 Photofrin is a sensitizer used in photodynamic therapy, PDT, to treat cancer and skin diseases. Since its approval in the 1990s, various dye sensitizers have been developed, with porphyrinid derivatives being the most successful in producing requisite singlet oxygen. Other porphyrinid compounds approved by US FDA include benzo-porphyrin derivative monoacid ring A, BPDMA, metatetra, hydroxyphenol, chlorine, and THPC, enospartylchlorine E6, and PE6, and precursors to endogenous protoporphyrin 9, PPIX1, 5-aminolevelynic acid, ALA, methylamenolevelynate, ML, hexamenolevelynate, HAL. While no non-porphyrin sensitizer has been approved for PDT applications, entroquinone, phenothizine, xanthine, cyanine, and curcuminid sensitizers are under consideration and some are being evaluated in clinical trials. This article was authored by Harold S. Freeman and Alexander B. Ormond. We are article.tv, links in the description below.