What Causes Actinic Keratosis?

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Above All, Sun Exposure

Chronic sun exposure is the cause of almost all actinic keratoses. Sun damage to the skin is cumulative, so even a brief period in the sun adds to the lifetime total. Cloudy days aren’t safe either, because 70-80 percent of the sun’s ultraviolet (UV) rays can pass through clouds. These harmful rays can also bounce off sand, snow and other reflective surfaces, giving you extra exposure.

The more time you spend in the sun over the years, the greater your odds of developing one or more AKs, so older people and outdoor workers are at increased risk. The incidence is slightly higher in men, because they tend to spend more time in the sun and use less sun protection than women do. Though some individuals as young as in their 20s are affected, AKs are much more common in people over age 50. Some experts believe that almost everyone over 80 has AKs.

Location makes a difference: The closer to the equator you live, the more likely you are to have actinic keratoses. 

Other Causes

The ultraviolet radiation given off by the lamps in a tanning salon can be even more concentrated and dangerous than the sun, so dermatologists warn against indoor tanning. The more tanning you do, the higher your odds of developing AKs.

Occasionally, actinic keratoses can also be caused by extensive exposure to X-rays or a number of industrial chemicals.

Who Is Most at Risk?

People with fair skin, freckles, blonde or red hair and blue, green or gray eyes are most vulnerable to sun damage. They have a high likelihood of developing AKs if they spend time in the sun and live long enough. African Americans, Hispanics, Asians and others with darker skin are not as susceptible as Caucasians, but anyone can develop skin cancers. (You can identify your skin type here). In fact, partly because of later detection, skin cancers in African Americans and Hispanics are more likely to be found at an advanced stage than those found in Caucasians.

Individuals whose immune defenses are weakened by cancer chemotherapy, AIDS, organ transplantation or other factors are less able to fight off the effects of ultraviolet radiation and thus more likely to develop actinic keratoses. You should also be aware that extensive UV exposure itself suppresses the immune system, reducing its ability to repair UV damage.

Medical Reviewers:
Mark Lebwohl, MD
Deborah S. Sarnoff, MD