A dark patch of skin around the neck, underarms, or groin can be easy to brush off. Many people assume it is dirt, shaving irritation, or normal rubbing from clothing. But when the area does not wash away and feels thicker or almost velvety, it may be worth paying closer attention.
One possible explanation is acanthosis nigricans, a common skin change that can appear in body folds. It is not a sign of poor hygiene, and scrubbing the skin usually will not fix it. In some cases, it may be connected to how the body is handling insulin.
What Acanthosis Nigricans Can Look Like
Acanthosis nigricans often shows up as darker skin that feels thicker, rougher, or velvety to the touch. It commonly develops in areas where skin folds or rubs together, including the neck, armpits, and groin.
The patches may not hurt or itch, which is one reason people can ignore them for a long time. Because the change can be gradual, it may not seem important at first.