In vitro testing to assess the UVA protection performance of sun care products

Abstract

The UVA protection delivered by sunscreens is an issue of increasing importance due to the increasing knowledge about UVA-induced skin damage. In Europe there is no officially accepted method available to determine the degree of UVA protection. Therefore, the objective of the present study was to design a protocol combining the merits of an in vitro model, which are simple and reproducible, with aspects known to be relevant from in vivo studies. The principle is: an UV-transparent support to which the test product is applied, a (pre)irradiation and a transmission measurement. Transpore(R) tape (standard support for SPF determinations) was found to be incompatible with many preparations on prolonged contact times. Roughened quartz was adopted as a suitable alternative. Transmission measurements on this support are not reliable with a layer of 2 mg cm(-2) (standard for SPF) due to detection limitations of spectrophotometers, hence a reduced layer of 0.75 mg cm(-2) was adopted. Overall, it is very difficult to apply products in a reproducible thin layer on appropriate substrates. As a consequence, absolute parameters derived from the transmission profile show relatively large dispersion, whereas relative parameters, such as critical wavelength lambda(c)[1] or UVA/UVB ratio are much less sensitive to unavoidable variations in layer thickness. An increase in deviations was observed when the samples were irradiated before measurement. It is crucial to control the output carefully (spectral distribution and even more importantly, irradiance and dose delivered) of the light source. By doing so and also taking into account the previous learning steps, a protocol was drafted and tested in a ringtest (four samples in six laboratories). The results are encouraging and show that if relative parameters (e.g. lambda(c), UVA/UVB ratio) are considered, the intra- as well as interlaboratory reproducibility is clearly better than can be obtained in vivo. In general, we describe a suitable method, which can be considered in any future official discussions about the methodology to determine UVA protection.

Problems of in vitro SPF Measurements Brought about by Viscous Fingering Generated during Sunscreen Applications

“…This method requires the process of irradiation of UV light on a human's back as a test subject. Challenges thus have been made to develop an in vitro SPF measurement method [2,3,4,5,6,7,8,9], since it gives results more quickly, is less expensive and is more ethical. For an in vitro SPF measurement, the recommended amount of sunscreens is applied on a standard substrate to prepare the sample.…”

Sunscreen tests: Correspondence between in vitro data and values reported by the manufacturers

“…Studies performed using Excised Human Stratum Corneum and Excised Human Epidermis have been reported, but the biological nature of these materials introduces practical problems. The choice of the substrate is a very critical issue as sunscreen tests performed on different substrates are not always reproducible [4][5][6], especially when the substrate/sunscreen is irradiated before or during the tests. Moreover, when a particular substrate is used other parameters can affect the final in vitro SPF value.…”

Utilization of Salmon Milt DNA Against UV Damage

“…The UVA/UVB ratio and critical wavelength are important parameters to evaluate the UVA protection ability for human skin of a UV protector; the UVA/UVB ratio is defined as the ratio of the means of absorbances from UVA and UVB, and the critical wavelength is the point where 90% of the area under the curve lies, starting at the UVB end (290 nm) [33]. Table 2 lists the calculated UVA/UVB ratios and critical wavelengths of salmon milt DNA with or without UVC irradiation.…”