What Is Photodynamic Therapy (PDT)? Treating Sun Damage Before It Becomes Skin Cancer

If you've been told you have actinic keratoses — the rough, scaly patches caused by years of sun exposure — photodynamic therapy (PDT) is one of the most effective ways to treat them, especially when there are multiple spots or a broad area of sun-damaged skin. Here's what the procedure actually involves.

What Is Photodynamic Therapy?

PDT is an in-office, non-surgical treatment that combines a topical photosensitizing medication with targeted light exposure. The medication makes damaged cells sensitive to light; when the treatment area is then illuminated, that light selectively destroys the abnormal cells while leaving surrounding healthy skin largely unaffected. It's FDA-approved and one of the few treatments that can address an entire area of sun damage — not just the spots that are visible — in a single session.

Two Light Options

OnSpot offers PDT with two different FDA-approved light sources, and your provider will recommend whichever best fits your skin and the extent of your sun damage:

Blue Light PDT uses the Levulan® Kerastick® (aminolevulinic acid) applied to the skin, followed by activation with BLU-U® blue light.

Red Light PDT uses AMELUZ® (aminolevulinic acid HCl) gel, applied by your provider and, after an incubation period, activated with the RhodoLED® red light. Red light PDT is FDA-approved for mild-to-moderate actinic keratoses of the face and scalp, and can treat an entire field of sun-damaged skin — including areas of damage that aren't visible as individual spots yet, not just the ones you can see.

What to Expect During Treatment

A PDT visit typically takes about 90 minutes total: the medication is applied to the treatment area, followed by an incubation period before the light activation itself. Some patients feel stinging or a burning sensation during the light-activation phase — this is temporary and fades shortly after treatment. Most patients see 70–80% clearance of treated actinic keratoses per session, and most patients only need 1–2 sessions to see significant results.

Aftercare and Downtime

Your skin will be sensitive to light for 24–48 hours after treatment, so plan to avoid direct sunlight and wear protective clothing during that window. It's normal to see redness, swelling, peeling, or scabbing at the treatment site as the skin heals — your provider will walk you through exactly what to expect and how to care for the area.

Why It Matters in Florida

Southwest Florida's year-round UV exposure makes cumulative sun damage one of the most common concerns our patients face. Actinic keratoses are precancerous, and a subset can progress to squamous cell carcinoma if left untreated. Because PDT can treat a whole area of damage rather than one spot at a time, it's often the most efficient option when sun damage is widespread rather than a single isolated patch.

Is PDT Right for You?

PDT is generally recommended for patients with multiple actinic keratoses or broader areas of sun damage, rather than a single isolated spot. Your dermatology professional will evaluate your skin and recommend whether PDT, cryotherapy, a topical medication, or another approach is the best fit — and if PDT is right for you, which light option makes the most sense for your treatment area.

Sources: American Academy of Dermatology; U.S. Food and Drug Administration; Skin Cancer Foundation.