ABSTRACT
Terrestrial solar ultraviolet radiation (UVR) is a major environmental hazard and is the cause of the majorityofskincancers,especiallyinsun-sensitivewhite-skinnedpeople.§ereisconsiderableevidencethatnonmelanomaskincancersareduetoUVR-inducedDNAdamage(Ziegleretal.,1994). UVRalsocausesphotoaging.§ee¨ectsofUVRontheskin,whetheracutesuchassunburnorlong term,arecausedbydamagetotargetmolecules.§iscanbedoneintwoways:(1)Directabsorption ofUVRbythetargetmoleculesuchasDNAorurocanicacid.Insuchcases,thetargetmoleculeisthe chromophore.OneofthemostimportanttypesofDNAdamageformedinthiswayisthecyclobutane pyrimidinedimer(CPD),whichhasbeenimplicatedinerythema,immunosuppression,mutagenesis, andskincancer(Yarosh,2004).Alternatively(2)thetargetmoleculecanbedamagedindirectlywhen UVRisabsorbedbyanotherchromophore,whichgeneratesreactiveoxygenspecies(ROS),suchas thesuperoxideanion,hydrogenperoxide,thehydroxylradical,andsingletoxygen.ROScaninteract withcellularproteins,membranes,andDNAtoaltertheirfunctions.Consequently,excessiveROSmay arrestthecellgrowthcycleandcauseinÀammation,immunosuppression,skinaging,DNAdamage (Cadet et al., 2009), mutation, and cancer.
