Acanthosis Nigricans in itself is not dangerous nor does it either require or even have a specific treatment. It looks a bit odd, but that’s about it. Sometimes Acanthosis Nigricans simply happens and no one quite knows why. However, a much more important point is that there are a number of possible underlying causes, some of them serious, like cancer or diabetes.

Acanthosis nigricans (AN) is a skin condition characterized by
abnormally increased coloration (hyperpigmentation) and "velvety"
thickening (hyperkeratosis) of the skin, particularly of skin fold
regions, such as of the neck and groin and under the arms (axillae).
Various benign (non-cancerous) forms of AN have been identified in
which the disorder may be inherited as a primary condition or
associated with various underlying syndromes; an excess accumulation of
body fat (obesity); or the use of certain medications (i.e.,
drug-induced AN). In other instances, AN may occur in association with
an underlying cancerous tumor (i.e., malignant AN).

The actual symptoms are:

Acanthosis nigricans usually appears slowly and doesn’t cause any symptoms other than skin changes.

Eventually, dark, velvety skin with very visible markings and
creases appears in the armpits, groin, and neck. Sometimes, the lips,
palms, soles of feet, or other areas may be affected.

The important thing about Acanthosis Nigricans is that i you don’t already have one of the commonly known causes of it thn you need to be checked out for all of th other known causes. I can be a sign of highly serious underlying and as yet unknown problems.

One thought is that it is a possible sign of the onset of diabetes, the symptoms themselves being a sign of a changing resistance to insulin.

Experts suggest that AN may be a skin manifestation of insulin
resistance, which is a condition characterized by impaired biological
responses to insulin. Insulin, a hormone produced by the pancreas,
regulates blood glucose levels by promoting the movement of glucose
into cells for energy production or into the liver and fat cells for
energy storage. (Glucose is a simple sugar that is the body’s primary
source of energy for cell metabolism.) Some clinicians suggest that
insulin resistance causes a build-up of the hormone in the blood, and
then it finds its way into skin cells. Insulin resistance may be
associated with various disorders, including obesity and
non-insulin-dependent (type II) diabetes mellitus. In individuals with
type II diabetes mellitus, the pancreas produces insulin but the body
becomes resistant to its effects, leading to insufficient absorption of
glucose and abnormally increased glucose levels in the blood
(hyperglycemia) and urine. As a result, there may be a gradual onset of
certain symptoms, including excessive urination (polyuria) and
increased thirst (polydipsia), and the development of particular
complications without appropriate treatment.

Shorter version: acanthosis nigricans in itself is nothing to worry about. But get checked out to see what’s causing it as there are some serious and treatable diseases of which it can be a symptom.