**4.7 Photodynamic therapy**

Photodynamic therapy (PDT) with topical 5-aminolevulinic acid has a good curative effect, especially in recalcitrant facial flat warts [20–22]. It is unclear, but selective photothermolysis of oxyhaemoglobin within the dilated microvasculature of the warts leads to destruction of capillaries followed by improvement of warts, may be the mechanism of action of this curative effect [23]. Many factors affect the efficacy of PDT, including photosensitizer concentration; solvent type; incubation time; type, dose, and time of irradiation of the light; and the area of exposed parts. ALA gel (10%) was applied topically to lesions and incubated for 3 h. The lesions were irradiated by an LED light of 630 ± 10 nm at dose levels of 60–100 mW/cm**.** At the 24-week follow-up, the average effective rate was 88.8%, with no recurrences. No significant side effects were reported [24].
