Actinic keratosis is a rough, scaly patch on the skin caused by years of sun exposure. These patches develop when ultraviolet radiation damages skin cells enough to make them grow abnormally, but not yet aggressively enough to be classified as skin cancer. More than 40 million Americans develop actinic keratoses each year, making them one of the most common reasons people visit a dermatologist. They matter because a small percentage of these lesions can progress into squamous cell carcinoma, a type of skin cancer.
How Sun Damage Creates These Lesions
The outer layer of your skin is made up of cells called keratinocytes. When UV radiation hits these cells repeatedly over years, it damages their DNA in ways that disrupt normal growth and turnover. Instead of maturing and shedding like healthy skin cells, the damaged keratinocytes begin to pile up and multiply in a disorganized way. This abnormal buildup is what forms the rough, scaly patch you can see or feel on the surface.
At the molecular level, UV exposure triggers mutations in a gene called TP53, which normally acts as a brake on abnormal cell growth. Researchers have found TP53 changes in virtually all actinic keratosis samples, even in areas that look normal under a microscope. This suggests the damage starts well before a visible lesion appears. The surrounding skin that looks healthy may already carry mutations, a concept called field cancerization. It’s the reason dermatologists sometimes treat a broader area of skin rather than just the visible spots.
Actinic keratoses sit on a spectrum between normal sun-damaged skin and squamous cell carcinoma. Their mutational burden falls somewhere in between: more genetic damage than ordinary sun-exposed skin, less than a full-blown cancer. In some cases, a gene involved in cell growth becomes amplified, pushing the lesion closer to cancer. This progression isn’t inevitable, but it’s unpredictable for any individual spot, which is why treatment is generally recommended.
What Actinic Keratosis Looks and Feels Like
The hallmark of actinic keratosis is texture. These patches feel rough or gritty, like sandpaper, and they’re sometimes easier to detect by running your fingers across the skin than by looking in a mirror. They typically appear as flat or slightly raised patches covered with dry, adherent scales. The borders tend to be poorly defined, blending into the surrounding skin rather than forming a sharp edge.
Color varies. Most lesions are pink to reddish, but pigmented versions can appear brown or even black, which can make them harder to distinguish from other skin spots. A less common variant called a cutaneous horn produces a cone-shaped, hard projection that’s white to yellowish. Lesions can be single or multiple, and they range from a few millimeters across to larger than a centimeter. Dermatologists generally consider any lesion over 1 cm worth biopsying to rule out progression.
The most common locations are areas that get the most cumulative sun exposure: the face, ears, bald or thinning scalp, the back of the neck, the tops of the forearms, and the backs of the hands. If you’ve spent decades outdoors, even casually, these are the spots to watch.
Cryotherapy: The Most Common In-Office Treatment
For individual spots, most dermatologists reach for liquid nitrogen first. The procedure takes seconds: a brief spray or application freezes the abnormal tissue, which blisters and peels away over the following days. You can expect swelling within 12 to 36 hours, followed by a blister that crusts over and heals gradually. Healing time depends on how deeply the spot was frozen and where it is on your body. The face and backs of the hands, where older skin is thinner and more sun-damaged, often take longer.
Cure rates for cryotherapy vary with technique. Freeze times under 5 seconds clear about 39% of lesions at three months, while freezing for over 20 seconds pushes clearance up to 83%. When the freeze depth is carefully controlled, cure rates approach nearly 100% at six weeks. The tradeoff is that deeper freezes heal more slowly and are more likely to leave a lighter patch of skin behind.
Topical Treatments for Broader Areas
When you have many lesions spread across a wider area, or when the surrounding skin likely harbors invisible damage, topical medications treat the entire field rather than spot by spot. Several options are available, and they differ mainly in how long you use them and how much skin irritation to expect.
- Fluorouracil 5% cream is applied twice daily for two to four weeks. It works by killing rapidly dividing abnormal cells. Your skin will become red, raw, and crusty during treatment, which is a sign it’s working. The irritation resolves after you stop.
- Imiquimod 3.75% cream stimulates your immune system to attack abnormal cells. The typical schedule is two two-week cycles with a two-week rest in between. Redness and inflammation are common.
- Diclofenac 3% gel is an anti-inflammatory applied twice daily for 60 to 90 days. It’s gentler than other options but requires a much longer treatment course.
- Tirbanibulin 1% ointment is the newest option, applied once daily for just five consecutive days. The shorter course makes it more convenient, though it treats a limited area (about the size of a credit card per course).
All of these creams cause temporary skin reactions, from mild redness to significant peeling and discomfort. The appearance during treatment can be alarming, but the inflammation is part of the process and typically resolves within a few weeks of finishing.
Photodynamic Therapy
Photodynamic therapy, or PDT, uses a combination of a light-sensitive chemical and a specific wavelength of light to destroy abnormal cells. A cream is applied to the affected skin and left to absorb for a set period. The abnormal, rapidly growing cells take up more of the chemical than healthy cells do. When the skin is then exposed to blue light (for shallow lesions like actinic keratoses) or red light (for thicker growths), the chemical activates and produces molecules that kill the cells from within.
The advantage of PDT is its selectivity: it targets diseased tissue while largely sparing normal skin. It treats both visible lesions and the surrounding field of subclinical damage. The main downsides are that the treatment area becomes very sensitive to light afterward, and many people experience significant stinging or burning during the light exposure. Some redness and peeling follow for several days.
Why Treatment Matters
No one can predict which actinic keratosis will progress to squamous cell carcinoma and which will stay harmless or even regress on its own. That uncertainty is exactly why dermatologists recommend treating them. The field cancerization concept adds another layer: the skin around a visible lesion is already primed with UV-induced mutations, so even cleared spots can recur if the surrounding area isn’t addressed.
Treated or not, anyone with actinic keratoses needs regular skin checks going forward. New spots will continue to appear as long as cumulative sun damage exists in the skin, and having had actinic keratoses is a strong signal that your skin has absorbed enough UV to be at ongoing risk.
Preventing New Lesions
Daily sunscreen use does more than prevent sunburns. In a clinical trial comparing regular sunscreen users to a control group, the sunscreen group developed 38% fewer new actinic keratoses. They also had more existing lesions fade away on their own. The relationship was dose-dependent: the more consistently people applied sunscreen, the fewer new lesions appeared and the more old ones resolved.
Beyond sunscreen, protective clothing, wide-brimmed hats, and avoiding peak sun hours all reduce cumulative UV exposure. For people who already have actinic keratoses, these measures won’t undo existing damage, but they meaningfully slow the rate at which new spots develop. Given that treatment for each new lesion involves either a freezing session or weeks of topical cream, prevention pays off in a very practical way.