Photodynamic therapy (PDT) with Blu-U blue light is one of the most effective field treatments available for actinic keratoses — particularly for patients with widespread or numerous precancerous lesions across large areas of sun-damaged skin. It combines high lesion clearance rates with meaningful improvement in the overall texture and appearance of chronically sun-damaged skin, making it useful both medically and cosmetically.
The treatment builds on the principle of selective photosensitization. Actinic keratoses and other rapidly dividing or metabolically active skin cells absorb a photosensitizing agent more readily than normal tissue. When that agent is then activated by a specific wavelength of light, it produces a chemical reaction that destroys the abnormal cells while leaving the surrounding normal tissue relatively spared.
How the treatment works
The photosensitizing agent — aminolevulinic acid (ALA), sold as Levulan or the newer nanoemulsion formulation Ameluz — is applied to the treatment area in the office. The skin then incubates for one to two hours to allow the ALA to be absorbed and metabolized into the active photosensitizer by the target cells. Ameluz has shown higher clearance rates than Levulan in head-to-head trials, attributed to better skin penetration.
After incubation, the area is exposed to the Blu-U light source for a defined treatment period — typically 15 to 17 minutes. The light activates the photosensitizer within the abnormal cells, generating reactive oxygen species that destroy them.
The treated area then undergoes a visible inflammatory reaction — redness, swelling, and peeling — over 24 to 48 hours, resolving over one to two weeks. This reaction is expected and reflects the treatment working. Patients need to understand this in advance so they can plan around it. The final result, once the skin has healed, typically shows both clearance of visible AKs and improvement in the overall quality of the surrounding sun-damaged skin.
Photosensitivity precautions
The photosensitizing agent remains active in the skin for 40 to 48 hours after application. During this window, any sun exposure — including through window glass — can cause a severe phototoxic reaction. Strict indoor light avoidance for 48 hours after treatment is not optional. We review this thoroughly before scheduling and confirm that patients can accommodate it. In Florida, this is a practical planning consideration — PDT is typically scheduled for days when patients can remain predominantly indoors afterward.
Frequently asked questions
Is PDT painful?
During the light exposure phase, most patients experience a burning, stinging, or heat sensation of varying intensity. The discomfort is managed with cooling measures during the session and typically resolves within a few hours of light exposure ending. Some patients tolerate it easily; others find it significantly uncomfortable. We prepare patients for the range of possible experiences.
How many treatments will I need?
Many patients see substantial AK clearance after a single treatment. Patients with extensive sun damage across large surface areas often benefit from a second session. We assess the response after the skin has healed from the first treatment and discuss whether a second course is warranted.
What’s the difference between PDT and laser treatment?
Laser treatments use focused energy to resurface or ablate tissue through thermal mechanisms. PDT uses blue fluorescent light to activate a photosensitizing chemical agent. They are completely different mechanisms of action, different procedures, and suited to different clinical problems. PDT is specifically indicated for actinic keratoses and the field of sun-damaged skin around them.
Can PDT be used anywhere on the body?
It’s most commonly used on the face, scalp, and forearms — the areas with the highest density of actinic damage in most patients. It can be used in other locations but is less commonly indicated elsewhere.