Actinic Keratosis: Causes, Treatment, and When It Becomes Precancer

As of March 19, 2026.

Actinic keratosis is one of the most common reasons Canadians are referred to a skin specialist, and one of the most treatable conditions when it is caught early. These rough, scaly patches form on skin that has taken in years of ultraviolet (UV) radiation, and a portion of them can progress to squamous cell carcinoma (SCC) if they are ignored. This guide explains what actinic keratosis is, why it forms, how dermatologists treat it, and when a sun-damaged spot deserves a closer look. DermaDex is a Canadian healthtech company that builds artificial intelligence (AI) assisted tools to help patients and clinicians get skin concerns reviewed sooner.

This article is general information, not a diagnosis. If you have a changing, bleeding, or non-healing spot, see a clinician.

What is actinic keratosis?

Short answer: Actinic keratosis, also called solar keratosis, is a precancerous skin growth that appears as a rough, dry, scaly, or crusty patch on skin damaged by years of sun exposure. It is the most common precancer that dermatologists diagnose. The patches form in the outer layer of the skin when ultraviolet radiation damages skin cells called keratinocytes, and they are often easier to feel than to see, with a texture like fine sandpaper. Most people who develop one actinic keratosis go on to develop several, because the same sun exposure affects a wide area of skin rather than a single point.

The American Academy of Dermatology (AAD) classifies actinic keratosis as a precancer because a share of lesions can turn into skin cancer over time. Lesions show up most often on the face, scalp, ears, and the backs of the hands, and they tend to appear in adults over 40 who have accumulated decades of sun exposure. Some patches stay stable for years, while others grow, thicken, or change.

What causes actinic keratosis?

Short answer: Actinic keratosis is caused by cumulative ultraviolet (UV) exposure, mostly from the sun and from indoor tanning beds. The more lifetime UV your skin absorbs, the higher your risk. Both ultraviolet A (UVA) and ultraviolet B (UVB) wavelengths damage the DNA inside skin cells, and that damage adds up across decades, which is why the condition is most common in adults over 40 and on the body areas that catch the most sun. The World Health Organization (WHO) classifies solar UV radiation as a known human carcinogen. Fair skin, light eyes and hair, a history of sunburns, outdoor work, and a weakened immune system all raise the risk further.

Risk is not the same for everyone. The table below shows the factors dermatologists weigh when they assess how likely a person is to develop actinic keratosis.

Risk factor	Why it raises actinic keratosis risk
Fair skin (Fitzpatrick type I to II)	Less melanin means less natural protection from UV damage
Age over 40	Reflects decades of accumulated sun exposure
Outdoor work or recreation	More lifetime hours of UV exposure
History of indoor tanning or sunburns	Adds concentrated UV damage to skin cell DNA
Weakened immune system	Reduces the body's ability to repair and clear damaged cells

People with weakened immune systems, including organ transplant recipients, can develop actinic keratoses that are more numerous and that may progress faster, which is why this group is watched closely.

What does actinic keratosis look like and where does it appear?

Short answer: Actinic keratosis usually looks like a rough, dry, scaly patch a few millimetres to a couple of centimetres across, often pink, red, tan, or skin-coloured, on chronically sun-exposed skin. The most common sites are the face, ears, bald scalp, lips, neck, forearms, and the backs of the hands. Because the condition sits on sun-exposed skin, location is a strong clue. The patches are frequently easier to feel than to see, and some develop a thick, horn-like surface. Others itch, burn, or feel tender, and their colour and size can change over time. On the lips, the condition is called actinic cheilitis.

A spot that grows quickly, bleeds, becomes a sore that will not heal, or hardens into a firm lump can signal squamous cell carcinoma and should be examined promptly. Because actinic keratosis can also be confused with harmless growths, our guide on telling harmless spots from melanoma explains what dermatologists look for when they sort one from another.

Will actinic keratosis turn into cancer?

