Unlike most skin conditions caused by the sun, actinic keratosis (AK), which is sometimes called solar keratosis, is usually benign. At least 90 percent of these small, scaly skin spots will not turn into cancer, says Sean R. Christensen, MD, PhD, a Yale Medicine dermatologic surgeon and an associate professor of dermatology at Yale School of Medicine.

“Actinic keratosis is an abnormal growth of cells caused by long-term damage from the sun,” he says. “They are not cancerous, but a small fraction of them will develop into skin cancer. Because we don’t know which ones will become cancer and which will not, dermatologists recommend treatment of these lesions,” Dr. Christensen says.

With highly specialized expertise in diagnosing and treating skin cancer, Yale Medicine is a referral-based tertiary care center. This means that dermatologists from other practices send their most challenging, worrisome cases to us for analysis and treatment. "We have had the experience of dealing with thousands of unusual cases over the years," says Kathleen Suozzi, MD, associate professor of dermatology and a faculty member in the Section of Dermatologic Surgery and Cutaneous Oncology.

Actinic keratoses are often referred to in the plural form because people rarely develop just one. The small bumps typically appear on the parts of the body that are most exposed to the sun's rays such as the ears, nose, cheeks, temples and bald scalp. They can also appear on the forearms and backs of hands and usually look like rough bumps or patches on the skin.

“They often have a sandpaper-like feel to them,” Dr. Christensen explains. They start off small and slowly grow in size until they’re about an eighth to a quarter of an inch. The spots don’t cause pain, but they occasionally itch or feel tender. The growths may be scaly or crusty or they may resemble warts, although they're not quite as thick. “I tell patients that if you notice any new growth on your skin that doesn't heal in about one month, you should get it checked out,” says Dr. Christensen

AK is caused by the accumulation of sun exposure over time, says Dr. Christensen. It's very common in adults 55 years old and over, especially those who have spent a lot of time working or exercising outdoors (for example, construction workers, boaters and tennis players).

It's slightly more common in men than women because they are less likely to use adequate sun protection. Age is a risk factor as is having fair, light-colored skin. But the incidence of skin cancer is on the rise among younger people, so it is possible for AK to occur in people in their 30s and 40s. People with olive or darker-colored skin can also develop skin cancer.

Patients will often notice a rough spot that isn't going away and ask their dermatologist to take a look at it. Most of the time, the doctor can make a visual diagnosis, and in the cases that are less obvious, will do a biopsy. The spots are only biopsied if they look like an actual skin cancer or if they don’t respond to initial treatment, says Dr. Christensen.

Patients will often notice a rough spot that isn't going away and ask their dermatologist to take a look at it. Most of the time, the doctor can make a visual diagnosis, and in the cases that are less obvious, will do a biopsy. The spots are only biopsied if they look like an actual skin cancer or if they don’t respond to initial treatment, says Dr. Suozzi.

Yale Medicine’s Dermatologic Surgery Program focuses on diagnosing and treating skin cancer, explains Dr. Christensen. He has lectured at the American Academy of Dermatology Annual Meeting, educating dermatologists around the world about treating regions of skin that have developed multiple cancerous and precancerous lesions.

Because the Dermatologic Surgery Program is a referral-based, tertiary-care program, area dermatologists send the team their most puzzling or most serious cases.

“Most cases of AK can and should be treated by a general dermatologist,” says Dr. Christensen. “Every exception to the rule, every case that goes a little wrong or patient that doesn't respond in a typical way to the standard therapies—those are the patients that we see the most."

Yale Medicine Dermatology also has on-site photodynamic therapy machines and a wide range of laser treatments that aren't widely available in community dermatologist offices, says Dr. Suozzi.

"We also have the knowledge and experience to recognize that a patient may respond better to a different, nonstandard type of treatment,” Dr. Christensen says, “including combination therapy or surgical treatment when appropriate.”

Finally, Dr. Christensen strongly recommends sun protection, in addition to medical therapy, for patients with multiple actinic keratoses.

“We know that continued sun exposure causes more AK to develop, and we know that regular use of sunblock can cause many AK to regress or disappear,” he says. “Even if you have had a lot of sun damage over the years, it’s never too late to help your skin in the fight against skin cancer.”