Gniadecki, R, et al. “Variable Expression of Apoptotic Phenotype in Keratinocytes Treated With Ultraviolet Radiation;Ceramide;Or Suspended in Semisolid Methylcellulose”. Acta Dermato-Venereologica, vol. 78, no. 4, Aug. 1998, pp. 248-57, doi:10.1080/000155598441800.