How many PDT sessions does actinic keratosis usually need?

Most people complete one or two PDT sessions, typically spaced about two to four weeks apart. A single session may be enough for a smaller area with few lesions, while broader field damage or thicker actinic keratoses often benefits from a second treatment. Your dermatologist will assess the treated area at a follow-up visit and decide whether more sessions or a different approach would help.

How effective is PDT at clearing actinic keratosis?

Clinical studies generally report that a large majority of treated actinic keratoses clear after a standard PDT course, with complete clearance rates commonly cited in the range of roughly 70 to 90 percent for thinner lesions, somewhat lower for thicker ones. Combining PDT with a topical field treatment such as imiquimod has been shown to improve clearance further. Results vary by lesion thickness, body site, and the specific PDT protocol used.

Can actinic keratosis come back after PDT?

Yes. PDT treats the actinic keratoses present at the time of treatment and reduces the overall burden of sun-damaged cells in the treated field, but it doesn't reverse a lifetime of cumulative sun exposure or prevent new damage going forward. New actinic keratoses can develop later, especially without consistent sun protection, which is why routine skin checks and daily sunscreen remain important after PDT.

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How Many PDT Sessions Will I Need, and What Results Can I Expect?

Typical treatment courses, follow-up, and realistic clearance rates

Medically reviewed by Dr. Steven Q. Wang, MDLast reviewed September 4, 2026

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Download printable checklist (PDF)

Introduction

Once you and your dermatologist decide photodynamic therapy (PDT) is the right approach for your actinic keratosis (AK), the next practical questions are usually: how many sessions will this take, and how well is it likely to work? The honest answer is "it depends" — on how many lesions you have, how thick they are, where they're located, and the exact protocol your dermatologist uses — but there are well-established patterns you can use to set realistic expectations.

This article covers the typical number and spacing of PDT sessions, what happens at your follow-up visit, published clearance rates, why some lesions may need re-treatment, how long results tend to last, and why ongoing skin checks still matter afterward.

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The Typical Treatment Course

Most people undergoing PDT for actinic keratosis complete one or two sessions:

•A single session is sometimes enough, especially for a limited area with thinner, less-developed AKs.
•Two sessions, spaced roughly two to four weeks apart, are common practice — particularly for broader field cancerization or thicker lesions, since a second treatment targets any cells that survived the first round.
•More extensive field damage — a large area of chronically sun-damaged skin with numerous AKs — may call for additional sessions over time, sometimes as part of an ongoing maintenance plan rather than a single fixed course.
•The exact number and spacing depends on the photosensitizer and light source used, the body site treated, and how your skin responds — your dermatologist will tailor this to you.

The Follow-Up Visit

A few weeks after your final session, your dermatologist will examine the treated area to assess how well the AKs have cleared. This visit typically involves:

•A visual and tactile skin exam of the treated field, comparing it to the pre-treatment appearance.
•Identification of any lesions that remain rough, scaly, or otherwise still present.
•A decision about next steps for anything that didn't fully clear — this might mean a repeat PDT session, a different field treatment, or a targeted procedure such as cryotherapy for a specific stubborn spot.
•A plan for how soon you should return for your next routine skin check.

What the Evidence Says About Clearance Rates

Published studies on PDT for actinic keratosis report favorable but variable clearance rates, generally in the range of about 70 to 90 percent complete clearance for thinner lesions after a standard course, with somewhat lower rates for thicker or more hyperkeratotic AKs that light penetrates less easily.

A 2019 meta-analysis pooling ten randomized controlled trials found that combining PDT with a topical field treatment — such as imiquimod, 5-fluorouracil, or a retinoid gel — improved both participant-level and lesion-level clearance compared with PDT alone. This is one reason your dermatologist might recommend pairing PDT with a topical medication for extensive or recurrent field damage rather than relying on PDT by itself.

Keep in mind that reported rates come from clinical trial populations and specific protocols; your individual results depend on your lesions, skin type, and treatment details. Ask your dermatologist what to realistically expect in your own case.

If a Lesion Doesn't Fully Clear

Not every AK responds fully to a single PDT course. If a lesion remains after follow-up, your dermatologist has several options:

•Repeating PDT on that area
•Adding a topical field therapy alongside or after PDT
•Switching to a spot treatment like cryotherapy for a persistent lesion
•Taking a biopsy if a lesion looks or feels atypical, to rule out progression

How Long Results Last

Successfully cleared AKs generally stay cleared, but PDT doesn't undo the underlying sun damage in the surrounding skin. Over time:

•Many people enjoy months to a few years of improvement in the treated field.
•Some studies suggest field-directed therapies like PDT may reduce the rate of new AKs forming compared with no treatment.
•Durability varies by how much cumulative sun exposure the skin has had and how consistently sun protection is followed afterward.

New AKs Can Still Form — Why Ongoing Skin Checks Matter

It's important to set the right expectation: PDT reduces your current burden of actinic keratosis and sun-damaged cells, but it does not eliminate your future risk. If you've had enough cumulative sun exposure to develop AKs once, the surrounding skin — and any skin that continues to be sun-exposed — remains susceptible to new ones forming over time.

That's why a successful PDT course is best thought of as one part of an ongoing skin-health plan, not a one-time fix. Daily broad-spectrum sunscreen, sun-protective clothing, and routine dermatology visits for a full skin exam remain just as important after PDT as before it — both to catch new AKs early and because a personal history of AK is itself a marker of higher skin cancer risk overall.

What to Ask Your Doctor

Download printable checklist (PDF)

Based on my lesions, how many PDT sessions do you expect I'll need?
When will you check whether the treatment worked, and what will that visit involve?
What clearance rate is realistic for someone with my skin and lesion type?
If some lesions don't clear, what would be the next step?
How long do you expect these results to last for me?
How often should I have routine skin checks going forward?

Conclusion

Most people need one or two PDT sessions, spaced a few weeks apart, followed by a check-in visit to confirm how well the treatment worked. Published clearance rates are encouraging — often in the range of 70 to 90 percent for thinner lesions — though your own results depend on the specifics of your skin and treatment plan.

Just as important: PDT treats the AKs present today, not your future risk. Continued sun protection and regular skin checks are what keep new actinic keratosis, and more serious skin cancers, from taking hold down the road.

Sources

Clinical Guidelines & Peer-Reviewed Literature

Eisen DB, Asgari MM, Bennett DD, et al. Guidelines of care for the management of actinic keratosis. J Am Acad Dermatol. 2021;85(4):e209-e233. PubMed
Heppt MV, Steeb T, Leiter U, Berking C. Efficacy of photodynamic therapy combined with topical interventions for the treatment of actinic keratosis: a meta-analysis. J Eur Acad Dermatol Venereol. 2019;33(5):863-873. PubMed
Wiegell SR, Wulf HC, Szeimies RM, et al. Daylight photodynamic therapy for actinic keratosis: an international consensus. J Eur Acad Dermatol Venereol. 2012;26(6):673-679. PubMed

Patient Resources

American Academy of Dermatology (AAD) — Actinic Keratosis: Diagnosis and Treatment
Memorial Sloan Kettering Cancer Center — Photodynamic Therapy

Disclaimer: This page is for educational purposes only and is not a substitute for professional medical advice. Always consult a qualified dermatologist about your own diagnosis, treatment plan, and expected results.

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