A topical nanoemulsion-based gel formulation containing 5-aminolevulinic acid (ALA), a metabolic precursor of the photosensitizer protoporphyrin IX, with a potential application for enhanced photodynamic therapy (PDT) for various precancerous and malignant skin lesions. After topical administration of a thick layer of the ALA-based BF-200 gel formulation to the affected area, ALA penetrates the skin and is intracellularly converted to protoporphyrin IX (PpIX). Exposure of PpIX to the proper excitation wavelength of light generates singlet oxygen molecules, resulting in a local cytotoxic effect.