In vitro assessment of the broad-spectrum ultraviolet protection of sunscreen products  Brian L. Diffey, DSca, Paul R. Tanner, BSb, Paul J. Matts, PhDc, J.Frank Nash, PhDb  Journal of the American Academy of Dermatology  Volume 43, Issue 6, Pages 1024-1035 (December 2000) DOI: 10.1067/mjd.2000.109291 Copyright © 2000 American Academy of Dermatology, Inc Terms and Conditions

Fig. 1 Absorption spectrum for hypothetical sunscreen product. UV attenuation is determined at fixed intervals across UV spectrum using substrate spectrophotometry. Wavelength below which 90% of the area under the whole absorption spectrum from 290 to 400 nm falls is the critical wavelength. The shape of the absorption spectrum is independent of application density. Journal of the American Academy of Dermatology 2000 43, 1024-1035DOI: (10.1067/mjd.2000.109291) Copyright © 2000 American Academy of Dermatology, Inc Terms and Conditions

Fig. 2 Absorption spectra for UVB (A) and broad-spectrum (B) sunscreen products. Shaded areas represent 90% of the area under the absorption curves from 290 to 400 nm. The critical wavelength is the singular point below which 90% of the whole absorption spectrum falls. Journal of the American Academy of Dermatology 2000 43, 1024-1035DOI: (10.1067/mjd.2000.109291) Copyright © 2000 American Academy of Dermatology, Inc Terms and Conditions

Fig. 3 Relationship between labeled SPF and critical wavelength for 59 commercially available products. Journal of the American Academy of Dermatology 2000 43, 1024-1035DOI: (10.1067/mjd.2000.109291) Copyright © 2000 American Academy of Dermatology, Inc Terms and Conditions

Table III Absorption bands and critical wavelength for the most commonly used UV filters Journal of the American Academy of Dermatology 2000 43, 1024-1035DOI: (10.1067/mjd.2000.109291) Copyright © 2000 American Academy of Dermatology, Inc Terms and Conditions

Fig. 4 Absorption spectrum and critical wavelength for 1.5% PBSA (critical wavelength = 324 nm), 3% AVO (critical wavelength = 383 nm), and their combination (critical wavelength = 378 nm). PBSA, AVO, and their combination were prepared as oil-in-water emulsions and the absorption spectrum determined by means of substrate spectrophotometry. PBSA has the lowest critical wavelength and AVO the highest. The UV filters alone and in combination have broad absorption spectra. Journal of the American Academy of Dermatology 2000 43, 1024-1035DOI: (10.1067/mjd.2000.109291) Copyright © 2000 American Academy of Dermatology, Inc Terms and Conditions

Fig. 5 Photostability of model sunscreen products after increasing doses of solar simulated UV. Each product was exposed to 0, 10, 20, or 30 J/cm2 solar simulated radiation. Each value is the mean of 5 independent samples. The critical wavelength was calculated from the absorption spectrum obtained by means of substrate spectrophotometry. Journal of the American Academy of Dermatology 2000 43, 1024-1035DOI: (10.1067/mjd.2000.109291) Copyright © 2000 American Academy of Dermatology, Inc Terms and Conditions

Fig. 6 Relationship between phototoxic protection factor and critical wavelength. Journal of the American Academy of Dermatology 2000 43, 1024-1035DOI: (10.1067/mjd.2000.109291) Copyright © 2000 American Academy of Dermatology, Inc Terms and Conditions