Short answer: Most individual actinic keratoses do not become cancer, and some clear on their own, but a meaningful share progress to squamous cell carcinoma (SCC), a common skin cancer. Because there is no reliable way to predict which lesions will progress, dermatologists generally treat them rather than wait and watch. Estimates for how often a single lesion becomes SCC vary widely in the research, from well under 1 percent to as high as 16 percent per lesion per year, according to a StatPearls review on the National Center for Biotechnology Information (NCBI) Bookshelf. The risk rises with the number of lesions and the years of accumulated sun damage.

The AAD reports that an estimated 40 to 60 percent of squamous cell carcinomas begin as untreated actinic keratoses. That link is why clinicians treat the lesions and keep watching the surrounding skin, rather than dismissing a rough patch as cosmetic. You can read more about that cancer in our overview of squamous cell carcinoma.

How is actinic keratosis treated?

Short answer: Treatment depends on how many lesions you have and where they are. Common options include cryotherapy (freezing with liquid nitrogen), prescription creams such as 5-fluorouracil, photodynamic therapy, and minor procedures like curettage. Most are done in a clinic and clear the great majority of lesions. Dermatologists separate care into lesion-directed treatment, which targets one or a few visible spots, and field treatment, which covers a larger area of sun-damaged skin where many lesions, including ones too small to see, are present. Cryotherapy alone clears roughly 67 to 99 percent of treated lesions depending on freeze time, according to the StatPearls review.

Treatment	How it works	Best suited for	What to expect
Cryotherapy (liquid nitrogen)	Freezes and destroys the lesion	One or a few visible spots	Stinging, a blister or scab, healing over 1 to 2 weeks
5-fluorouracil (5-FU) cream	Topical chemotherapy that targets abnormal cells	Many lesions across an area	Redness, crusting, and peeling for 2 to 4 weeks
Imiquimod cream	Activates the immune system against damaged cells	Field treatment of the face or scalp	Redness and inflammation over several weeks
Photodynamic therapy (PDT)	Light-activated solution destroys abnormal cells	Widespread or hard-to-treat areas	Burning during light exposure, redness for days
Curettage	Scraping the lesion, sometimes with cautery	Thick or horn-like lesions	A small wound that heals with a scab

The AAD notes there is no single best option for everyone, and the right choice is the one matched to your lesions and your skin. In Canada, in-office procedures such as cryotherapy and a diagnostic biopsy by a physician are generally covered by provincial health insurance like the Ontario Health Insurance Plan (OHIP) when they are medically necessary, while some prescription creams may carry a pharmacy cost depending on your drug coverage. Confirm the specifics with your clinic.

How can you prevent actinic keratosis in Canada?

Short answer: Prevention comes down to sun protection. Health Canada recommends broad-spectrum sunscreen of Sun Protection Factor (SPF) 30 or higher, shade during peak hours, protective clothing, and avoiding tanning beds. These steps lower the risk of both actinic keratosis and skin cancer. Canada's northern latitude does not remove ultraviolet (UV) risk, because the UV index climbs high in summer across the country, and snow, water, and sand reflect UV back onto the skin. The Canadian Dermatology Association (CDA), the Centers for Disease Control and Prevention (CDC), and Health Canada all give the same core advice on staying protected outdoors.

Protection step	What to do
Sunscreen	Use broad-spectrum SPF 30 or higher, apply generously, and reapply every 2 hours
Timing	Limit sun exposure between 11 a.m. and 3 p.m. when the UV index is highest
Clothing	Wear a wide-brimmed hat, sunglasses, long sleeves, and tightly woven fabric
Tanning beds	Avoid them entirely, since they deliver concentrated UVA and UVB

Reapply sunscreen after swimming or heavy sweating, and check the daily UV index before heading out, since it changes with season and cloud cover. Sun protection that starts in childhood lowers lifetime risk the most, but it helps at any age. For the screening side of prevention, see our guide on skin cancer screening in Canada.

When should you see a dermatologist about actinic keratosis?

Short answer: See a clinician if you have a rough, scaly patch that lasts more than a few weeks, a spot that grows, bleeds, or hurts, or many sun-damaged patches across an area. A dermatologist can confirm the diagnosis and treat lesions before they progress to skin cancer. Self-checks help, but actinic keratosis and early skin cancer can look alike, and a dermatoscope or a biopsy is sometimes needed to tell them apart. People at higher risk, including fair-skinned adults, outdoor workers, and organ transplant recipients, benefit from regular skin checks. Specialist wait times in parts of Canada can stretch for months, which delays both diagnosis and treatment.

