Photodynamic Therapy: Overview and Mechanism of Action.

Abstract

Photodynamic therapy (PDT) is a versatile treatment with diverse applications in dermatology. PDT combines photosensitizers, most commonly 5-aminolevulinic acid (ALA) or methyl aminolevulinate (MAL), and a light source, such as light-emitting diodes (LEDs), fluorescent bulbs, lasers, flash lamps, or sunlight, in the presence of molecular oxygen to induce therapeutic effects primarily through singlet oxygen and reactive oxygen species generation. Downstream cellular and physiological effects include apoptosis, necrosis, and immune modulation. PDT efficacy depends on photosensitizer parameters, including photosensitizer type, concentration, dosing, temperature, and incubation time, and light source parameters such as light source, power density, wavelength, and fluence. PDT is generally safe and well tolerated; potential adverse effects such as pain and erythema are typically mild and self-limiting. Part I of this Continuing Medical Education (CME) provides a foundational overview of PDT principles, including mechanisms of action, photosensitizers, and light sources.