A novel proposal for the assessment of sunscreen product efficacy against UVA

The ideal characteristics are outlined for an assessment method for the protective properties of sunscreen products against UVA. Existing sun protection factors (SPFs) are reliant on largely UVB-induced delayed erythema, which is inappropriate for the UVA. A novel instrumental method for assessing a protection index is detailed which is applicable to the UVA. The validation of the method relies on measurements in the UVB and comparison with conventional SPFs, since no reliable UVA protection index exists. The method uses UV transparent skin casts to which products can be applied. Throughput of appropriately filtered light, with and without applied product, is measured to generate a protection index. Comparison with SPFs confirms that the measurements are similar to those generated by in vivo methods, but that careful choice of the casting medium is essential.