Light Source Spectrum Strongly Influences the In Vitro Estimation of Sun Protection Factor

Abstract

Irradiation from an artificial solar simulator that matches the relative cumulative erythema effectiveness (RCEE) of sunlight is used for in vivo sun protection factor (SPF) testing, whereas irradiation that matches the spectrum of natural sunlight (NS) is generally used for in vitro SPF testing. This study was designed to clarify whether this difference is important. Eight sunscreens spread on artificial substrates and several optical filters as sunscreen mimics were used. Their in vitro SPF values were evaluated using RCEE-compliant and NS spectrum-matching light sources in calculation. The calculated in vitro SPF values obtained using NS light (SPF [NS]) were lower than those obtained using RCEE light (SPF [RCEE]). The in vitro SPF (RCEE) values showed a better correlation and better agreement with in vivo SPF values, as compared with the in vitro SPF (NS) values. A marked difference between in vitro SPF values obtained with the two light sources in calculation was found for sunscreens showing low transmittance in the ultraviolet B region. To obtain in vitro SPF values that correspond well to in vivo SPF values measured with currently accepted methodology, it is important to use an RCEE-compliant light source.

New approach for a reliable in vitro sun protection factor method Part I: Principle and mathematical aspects

“…The spectral erythemal effectiveness values of the source spectrum are then integrated from 290 nm to the various successive reference wavelength values in order to produce the cumulative erythemal effectiveness for each spectral waveband, and the total erythemal effectiveness is calculated up to 400 nm. Thus, to ensure reliable results, the following UV source specifications are used :…”

Validation of an in vitro sun protection factor (SPF) method in blinded ring‐testing

“…Various efforts to develop in vitro SPF test methods have resulted in a variety of potential approaches, all united by the combined use of a UVR‐transparent substrate (which acts as a skin analogue and upon which product is spread) and a UVR spectrophotometer (to measure transmitted UVR) . In the in vitro sun protection methods groups of COLIPA/CE, coherent programmes to develop such methods have been underway since 2008, building upon the procedures developed in the COLIPA in vitro UVA method (now ISO24443).…”

“…Whereas the COLIPA in vitro UVA method used an index vs. the SPF value measured in vivo to correct the amplitude of the in vitro UVAPF value , there is (by nature) no such correction that can be applied in an in vitro SPF method. Considerable effort, therefore, has been given to the development of, for example, optimal UVR‐transparent substrates, irradiation protocols/parameters and automated spreading procedures to enable the in vitro prediction of in vivo SPF with accuracy, repeatability and reproducibility .…”

The Influence of Short-Wave and Long-Wave Radiation Spectrum on the Photostability of Sunscreens

“…Here, the Multiport solar simulator by Solarlight is the device of choice equipped with a xenon lamp and the filters WG320 and UG11 to eliminate wavelength below 300 nm and above 400 nm. Since the measured final SPF takes the photostability of a sunscreen into account, SPF testing under non-real-time conditions overestimates the SPF when it comes to non-photostable samples [27]. Currently this problem particularly exists in the attempt to achieve a high correlation between SPF in vivo and SPF in vitro values [27], which is needed to replace the International Standard EN ISO 24444: 2010 by an alternative method.…”