Actinic keratosis

by Allison Osmond, MD FRCPC
March 6, 2023

What causes actinic keratosis?

AK is a very common condition caused by long-term exposure to the sun.  AK commonly occurs on the face, lips, ear, back of the hands, arms, and scalp.  However, AK can develop anywhere on the body where the skin has been exposed to the sun for long periods of time.  When similar changes affect the lips, it is called actinic cheilitis. It is not uncommon for people to have multiple areas of the skin with actinic keratoses. Older age, fair skin, and chronic sun exposure are risk factors for developing AK.

How do pathologists make this diagnosis?

When examined without a microscope, AK typically has a scaly red appearance. The diagnosis is usually made after a small tissue sample is removed in a procedure called a biopsy. The tissue same will then be sent to a pathologist for examination under the microscope.

What does actinic keratosis look like under the microscope?

AK starts in the cells at the very bottom of the epidermis which are called basal cells. When examined under the microscope, the abnormal cells in AK look bigger, and darker, and appear more disorganized compared to the more superficial squamous cells.

This picture shows actinic keratosis viewed under the microscope.

What are the variants of actinic keratosis and why is the variant important?

Pathologists divide AK into groups called variants based on how the cells look under the microscope. The most common variants of AK are called acantholytic, pigmented, hypertrophic, and Bowenoid. Bowenoid type AK is important because it is associated with a higher risk of changing into a type of cancer called squamous cell carcinoma over time. For this reason, Bowenoid type AK needs to be completely removed in order to reduce the risk of developing cancer.