Due to a rise in melanoma and other skin related diseases,1–3 protecting the skin from the deleterious effects of the sun has become a priority in recent years. The quest for complete protection from the sun has led numerous research efforts for not only effective sunscreens, but also products that are extremely efficient in providing higher SPFs with lower levels of UV filters.4 The effectiveness of sunscreen products is typically denoted in terms of sun protection factor (SPF) and this value can be altered in a variety of ways including the specific sunscreen agents chosen or the type of delivery system or formula employed.
Sunscreen products work based on the ability of sunscreen actives to absorb photons in the UVB and UVA range. Simply put, according to Beer’s Law5, 6 the absorbance of light passing through a liquid is directly related to the concentration of the absorbing material in the liquid. However, considering the absorbance levels for US-approved sunscreen actives (see Figure 1), one can readily deduce that the actives must be utilized at many times more than would be expected in order to obtain the desired SPF.6 This difference can be attributed to several factors such as application uniformity,7, 8 complete UVB and UVA spectra coverage,9 formulation photostability10 and formulation polarity;11 in addition, one crucial factor is the solvent system used in the sunscreen formulation.12, 13
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