The most common cause of acanthosis nigricans is being very overweight.
Other causes include:
- type 2 diabetes
- conditions that affect hormone levels – such as Cushing’s syndrome, polycystic ovary syndrome or an underactive thyroid
- taking certain medicines – including steroids or hormone treatments like the contraceptive pill
- rarely, cancer – usually stomach cancer
- rarely, a faulty gene inherited from your parents
Sometimes healthy people with no other conditions get acanthosis nigricans. This is more common in people with black or brown skin.