Skin -

Actinic keratosis

This article was last reviewed and updated on August 8, 2019
by Allison Osmond, MD FRCPC

Quick facts:

  • Actinic keratosis is a non-cancerous skin disease.

  • It is a very common condition caused by long term exposure to the sun.

  • There are different types of actinic keratosis and some types are considered a pre-cancerous condition because they can turn into a type of cancer called squamous cell carcinoma.


Normal skin

Skin is made up of three layers: epidermis, dermis, and subcutaneous fat. The surface and the part you can see when you look at your skin is called the epidermis. The cells that make up the epidermis include: squamous cells, basal cells, melanocytes, Merkel cells, and cells of the immune system. The squamous cells in the epidermis produce a material called keratin which makes the skin waterproof and strong and protects us from toxins and injuries. 

The dermis is directly below the epidermis. The dermis is separated from the epidermis by a thin layer of tissue called the basement membrane. The dermis contains blood vessels and nerves. Below the dermis is a layer of fat called subcutaneous adipose tissue.

  What is actinic keratosis?

Actinic keratosis is a non-cancerous disease that affects the squamous cells in the epidermis. When viewed through a microscope, the epidermis is made up of several layers of squamous cells stacked one on top of another, like the bricks in a house. 


Actinic keratosis starts in the cells at the very bottom of the epidermis which are called basal cells. In actinic keratosis, the basal cells look bigger, darker, and appear more disorganized compared to the more superficial squamous cells.

Actinic keratosis is a very common condition caused by long term exposure to the sun.  Actinic keratosis commonly occurs on the face, lips, ear, back of the hands, arms and scalp.  However, actinic keratosis can develop any where on the body where the skin has been exposed to the sun for long periods of time. It is not uncommon for people to have multiple areas of the skin with actinic keratoses.

When you have actinic keratosis, you or your doctor might notice an area of the skin that looks scaly or red.  When similar changes affect the lips, it is called actinic cheilitis. When viewed through the microscope, actinic keratosis and actinic cheilitis look the same. Older age, fair skin, and chronic sun exposure are risk factors for developing actinic keratosis.

Types of actinic keratosis

Pathologists divide actinic keratosis in groups called variants based on how the cells look under the microscope. 


Variants of actinic keratosis include:

  • Acantholytic - When examined under the microscope, the cells in this type of actinic keratosis look like they are separated from each other by a small empty space.

  • Pigmented - This type looks dark when examined under the microscope because the cells contain a pigment called melanin. 

  • Hypertrophic - In this type of actinic keratosis, the epidermis is thicker than normal. 

  • Bowenoid - In this type of actinic keratosis, the abnormal cells fill the entire epidermis.

Why is this important? Bowenoid actinic keratosis is very important because it is considered a pre-cancerous disease that can, over time, turn into a cancer called squamous cell carcinoma.


For this reason, Bowenoid actinic keratosis needs to be completely removed in order reduce the risk of developing cancer and to avoid recurrence.

Depending on the type of actinic keratosis your have, or if you have multiple, your doctor may treat you with a cream to apply to your skin or light therapy (in addition to your biopsy).

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