Actinic keratosis: the sun-damage patches that are a warning, not yet a cancer
Last updated September 3, 2026.
Actinic keratoses are rough, scaly patches caused by years of sun damage: pre-cancerous changes (a small fraction, left untreated, can progress to squamous cell skin cancer), extremely common on sun-exposed skin in fair people past middle age, and easily treated. They are a warning light, not a cancer: clearing them is simple (freezing, creams, or light therapy), and their real message is that your skin has taken enough sun to need lifelong protection and watching.
What do they look and feel like?
Small (millimeters to a centimeter or two), rough, gritty, sandpapery patches (often easier felt than seen: run a finger over the scalp, ears, face, backs of hands, or forearms), pink, red, or skin-colored, sometimes with a hard scale or horn, occasionally tender. They come in crops on the sun-exposed sites (the bald scalp, the ears, the nose, the hands), on a background of sun-damaged skin. The distinction to care about: the patch that thickens, ulcerates, bleeds, or grows fast may have turned: that one gets the urgent look.
Why do they happen?
Cumulative ultraviolet damage over decades: the sun (and the sunbeds) injuring the skin's cells until some grow abnormally. The risk profile: fair skin that burns easily, the outdoor decades (work or sport), the sunny-climate years, age (rare under 40, common over 60), the immunosuppressed (transplant patients especially: their keratoses behave worse and their surveillance is tighter), and the male-pattern bald scalp. They are the skin's ledger of the sun it has seen: the childhood burns included.
What actually clears them?
- Freezing (cryotherapy): the standard for individual patches: liquid nitrogen, a sting, a scab, gone: done in the surgery in seconds.
- The field creams: for the skin peppered with many (treating the whole sun-damaged field, including the ones you cannot yet see): fluorouracil, imiquimod, and the others, working over weeks with a predictable inflamed phase.
- Photodynamic therapy: the cream-plus-light treatment for the widespread kind, effective and with good cosmetic results.
- Surgery or scraping for the thick ones, with a biopsy whenever there is doubt about what it is.
- The lifelong protection after: daily sunscreen on the exposed sites, the hat, the sleeves, the midday-sun sense: and the regular skin checks.
When is it urgent?
The transformation signs (the patch becoming a cancer): rapid growth, thickening or hardening markedly, ulcerating or bleeding without healing, a tender growing nodule, or a non-healing sore: prompt (days, not months) dermatology assessment. Everything else about actinic keratosis is routine clinic medicine. The daily sunscreen is the habit that pays from today. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
What a Pymander AI doctor consult looks like
Illustrative example, not a real member's messages.
Common questions
Is this skin cancer?
No: it is the step before, and the distinction carries the whole management: actinic keratoses are pre-cancerous (the sun-damaged cells are abnormal but confined and not yet behaving as cancer), and the numbers are genuinely reassuring: the large majority never turn (a rough estimate is a few percent per patch over years, and many simply stay or regress), while the cancer a rare one becomes (squamous cell carcinoma) is itself highly curable when caught early, which is exactly what the watching achieves. The sensible frame: you do not have skin cancer; you have documented proof that your skin has had enough sun for the cancer question to be worth monitoring, and the treatment plus the sunscreen plus the checks is the complete answer to that proof.
Why did the doctor freeze them? Does that fix it?
Cryotherapy (liquid nitrogen) is the standard treatment for individual actinic keratoses: the freeze kills the abnormal cells, the patch blisters, scabs, and heals over two to three weeks, and it clears the treated lesion in the large majority (a stubborn one occasionally needs a second freeze or a switch of method). What it does not do: it treats the patch, not the sun-damaged field it grew from (the surrounding skin carries the same decades of damage and the seeds of future patches), which is why new keratoses can appear nearby (new arrivals, not the old one returning), and why the sunscreen-and-checking habit after treatment is the second half of the prescription. The freeze fixes the lesion; the habits manage the field.
What are the field creams and why do they look so angry?
For skin peppered with many keratoses, the field treatments (the prescription creams: fluorouracil, imiquimod, and similar) treat the whole sun-damaged area, visible patches and the invisible ones, over weeks of application: and the angry phase is the treatment working (the abnormal cells inflame, redden, and crust while the healthy skin sails through: the worse your field, the more dramatic the fortnight, which patients should be warned to expect rather than fear). The payoff after the inflammation settles: the field cleared, fewer new keratoses for years, and often visibly rejuvenated skin. Photodynamic therapy (cream activated by light) is the cousin with the same logic. The alternative framing: one rough fortnight versus years of patch-by-patch freezing.
What signs mean one has turned into a cancer?
The transformation list, worth keeping: a patch that grows rapidly (weeks rather than the keratosis's years), thickens or hardens into a nodule (the gritty patch becoming a lump), ulcerates or bleeds without healing (a sore that will not close), becomes tender or painful, or develops a horn or crust that keeps reforming. Any of these earns a prompt appointment (days to a couple of weeks, not the annual check), because the squamous cell cancer they announce is very curable early and harder late. The rest of the watching is gentle: the monthly finger over the scalp and hands (feel is better than sight for these), and the annual professional skin check. Knowing the list is how you never need it too late.
Do I really need sunscreen every day now, forever?
Yes, and the reasoning is specific to you now: your skin has proven (with four lesions) that its sun ledger is full, and every further dose adds to the field the keratoses grow from; daily sunscreen on the permanently exposed sites (the scalp or the hat, the face, the ears, the backs of the hands) is the single highest-yield habit, with the evidence that consistent use in sun-damaged skin genuinely reduces new actinic keratoses and squamous cancers. The practical version that survives daily life: a moisturizer-with-SPF by the toothbrush (habit-stacked, no thought), the brimmed hat by the door for the outdoor work (your scalp is your highest-risk site), and the reapplication on the genuinely outdoors days. It is the prescription that prevents the next freezing appointment.
Am I now at higher risk of melanoma too?
The risk picture has nuance worth understanding: actinic keratoses flag cumulative sun damage (the chronic, decades-of-exposure kind), which links mainly to the squamous and basal cell cancers, while melanoma links more to the intense burning exposures (the childhood and holiday burns); but the honest summary is that anyone with actinic keratoses has a sun-damaged, fair, at-risk skin, and the surveillance habit should cover everything: the monthly self-check (the gritty patches for the keratosis-turned-SCC, the changing moles for melanoma: new, changing, bleeding, or the odd-one-out mole earns the prompt appointment), and the annual professional check where your GP judges it useful. One habit, all the doors watched. The sun protection you now adopt protects against every one of them.