The British journal of dermatology
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Photodynamic therapy (PDT) is based on the combination of an exogenously administered precursor of photosensitizer [protoporphyrin IX (PpIX)] synthesis and exposure to light. Choosing the optimal wavelength is important. Red light penetrates deeper into tissue, while violet light is more efficient in activating PpIX but does not penetrate so deeply. ⋯ Topical ALA-PDT with violet light allows longer exposure times before pain is induced and gives less erythema as compared with topical ALA-PDT with red light.