Acanthosis nigricans is characterized by brownish darkening and velvety thickening of skin creases, most commonly in the armpits, neck, groin, knuckles, elbows and knees.
It is more common in teenagers and adults with darker skin, but can occasionally be seen in younger children if it is a family (inherited) trait. It often looks like the skin is dirty and cannot be cleaned. Small skin tags may be found within the dark areas. The most common cause is obesity (being overweight). It may also be seen in people with certain hormone problems such as diabetes, insulin resistance, or low thyroid. It can occur for no reason.
The treatment for acanthosis nigricans depends on the cause and consists of weight loss in overweight children, over the counter alpha hydroxy lotions (Lac-Hydrin 5%, Am Lactin 12%, Aqua Glycolic or Eucerin Plus), or treatment of the underlying hormone problem, if there is one.