DermaDex helps close that gap by connecting patients and primary-care clinicians to certified dermatologists for faster review of suspicious spots. If you have a concern you want looked at, contact our team. This article is general information and not a substitute for a hands-on medical assessment, so book a visit if a spot is changing or you are unsure.

Frequently asked questions about actinic keratosis?

Short answer: These are the questions Canadians most often ask about actinic keratosis, with brief evidence-based answers from a dermatologist. They cover whether the spots become cancer, the most effective treatments and creams, and the warning signs that mean a patch should be examined. None of this replaces a hands-on skin exam, so book a visit if a spot is changing, growing, or you are simply unsure about it.

Will actinic keratosis turn into cancer?

Most individual actinic keratoses will not turn into cancer, and some clear on their own. A portion, though, can progress to squamous cell carcinoma (SCC), a common skin cancer. Estimates for how often a single lesion progresses range from under 1 percent to as high as 16 percent per year in the research summarized by StatPearls on the NCBI Bookshelf. The American Academy of Dermatology reports that 40 to 60 percent of squamous cell carcinomas begin as untreated actinic keratoses. Because there is no reliable way to predict which lesions will progress, dermatologists generally treat them rather than wait. If a patch grows quickly, bleeds, or becomes a sore that will not heal, have it examined promptly.

What is the best treatment for actinic keratosis?

There is no single best treatment for everyone, and the right choice depends on how many lesions you have, where they are, and your skin. For one or a few spots, cryotherapy with liquid nitrogen is the most common in-office option and clears most treated lesions. When there are many lesions across an area of sun-damaged skin, dermatologists often choose field treatment with a prescription cream such as 5-fluorouracil (5-FU) or imiquimod, or photodynamic therapy. Thick, horn-like lesions may be scraped, a procedure called curettage. The American Academy of Dermatology stresses that the best option is the one matched to your specific case, chosen with your clinician. Many people use a combination of approaches over time.

When to worry about actinic keratosis?

Worry, and seek care, when a spot changes. Warning signs include a patch that grows quickly, becomes thick or firm, bleeds, itches or hurts, or turns into a sore that does not heal. Any of these can signal a shift toward squamous cell carcinoma. You should also act if you have many lesions, if you are immune-suppressed for example after an organ transplant, or if a previously treated spot returns. A single stable, rough patch is lower risk, but because actinic keratosis and early skin cancer can look similar, a dermatologist's exam is the reliable way to tell them apart. When in doubt, get it checked rather than watch it for months.

What is the best cream for actinic keratosis?

The prescription cream most often considered the strongest for field treatment is 5-fluorouracil (5-FU), a topical chemotherapy that targets abnormal cells across an area of skin. Other effective options include imiquimod, which works through the immune system, diclofenac gel, and tirbanibulin. Each has a different schedule and side-effect pattern, and 5-FU and imiquimod typically cause weeks of redness, crusting, and peeling as they work, which is expected. There is no single best cream for every patient. The choice depends on the number of lesions, their location, your skin, and how much visible reaction you can manage. A dermatologist matches the cream to your case, and over-the-counter moisturizers or acid creams are not a substitute for prescription treatment.

Sources

• American Academy of Dermatology (AAD), "Actinic keratosis: Overview."
• American Academy of Dermatology (AAD), "Actinic keratosis: Diagnosis and treatment."
• American Academy of Dermatology (AAD), "Squamous cell carcinoma of the skin."
• StatPearls, "Actinic Keratosis," National Center for Biotechnology Information (NCBI) Bookshelf.
• Centers for Disease Control and Prevention (CDC), "About Skin Cancer."
• Centers for Disease Control and Prevention (CDC), "Skin Cancer Prevention."
• Health Canada, "Sun safety."
• World Health Organization (WHO), "Ultraviolet radiation."
• Canadian Dermatology Association (CDA), "Sun protection."