EU Guideline Method for UVA In Vitro Determination

This method provides two metrics describing the UVA protection of a sunscreen. Firstly, the method provides in vitro UVA protection factors (UVA-PF) which have been shown to correlate well with in vivo UVA-PF values derived from the PPD method (the latter being considered as the in vivo reference). Secondly, the method also provides a means of calculating Critical Wavelength values.

The test is based on an assessment of the UV transmittance of a thin film of sun-screen sample spread on a roughened substrate after exposure to a controlled dose of UV radiation from a defined UV source. Due to the current lack of inter-laboratory reproducibility of absolute in vitro UV measurements, each set of sunscreen trans-mission data is adjusted by first converting to absorption data (before and after UV exposure) and then by multiplying by a correction coefficient. This coefficient is de-termined iteratively from the non-exposed sample‟s absorbance data to provide a calculated in vitro SPF value equal to the labelled (in vivo) SPF.

The sunscreen sample is exposed to an irradiation dose proportional to an initial UVA protection factor UVAPF0, calculated from the corrected absorbance data of the non-exposed sample.

Both the final in vitro UVA-PF and in vitro Critical Wavelength value, c, are calcu-lated from the absorbance data of the UV exposed sample.

Procedures

In vitro transmission measurement of the sunscreen product spread on a PMMA plate, prior to UV irradiation. Acquisition of initial UV spectrum with A0 data.

Mathematical adjustment of the initial UV spectrum using coefficient “C” to achieve an in vitro SPF (0% UV dose) equal to the labelled SPF (in vivo). UVAPF0 is calculated using A0 and C.

A single UV dose D is calculated, proportional to UVAPF0.

UV exposure of the same sample as in step 1, according to the calculated UV dose D.

In vitro transmission measurement of the sunscreen product after UV ex-posure. Acquisition of second UV spectrum with A data.

Mathematical adjustment of the second spectrum (following UV exposure) according to the same C coefficient, previously determined in step 2. Cal-culation of the in vitro UVA protection factor UVA-PF after irradiation using A and C and calculation of the Critical Wavelength value from A data.