Acanthosis is a word pathologists use to describe an increase in the thickness of the top layer of the skin. It is a common non-cancerous change that can occur anywhere on the body.
The surface of the skin is called the epidermis. The epidermis is made up mostly of specialized cells called squamous cells. The normal thickness of the epidermis varies throughout the body.
Pathologists use the word acanthosis when the epidermis looks thicker than normal for that area of the body. It is a descriptive term for what is seen under the microscope and not a diagnosis although it is often used to help make a diagnosis.
Used alone, acanthosis is different than the diagnosis “acanthosis nigricans” which refers to a velvety thickening of the skin when examined without a microscope. Unlike acanthosis, acanthosis nigricans does not show thickening of the epidermis when examined under the microscope.
The squamous cells give the skin its strength and acanthosis is often a response to ongoing and chronic irritation of the skin. Common conditions associated that show acanthosis include: