Keurentjes AJ, Jakasa I, van Dijk A, et al. - In the present study, the researchers established a dose-response relationship for Stratum corneum (SC) biomarkers and explored their suitability for in vivo assessment of the blocking effect of two sunscreens with a high sun protection factor (SPF) (50+). Twelve participants were exposed to a broad-spectrum UVB (280-320 nm), five times a week, during one week. Cis-urocanic acid is a sensitive, non-invasive marker of the internal UVR dose that allows for in vivo evaluation of the blocking effect of high SPF sunscreens in the UVB-region. Immunological SC markers have low sensitivity in detecting immune response at sub-erythemal UVR dosages, implying that they may be useful only at higher and/or repeated UVR exposure.