SUN CARE 31
optimized dispersion techniques and controlled processing conditions to preserve particle stability and performance in the final sunscreen product.
Biologically active ingredients Certain anti-inflammatory, antioxidant, or skin- soothing ingredients can influence the outcome of human SPF testing by attenuating the skin’s erythemal response to UV exposure, even though these ingredients do not directly absorb, reflect, or scatter UV radiation. UV irradiation triggers inflammatory responses, including the release of pro-inflammatory mediators that lead to erythema. Ingredients such as dipotassium glycyrrhizate, bisabolol, and tocopheryl acetate have been shown to inhibit inflammatory signaling pathways and/or neutralize free radicals, thereby reducing the intensity of visible erythema induced by a given UV dose. In standardized human SPF test methods, such as ISO 24444, the measured endpoint is the minimal erythemal dose (MED). When an active ingredient within a formulation suppresses erythema development, a higher UV dose is required to reach this endpoint, resulting in a higher calculated SPF value. This effect represents a SPF ‘boost’ mediated
through biological modulation rather than through conventional physical or chemical UV-filtering mechanisms. Importantly, this pathway should be recognized as a complementary skin-protective benefit, distinct from direct UV attenuation.
Photo stabilizers Many organic UV absorbers, particularly broad-spectrum UVA filters, are susceptible to photodegradation upon prolonged exposure. Such degradation results in a progressive loss of photoprotective efficacy and may lead to the formation of degradation products that have the potential to cause skin irritation. Photo stabilizers function by preferentially
absorbing or quenching excited-state energy, thereby protecting UV filters from photochemical decomposition and preserving their molecular integrity during exposure.5 AVB is a well-known example of a photo
unstable UVA filter. However, it can form highly effective and photostable systems when combined
TABLE 3: IN VITRO SPF VALUE OF TWO FORMULAS, ONE CONTAINING 3% AB OIL WHILE THE OTHER CONTAINING 3% BHB UL
Formula SPF AB oil 35.83 3% BHB UL 45.17
with certain co-filters that also exhibit stabilizing properties, such as octocrylene (OCT), ethylhexyl triazone (T150), and bis-ethylhexyloxyphenol methoxyphenyl triazine (BEMT). A study was conducted to monitor the
photodegradation of AVB in simple solution systems under simulated solar irradiation when combined with various co-filters. The percentage of AVB remaining after UV exposure was quantified for each filter combination. The results demonstrate that the inclusion of
specific, well-selected photo stabilizers — many of which also function as UV filters — is essential for preserving AVB’s integrity during UV exposure. Effective photo stabilization, is therefore critical to maintaining the labelled SPF and UVA protection factor (UVA-PF) throughout product use, while simultaneously supporting the overall safety profile of the formulation.
Conclusion The development of next-generation sunscreen products represents a multidisciplinary exercise in synergistic formulation science. As demonstrated throughout this work, achieving high, stable, and broad-spectrum photoprotection goes far beyond the selection of conventional UV filters alone. The strategic integration of SPF synergistic
agents — through mechanisms such as film formation, optimized solubilization and dispersion, controlled light scattering, biological modulation, and effective photo stabilization — enables formulators to enhance sunscreen performance beyond simple additive effects.5 The experimental data presented for agents
like Aegivita BHB UL and Aegivita PS-15 illustrate how targeted booster technologies can address specific formulation challenges, ranging from the stabilization of photolabile UV filters to promoting uniform and durable skin coverage.
TABLE 4: IN VITRO SPF AND PFA VALUE OF DIFFERENT FORMULAS CONTAINING DIFFERENT PARTICLE SIZES OF MBBT DISPERSION
Sample 1#
2# 3#
Particle size (DN50) ˜100nm
˜200nm ˜400nm
SPF
48.44 44.93 34.03
PFA
8.85 8.64 6.68
These examples highlight the critical role of
formulation design in translating molecular and physicochemical principles into measurable improvements in SPF and broad-spectrum protection. In conclusion, a comprehensive understanding
and deliberate application of SPF synergistic strategies are essential for developing of modern sunscreens that combine high efficacy, formulation stability, and favourable sensorial attributes. Continued innovation in this field is expected to further refine these synergistic interactions, advancing the boundaries of photoprotection to meet evolving regulatory standards and consumer expectations.
References 1. Nitulescu G, Lupuliasa D, Adam-Dima I, Nitulescu GM. Ultraviolet Filters for Cosmetic Applications. Cosmetics. 2023; 10, 101
2. Chen Y, Xu H, Liu Y, Fu Q, Zhang P, Zhou J, Dong H, Yan X. Structural Similarity-Induced Inter- Component Interaction in Silicone Polymer- Based Composite Sunscreen Film for Enhanced UV Protection. Polymers. 2024; 16, 3317
3. Sohn M, Amorós-Galicia L, Krus S, Martin K, Herzog B. Effect of emollients on UV filter absorbance and sunscreen efficiency. Journal of Photochemistry and Photobiology B: Biology. 2020; Volume 205, 111818,ISSN 1011-1344
4. Herzog B, Quass K, Schmidt E, Mueller S, Luther H. Physical properties of organic particulate UV absorbers used in sunscreens: II. UV-attenuating efficiency as function of particle size. Journal of Colloid and Interface Science. 2004; volume 276, issue 2, pages 354-363
5. Lhiaubet-Vallet V, Marin M, Jimenez O et al. Filter-filter interactions. Photostabilization, triplet quenching and reactivity with singlet oxygen. Photochem Photobiol Sci. 2010; 9, 552–558
% UV Recovery ■ % AVB Recovery ■ AVB+APlus
PCM
AVB+OCT
AVB+BEMT
AVB+OMC 0 20 40 Figure 3: Percentage recovery of UV filters after four hours of irradiation
www.personalcaremagazine.com June 2026 PERSONAL CARE MAGAZINE 60 80 100
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