth signals in skin, so the patches can appear before blood sugar rises. In women, they often accompany insulin resistance, PCOS, and higher type 2 diabetes risk.

Last updated: July 2026

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What are these dark velvety patches on my neck?

Dark, velvety thickening in skin folds is called acanthosis nigricans, and it usually signals high insulin, not poor hygiene. The patches are typically symmetric, brown to gray-black, and soft or velvety to the touch, most often at the nape of the neck, the armpits, the groin, and under the breasts. They do not scrub off, because the color comes from thickened, more pigmented skin rather than dirt, and small skin tags often sit nearby. This change reflects insulin acting directly on skin cells 2. It is common in insulin resistance, polycystic ovary syndrome, and higher body weight, and less often it follows certain medications or other conditions. Our guide to insulin resistance symptoms covers the fuller picture these patches can point toward.

Why does insulin resistance darken the skin?

The patches form because excess insulin switches on growth signals in the skin. When cells throughout the body resist insulin's message, the pancreas compensates by making more of it, and those high insulin levels spill over onto receptors on skin cells, prompting them to multiply and deposit extra pigment. According to the Endocrine Society, acanthosis nigricans is a recognized marker of insulin resistance 2. Because the skin can register high insulin early, the patches sometimes appear months to years before fasting glucose or A1c climb into an abnormal range, which makes them a helpful warning 3. Recognizing them can prompt a metabolic check sooner, and our pages on prediabetes and early signs of type 2 diabetes explain what that check may involve.

Is this a sign of PCOS or diabetes?

Acanthosis nigricans commonly travels with polycystic ovary syndrome, prediabetes, and type 2 diabetes because insulin resistance underlies all three. In women, dark neck or fold patches with irregular periods, acne, or excess hair raise the question of PCOS, which affects about 1 in 10 women of reproductive age 14. The finding also flags a higher risk of type 2 diabetes, and the international guideline recommends checking blood sugar when it appears 3. Not everyone with these patches has diabetes; the change is tied to insulin resistance and weight. It can also show up between ages 10 and 16 around puberty's insulin surge, so noticing it early in a teen helps address metabolism sooner. See our overview of PCOS symptoms and PCOS and diabetes risk.

Can acanthosis nigricans fade?

The patches often lighten when the underlying insulin resistance improves, which is why treatment aims at the metabolism rather than the skin. Steady changes that improve insulin sensitivity, such as regular activity, balanced eating, and gradual weight change when appropriate, can soften and partially fade the patches over 3 to 6 months. When a clinician judges it useful, a medication that improves insulin sensitivity may be part of the plan, and our guide to losing weight with insulin resistance and the evidence on inositol for PCOS discuss supportive options. Topical lightening treatments do comparatively little, because they do not touch the cause. The most useful way to view acanthosis nigricans is as a signal to treat what is happening metabolically, not as a cosmetic blemish to cover.

When a clinician helps

A primary care clinician is worth seeing when dark velvety patches are new or spreading, when they come with weight change, or when they arrive alongside increased thirst, fatigue, irregular periods, or excess hair. They can order simple tests, such as fasting glucose, A1c, and hormone levels, to see whether insulin resistance, PCOS, or early diabetes is behind the skin change. Because the patches can appear before standard blood sugar tests turn abnormal, raising them is a reasonable prompt for screening. Our guide to when to get screened for diabetes can help you time that conversation. Nina Osei, NP, and the Gale team can help you prepare so the visit turns a skin observation into a clear metabolic check.

Common questions

They can be a warning sign. Acanthosis nigricans is strongly linked to insulin resistance, which raises the risk of type 2 diabetes, and the patches sometimes appear before blood sugar tests turn abnormal. Not everyone with them has diabetes, but they are a good reason to have your blood sugar checked.

No. The color is not dirt; it comes from thickened, more pigmented skin caused by high insulin, so scrubbing will not remove it and can irritate the area. The patches tend to lighten when the underlying insulin resistance improves, which is why the focus is on metabolism rather than cleansing.

Not on its own, but it is a common feature of PCOS. When dark neck or fold patches occur with irregular periods, acne, or excess hair, PCOS becomes more likely and is worth evaluating. A clinician can check hormones and blood sugar to sort out whether PCOS, insulin resistance, or both are present.

Often they fade partially when insulin sensitivity improves through activity, balanced eating, and, when appropriate, gradual weight change or medication a clinician recommends. Improvement usually takes months rather than days, and the patches serve as a useful marker of how the underlying metabolic picture is trending.

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When dark skin patches deserve a check

  • —New or spreading dark, velvety patches, especially with weight change, are a reason to seek clinician review for insulin resistance
  • —Dark patches alongside increased thirst, frequent urination, or unusual fatigue are a reason to seek evaluation for diabetes
  • —Skin darkening with irregular periods, acne, or excess hair is a reason to seek evaluation for PCOS
  • —Very sudden, widespread acanthosis nigricans that appears quickly is a reason to seek prompt medical evaluation

This article is general health education, not medical advice. Whether your skin change reflects insulin resistance, PCOS, or diabetes is a decision to sort out with a primary care clinician who can order the right tests.

References

  1. 1.Office on Women's Health (U.S. HHS) (2025). Polycystic ovary syndrome. Office on Women's Health (womenshealth.gov), U.S. HHS. link ✓States that PCOS affects about 1 in 10 women of reproductive age and features insulin resistance, and that darkening of the skin can accompany the condition.
  2. 2.Legro RS, et al. (Endocrine Society) (2013). Diagnosis and treatment of polycystic ovary syndrome: an Endocrine Society clinical practice guideline. Journal of Clinical Endocrinology & Metabolism. doi:10.1210/jc.2013-2350 ✓Endocrine Society PCOS guideline identifying acanthosis nigricans as a cutaneous marker of insulin resistance and a physical-exam finding in affected women.
  3. 3.Teede HJ, Tay CT, Laven J, et al. (International PCOS guideline consortium) (2023). Recommendations From the 2023 International Evidence-based Guideline for the Assessment and Management of Polycystic Ovary Syndrome. Journal of Clinical Endocrinology & Metabolism. doi:10.1210/clinem/dgad463 ✓International guideline documenting insulin resistance in PCOS and the increased risk of impaired glucose tolerance and type 2 diabetes, supporting glycemic screening.
  4. 4.American College of Obstetricians and Gynecologists (2018). ACOG Practice Bulletin No. 194: Polycystic Ovary Syndrome. Obstetrics & Gynecology. doi:10.1097/AOG.0000000000002656 ✓Describes the clinical features and evaluation of PCOS, including hyperandrogenism and metabolic assessment in women with irregular cycles.

4 sources, numbered by first appearance. General health information, not medical advice. AI-assisted editorial content — every citation independently verified. Editorial policy

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