Acanthosis nigricans

Acanthosis nigricans is a skin condition that causes patches of darker, thicker, and often velvety-feeling skin, usually in body folds — the neck, armpits, groin, elbows, and knees. It's not contagious and not harmful on its own, but it's often a visible sign of something worth checking: most commonly insulin resistance, prediabetes, or type 2 diabetes.

Why it matters

In India, acanthosis nigricans is a useful early signal — noticed on the neck, it's often the first visible sign of insulin resistance and a significant risk of developing type 2 diabetes. Seeing it should prompt checking blood sugar and lifestyle review.

Causes

• Insulin resistance / prediabetes / type 2 diabetes — the most common cause
• Obesity
• Hormonal conditions — PCOS, thyroid disorders, Cushing's syndrome
• Certain medicines — oral contraceptives, corticosteroids, niacin
• Family history / genetic forms
• Rarely, a sign of internal cancer — usually when it appears suddenly, spreads quickly, or affects areas like palms and mouth

What to do

• See a doctor to identify the cause — especially to check blood sugar and weight
• Treating the cause is the main treatment — weight loss improves insulin resistance, which often lightens the patches over time
• Skin creams can help cosmetically but don't address the cause
• If it appears suddenly or in unusual places, get it assessed — rare underlying conditions may need further investigation