Acanthosis Nigricans

What Is It, Causes, Signs and Symptoms, and More

Author:Maria Emfietzoglou, MD

Editors:Alyssa Haag,Józia McGowan, DO,Kelsey LaFayette, DNP, RN, FNP-C

Illustrator:Jessica Reynolds, MS

Copyeditor:Stacy M. Johnson, LMSW

What is acanthosis nigricans?

Acanthosis nigricans refers to a condition characterized by dark discoloration and thickening of the skin. Although it can appear anywhere on the body, it typically affects the armpits, neck, and groin. Individuals may need medical advice as acanthosis nigricans is most commonly a sign of an underlying condition, such as insulin resistance, polycystic ovarian syndrome, or cancer. Once the management of the underlying condition is initiated, the skin’s condition is typically restored.  

Hyperpigmentation and thickening of the skin on back of neck and armpits.

What causes acanthosis nigricans?

Acanthosis nigricans is caused by various conditions that lead to the activation of growth factor receptors which stimulate the proliferation of skin cells, such as keratinocytes and fibroblasts, ultimately leading to darker skin. These conditions can be either benign or malignant.

Causes of benign acanthosis nigricans include insulin resistance when the cells in the liver, adipose tissue, and muscles become insensitive to insulin and its effects. Therefore, these cells become less capable of glucose intake from the bloodstream. Insulin resistance can ultimately develop into type II diabetes mellitus, another cause of acanthosis nigricans. Moreover, acanthosis nigricans can also occur in individuals with polycystic ovarian disease, a syndrome typically in those assigned to females at birth, characterized by symptoms related to excess androgen production (e.g., hirsutism, acne, insulin resistance, and irregular or absent menstrual cycles). Other benign causes include hypothyroidism, which occurs when there is a lack of thyroid hormones; and Cushing syndrome, which is a set of symptoms resulting from exposure to elevated levels of the stress hormone cortisol due to exogenous glucocorticoid medication use, a tumor of the adrenals or a tumor of the pituitary gland. Additionally, acanthosis nigricans has been associated with administering certain medications, such as oral contraceptives, corticosteroids, and vitamin supplements, like niacin

On the other hand, malignant acanthosis nigricans can be caused by various malignant tumors, such as stomach, colon, and liver cancer, as well as lymphoma. 

Finally, various factors can increase the risk of acanthosis nigricans, including positive family history and a personal history of obesity. 

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What are the symptoms of acanthosis nigricans?

Symptoms of acanthosis nigricans include dry, velvety, gray-brown hyperpigmented patches on the skin of body folds, such as the armpits and neck. Less frequently, acanthosis nigricans can appear in other skin sites or mucosal surfaces. The affected skin might also have tiny growths or skin tags and may be itchy or have an abnormal odor. 

How is acanthosis nigricans diagnosed?

Diagnosis of acanthosis nigricans starts with a thorough history and physical examination. Rarely a skin biopsy may be needed to confirm the diagnosis. Other tests may also be performed to identify the underlying cause, including blood glucose tests to diagnose insulin resistance and diabetes, as well as gonadal hormone levels (e.g., luteinizing hormone, follicular stimulating hormone, androstenedione)  and pelvic ultrasound to identify the polycystic ovarian syndrome. If hypothyroidism is the suspected underlying cause, thyroid hormone levels (e.g., TSH, T4) may also be measured. For Cushing syndrome, cortisol levels may be measured, and various imaging tests (e.g., abdomen CT) may be used. Finally, imaging tests, such as a CT scan, MRI, or gastrointestinal endoscopy, may also be used to exclude the possibility of a malignancy, especially in older adults with new-onset acanthosis nigricans without another identifiable cause. 

How is acanthosis nigricans treated?

Treatment of acanthosis nigricans primarily involves identifying and treating the underlying medical condition. Weight loss and antidiabetic medications (e.g., metformin) can help manage insulin resistance and diabetes mellitus. For polycystic ovarian syndrome, treatment may include oral contraceptives and metformin, a diabetic medication, to regulate the menstrual cycle; weight loss and antidiabetic medications, such as metformin, to improve insulin resistance; spironolactone to treat hirsutism, as well as clomiphene citrate to help induce ovulation if fertility is desired. Hypothyroidism can be managed with thyroid hormone supplementation, while treatment of Cushing syndrome may include either decreasing or discontinuing glucocorticoid medications or removing the tumor surgically or radioactively. Discontinuation of medications that are related to the condition may also be considered. In cases of cancer, surgery, chemotherapy, or radiotherapy may be necessary.

Treatment of the underlying cause will eventually restore the skin changes. For accelerated improvement, individuals may receive additional therapies for cosmetic purposes only. Topical al tretinoin gel can be applied to localized areas of acanthosis nigricans for up to two weeks. Vitamin D analogs, like calcipotriol cream, can be applied twice daily for three months. Finally, systemic retinoids, such as isotretinoin and acitretin, can be used in case of severe skin lesions. 

What are the most important facts to know about acanthosis nigricans?

Acanthosis nigricans is a skin condition characterized by dark patches of skin most commonly affecting body folds, such as the neck, armpits, and groin. Acanthosis nigricans is often a clinical feature of other underlying medical conditions, which can be either benign or malignant. Benign conditions include insulin resistance, diabetes mellitus, polycystic ovarian syndrome, thyroid disorder, adrenal gland disorders, and various medications. Malignant acanthosis nigricans can be due to multiple types of cancer, specifically stomach. Diagnosis is based on physical examination, focusing on identifying the underlying cause. Treatment is primarily based on the underlying cause but can also include additional therapies to accelerate the improvement of hyperpigmentation.

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Related links

Benign hyperpigmented skin lesions: Clinical practice
Pigmentation skin disorders: Pathology review

Resources for research and reference

Acanthosis nigricans. Mayo Clinic. Accessed May 24, 2022.

‌Acanthosis nigricans. National Health Service. Published June 1, 2021. Accessed May 24, 2022. 

Brady MF, Rawla P. Acanthosis nigricans. National Institute of Health. Accessed May 24, 2022.

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Hud JA Jr, Cohen JB, Wagner JM, Cruz PD Jr. Prevalence and significance of acanthosis nigricans in an adult obese population. Archives of Dermatology. 1992;128(7):941-944.

Nguyen TT, Keil MF, Russell DL, et al. Relation of acanthosis nigricans to hyperinsulinemia and insulin sensitivity in overweight African American and white children. Journal of Pediatrics. 2001;138(4):474-480. doi:10.1067/mpd.2001.112657

Rafalson L, Pham TH, Willi SM, Marcus M, Jessup A, Baranowski T. The association between acanthosis nigricans and dysglycemia in an ethnically diverse group of eighth grade students. Obesity (Silver Spring). 2013;21(3):E328-E333. doi:10.1002/oby.20129