The Effects of Solvents on Sunscreens: A New Ester to Improve Efficiency

Jun 1, 2011 | Contact Author | By: Thomas O’Lenick, PhD, SurfaTech Corp.; and Dennis Lott, Lott Research Inc.
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Title: The Effects of Solvents on Sunscreens: A New Ester to Improve Efficiency
sorbeth 2 hexaoleatex SPFx solventx sunscreen activesx
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Keywords: sorbeth 2 hexaoleate | SPF | solvent | sunscreen actives

Abstract: The present paper evaluates the effects of solvent systems on the in vivo SPFs of sunscreen formulations. Formulations incorporating identical active systems were prepared using traditional solvent systems and varying concentrations of sorbeth 2 hexaoleate, a new ester having both polar and nonpolar segments. Results indicate the ester enhances SPF in a dose-dependent manner.

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T O'Lenick and D Lott, The Effects of Solvents on Sunscreens: A New Ester to Improve Efficiency, Cosm & Toil

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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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Table 1. Tested sunscreen formulations

Table 1. Tested sunscreen formulations

To evaluate the effects of solvents on the SPF values of sunscreens, a series of formulas (see Table 1) was prepared and their SPFs tested on the same subjects.

Table 2. SPF test results for formulas 1–13 in Table 1

The SPF test results for formulas 1–13 are shown in Table 2.

The SPF test results for formulas 1–13 are shown in Table 2.

Figure 1. Absorbency of commonly used organic sunscreens

Figure 1. Absorbency of commonly used organic sunscreens

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.

Figure 2. Sorbeth 2 hexaoleate esters are characterized as having hydrophilic arms covalently bonded to a hydrophobic end group

Figure 2. Sorbeth 2 hexaoleate esters are characterized as having hydrophilic arms covalently bonded to a hydrophobic end group

These compounds contain hydrophilic arms covalently bonded to a hydrophobic end group (see Figure 2), and this difference in polarity makes them soluble and effective when added into polar oil-based sun care formulations, as will be shown.

Figure 3. Results of SPFs obtained from Formulas 8, 9 and 10

Figure 3. Results of SPFs obtained from Formulas 8, 9 and 10

Figure 3 graphically displays the SPF results for Formulas 8, 9 and 10, and these results suggest a linear relationship between increasing amounts of sorbeth 2 hexaoleate and SPF.

Figure 4. Results of SPFs obtained from Formulas 11, 12 and 13

Figure 4. Results of SPFs obtained from Formulas 11, 12 and 13

Figure 4, showing the SPFs for Formulas 11, 12 and 13, suggests that with more sunscreen actives, the SPF increases with increased sorbeth 2 hexaoleate.

Footnotes (CT1106 O'Lenick)

a The Spider Ester product (INCI: Sorbeth 2 hexaoleate) is manufactured by SurfaTech Corp.
b The Solar Light Model 15S Xenon Arc. Solar Simulator Lamp is manufactured by Solar Light.

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