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Photodynamic Therapy (PDT)

Light-activated treatment for actinic keratosis and field-damaged skin

Medically reviewed by Dr. Steven Q. Wang, MDLast reviewed

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What Is Photodynamic Therapy?

Photodynamic therapy (PDT) treats actinic keratosis (AK) using a two-step process instead of surgery or freezing. First, a photosensitizing solution — aminolevulinic acid (ALA) or its derivative, methyl aminolevulinate (MAL) — is applied to the skin and absorbed preferentially by damaged, sun-exposed cells. After an incubation period, the treated area is exposed to a specific wavelength of light (blue, red, or natural daylight), which activates the solution inside those cells and destroys them while largely sparing healthy surrounding skin.

Because PDT treats an entire area rather than a single spot, it's especially well suited for field cancerization — when years of sun exposure have damaged a broad area of skin, not just the AKs that are visible. This makes PDT a common choice for the face, scalp, and other areas with multiple or recurring AKs.

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Key Topics

Explore these topics to understand how PDT works, whether it's right for you, and what to expect before, during, and after treatment:

What is photodynamic therapy and how does it work?
The photosensitizer-and-light mechanism explained in plain language
Why might my dermatologist recommend PDT over other AK treatments?
Comparing PDT with cryotherapy and topical field therapy
Am I a good candidate for photodynamic therapy?
Who PDT is typically recommended for, and who may need a different approach
What happens during a PDT treatment session, step by step?
Preparation, photosensitizer application, incubation, and light exposure
How should I prepare for my PDT appointment?
What to do — and avoid — in the days before treatment
What side effects and downtime should I expect after PDT?
Redness, swelling, peeling, and the photosensitivity reaction timeline
How do I care for my skin after PDT?
Sun avoidance, wound care, and when to call your doctor
How many PDT sessions will I need, and what results can I expect?
Typical treatment courses, follow-up, and clearance rates
How is discomfort during PDT managed?
Cooling, timing, and other strategies clinics use to ease treatment
Is PDT safe, and who should avoid it?
Contraindications and rare risks to discuss with your dermatologist

When PDT May Not Be the Right Fit

PDT isn't the right choice for everyone. Your dermatologist will weigh factors such as:

  • •A history of a photosensitivity disorder, such as porphyria or lupus
  • •Use of certain medications that increase sensitivity to light
  • •Pregnancy or breastfeeding, out of caution
  • •Inability to avoid direct sunlight for 24–48 hours after treatment
  • •Very thick or deeply invasive lesions, which may need a different approach first

Who Is a Good Candidate

  • •Multiple AKs across a broad area (field cancerization)
  • •AKs on the face or scalp, where a good cosmetic outcome matters
  • •A history of AKs recurring despite spot treatment
  • •A preference to avoid a longer course of at-home topical medication
  • •Generally healthy skin, without a photosensitivity disorder

What to Expect at a Glance

  • •A single visit typically runs 1–3 hours, most of it incubation time
  • •Most people need 1–2 sessions, spaced about three weeks apart
  • •Redness, swelling, and peeling for about a week afterward
  • •Strict avoidance of direct sunlight for 24–48 hours post-treatment
  • •Visible improvement continues over several weeks

The PDT Treatment Course

A typical PDT treatment follows the same basic sequence regardless of which photosensitizer or light source your dermatologist uses:

  • •Preparation: the treatment area is cleansed and any thick scale is gently removed so the photosensitizer can penetrate evenly.
  • •Photosensitizer application: ALA or MAL is applied directly to the AKs and the surrounding sun-damaged skin.
  • •Incubation: the solution is left in place, typically for one to a few hours, so it can be absorbed by damaged cells.
  • •Light activation: blue light, red light, or natural daylight is used to activate the photosensitizer and destroy the treated cells.
  • •Follow-up: redness and peeling resolve over one to two weeks; a second session is sometimes scheduled a few weeks later.

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
  • 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

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

Printable Discussion Guide

Every question from the topics above, collected into one printable checklist — with a checkbox and space for notes beside each, and header fields for your appointment date and doctor's name.

Download the complete PDT discussion guide (PDF)

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