“…The kynurenine pathway is expressed at regulated levels in all skin cells and, in connection with the N -methyl- d -aspartate (NMDA) receptor, is responsible for cellular proliferation, differentiation, migration and, ultimately, skin barrier function. In the skin and eyes of humans, kynurenine and its derivatives act as UV-A and VL absorbers, immunomodulators, and markers of oxidative distress. − The redox-active UV-A/HEVR-absorbing products of Trp oxidation, such as anthranilic acid, xanthurenic acid, melatonin, 5-methoxytryptamine and 5-methoxytryptophol, quinolinic acid, and picolinic acid, , play multiple roles in metabolism and have been implicated in pathological conditions such as dementia . The Kyn pathway is required for the biosynthesis of NAD + , a central coenzyme in metabolism that is key for DNA repair under ionizing radiation …”