30 SUN CARE
efficacy is highly dependent on the complete solubilization of UV filters within the oil phase and their uniform dispersion at the molecular level, which enables efficient absorption of ultraviolet radiation. Certain oils function not only as passive solvents but also as effective co-solvents, markedly increasing the solubility of specific organic UV filters.3 For example, Butyloctyl Salicylate (BHB UL) has been shown to exhibit strong solvating capability for a range of commonly used organic UV filters, thereby facilitating improved molecular dispersion and contributing to enhanced SPF performance. Solubility studies demonstrate that BHB
UL exhibits substantially higher solubilization capacity for UV filters such as AVB (Avobenzone, INCI: butyl methoxydibenzoylmethane), S (INCI:Bis-Ethylhexyloxyphenol Methoxyphenyl Triazine), and APLUS (INCI: Diethylamino Hydroxybenzoyl Hexyl Benzoate) , compared to conventional emollient oils (e.g., C12- 15 Alkyl Benzoate). This enhanced solubility enables the
formulation of sunscreen systems with higher UV filter loadings while maintaining formulation stability. Storage stability testing indicates that BHB
UL functions as an effective co-solvent within the formulation. Compared with the formulation containing only AB oil (a), the formulation incorporating both AB oil and BHB UL (b) exhibited improved stability over the storage period, suggesting enhanced resistance to phase separation of UV filters. For inorganic (mineral) UV filters such as titanium dioxide and zinc oxide, formulation efficacy is primarily governed by the prevention of particle agglomeration, which is essential for achieving uniform skin coverage and forming an effective physical UV barrier. Oils possessing superior spreading and dispersing characteristics contribute to maintaining stable particle dispersion within the formulation and facilitate homogeneous distribution upon application. A broad-spectrum sunscreen formulation
incorporating multiple UV filters was prepared using BHB UL, and its in vitro SPF was evaluated in comparison with a control formulation containing conventional solvents (AB oil). The formulation containing the synergistic
agent exhibited a SPF increase of approximately 20% relative to the control, indicating enhanced photoprotective performance. These results confirm that optimization of UV filter dissolution and dispersion plays a fundamental role in improving overall sunscreen efficacy.
Light scattering The photoprotective efficacy of inorganic UV filters and certain surface-treated particulate organic filters, such as methylene bis-benzotriazolyl tetramethylbutylphenol (MBBT), is partially derived from their ability to scatter incident UV radiation. Light scattering effectively increases the optical
path length of UV radiation within the sunscreen film, thereby enhancing the probability of its
PERSONAL CARE MAGAZINE June 2026
Figure 1: (a) AVB dissolved in AB oil without BHB UL, and (b)AVB dissolved in AB oil with BHB UL. Photos were taken after AVB dissolved at 85°C and left to stand at room temperature for three days
C D
TABLE 2: SOLUBILITY OF SELECTED UV FILTERS IN BHB UL AND C12-15 ALKYL BENZOATE AVB
Soulte (g) Solvent BHB UL C12-15 ALKYL BENZOATE (AB OIL) A 13% 8% B S 26% 6%
A Plus 40% 6%
E
F
Figure 2: A titanium dioxide dispersion prepared using BHB UL remains stable with minimal settling and forms an uniform layer when applied, whereas a control using a common cosmetic oil shows significant, unevenly dispersed particles. (c) TiO2 in BHB UL
in AB oil, (d) TiO2
absorption by the complementary UV filters present in the formulation. Scattering efficiency is strongly dependent on particle size and distribution.4
From a theoretical
perspective, maximum scattering at a given wavelength occurs when the particle diameter is approximately half of that wavelength. This necessitates precise control of particle size in the submicron to nanometer range for effective UV scattering. To investigate this effect, the SPF contribution
of aqueous dispersions of MBBT coated with decyl glucoside (MD) with different particle size distributions was evaluated. These dispersions were incorporated at identical concentrations into final
sunscreen formulations. In vitro SPF measurements revealed that
MD dispersion with a narrower particle size distribution and an average particle diameter closer to the optimal scattering dimension produced a significantly greater SPF enhancement than dispersion with larger mean particle sizes or broader size distributions. These findings clearly demonstrate that maximizing light-scattering efficiency through precise control of particle size — either of the synergistic agent or the particulate UV filter itself — can substantially enhance SPF without increasing the overall concentration of UV absorbers. This approach underscores the importance of
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in BHB UL, (e) ZnO in AB oil, (f) ZnO
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