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Definition  

Acanthosis nigricans is a skin condition in which brown or black velvet-like markings appear under the arms, in the groin, or on the back of the neck. Any skin fold can be affected, including the lower lip and chin.

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Causes  

Causes of acanthosis nigricans may include:

  • High insulin levels in people who are obese
  • A family history of acanthosis nigricans
  • A cancerous tumor—rare