**3.8 Iontophoresis**

Iontophoresis is a method based on the use of a voltage gradient applied to an electrolytic formulation, using both a positive (anode) and negative (cathode) electrodes on skin to improve transdermal drug delivery [50]. The advantages of iontophoresis are that it is a non-invasive technique that preserves the skin intact, providing controlled and targeted delivery of the drug. However, regarding PDT, special attention should be taken to ensure that the photosensitizing drug does not enter the systemic circulation, which can cause unexpected side effects [51].

This technique has a potential to decrease the DLI since *ex vivo* experiments demonstrated PpIX accumulation in human SC were achieved faster compared with topical application only [51]. In addition, studies with patients proved that the use of iontophoresis in clinical protocols is an effective method and reduces the incubation time by 1 h [52].
