Several traditionally used organic UV filters, such as Octocrylene, are faced with rising concerns regarding their environmental and health safety profiles. Emollients directly influence the possibility to formulate with safe, highly efficient alternatives. In their function as solubilisers of solid organic UV filters, emollients determine the maximum applicable UV filter concentration and resulting SPF. Emollients also have an impact on dispersion stability of inorganic UV filters such as Zinc Oxide and Titanium Dioxide. Furthermore, they strongly influence skin feel and homogeneous product application, thus supporting efficient skin protection and consumer acceptance.
Jungbunzlauer offers two emollients specifically suited for sunscreen formulation. CITROFOL® AI (Triethyl Citrate) and CITROFOL® BI (Tributyl Citrate) are clear, odourless, oily liquids and have a long history of safe use in personal care products. Highlighting their applicability in sun protection, important parameters comprising solvent power, influence on sun protection factor (SPF) and UVA protection factor (UVA-PF), dispersability of inorganic filters and sensory attributes were investigated.
Our solubility tests revealed the exceptional solvent power of CITROFOL® BI for the UV filter Ethylhexyl Triazone (EHT) of up to 35%. Both CITROFOL® BI and CITROFOL® AI showed excellent solvent power of 29% for Diethylamino Hydroxybenzoyl Hexyl Benzoate (DHHB). Greater solvent power of the emollient allows for higher filter loading and thus higher SPF. It also increases formulators’ flexibility regarding the exact composition of the oil phase: the overall amount of oil can be lowered and co-emollients can be chosen based on their sensory performance.
A sensory profiling of Jungbunzlauer’s CITROFOL® citrate esters in test emulsions showed that CITROFOL® BI was rated similar to the reference with C12-15 Alkyl Benzoate and can thus be an economic 1:1 replacement. CITROFOL® AI outperformed the reference emollient in a range of attributes, offering a better gliding effect, lighter consistency, better spreadability and a smoother after feel.
To investigate the potential influence of the solvent matrix on UV absorbance and SPF/UVA-PF, in vitro tests were performed. Neither CITROFOL® AI nor BI interfered with the SPF. Moreover, CITROFOL® AI boosted the UVA-PF by almost 40% compared to the calculated value.
Focusing on certified-natural sunscreen, CITROFOL® AI proved suitable to achieve stable dispersions of inorganic UV filters. The beneficial sensory of CITROFOL® AI was confirmed in a test formulation with inorganic UV filters only. Specifically, consistency was lighter, gliding effect and distributability were more pronounced and the skin feel was much more pleasant than in commercially available benchmarks.
Overall, CITROFOL® AI and CITROFOL® BI showcase remarkable advantages for sunscreen formulations. The excellent solvent power of CITROFOL® BI enables cost-efficient, high-SPF formulation with flexibility regarding co-emollients. CITROFOL® AI is a COSMOS-approved alternative distinguished by a pleasant sensory profile in both formulations based on organic UV filters and those with inorganic UV filters. In addition, it can potentially boost UVA-PF and thus crucially contribute to product labelling with a UVA claim. Both CITROFOL® grades represent outstanding values in the formulator’s palette of emollients for use in sunscreens, optimising performance, costs and consumer experience.