Spectral monitoring of photoirradiated skin lipids: MS and IR approaches

An investigation of the effects of UVA irradiation on the stratum corneum lipids was carried out in vitro on films. The modifications of their conformational order were studied by FTIR and the formation of new entities was detected by mass spectroscopy.The results show not only differences in behaviour of the three lipid classes (fatty acids (FA), ceramides (CER), and cholesterol), but also variation within a class, depending on the molecules structure. Upon UVA irradiation, β scission occurs on all the components, saturated and unsaturated. Moreover, unsaturated FA or CER having a double bond on their FA moiety may become saturated or may be transformed into their free radical form. Unsaturated FA are more sensitive to UVA and lead more easily to oxygenated components than unsaturated CER. The chemical effects are irradiation dose dependent but do not deeply influence the supramolecular organisation of these lipids. The global conformation of the lipids stays in an orthorhombic state, a decrease of the packing density however is observed.