“…For skin treatments, 5-aminolevulinic acid (5-ALA), which is converted into the endogenous PS protoporphyrin IX (PpIX), has an absorption maximum at 630 nm and is widely used [22,26,27]. Methylene blue (MB) is a well-known phenothiazine derivative with great importance in medicine, including antimicrobial and antiviral light-induced activity [25,28,29]. The third PS generation corresponds to enhanced forms of the first and second generations.…”