Vasanop VachiramonChaninan KositkuljornKanchana LeerunyakulKumutnart ChanprapaphFaculty of Medicine, Ramathibodi Hospital, Mahidol University2020-08-252020-08-252020-01-01Journal of Cosmetic Dermatology. (2020)14732165147321302-s2.0-85088942695https://repository.li.mahidol.ac.th/handle/20.500.14594/58223© 2020 Wiley Periodicals LLC Background: Isobutylamido thiazolyl resorcinol (ITR, Thiamidol®) has been proposed as a potent tyrosinase inhibitor. A formulation containing ITR has recently shown promising efficacy for the treatment of some hyperpigmentary conditions. Objectives: This study aimed to evaluate the efficacy and safety of ITR in the prevention of ultraviolet (UV)-induced hyperpigmentation in human skin. Materials and Methods: We performed a randomized, single-blinded, pilot study in 30 healthy participants. One arm was randomly assigned to receive an ITR-containing product for three weeks. Three hyperpigmented spots were induced by UVB irradiation on both arms after 3 weeks of ITR application. Outcome evaluations included measuring mean lightness index (*L) obtained by colorimeter, hyperpigmentation scores by visual analog scale (VAS), and adverse effects. Results: Both experimental sides showed no significant difference in terms of skin lightening after ITR application. However, the ITR-treated sides showed a statistically significant lower mean lightness index compared to control after an induction with UVB. In addition, the ITR-treated sides had an earlier improvement and resumed the normal skin color after 3 weeks post-UVB induction. A clinical evaluation by a blinded nontreating physician and subjects was more favorable on the ITR-treated side than the control side (P <.05). No significant side effect was noted. Conclusions: ITR is an effective agent in the prevention of pigmentary change from UVB irradiation and may serve as a promising agent for preventing other hyperpigmentary conditions.Mahidol UniversityMedicineArticleSCOPUS10.1111/jocd.13615