Criticisms in the Development of High-Protection and Broad-Spectrum “Natural/Organic” Certifiable Sunscreen

Abstract

Attention to environmental issues has become increasingly important in recent years and also massively affects the cosmetics sector. In this context, sunscreens are questioned due to the proven or believed ecotoxicity of organic ultraviolet (UV) filters. This has pushed developers increasingly towards the use of inorganic filters, which can prove difficult to spread with low compliance. We faced the problem by proposing a rational approach based on the evaluation of the morphology of the inorganic material, as the real dimension does not often correspond to the characteristics declared by the producers because the material itself tends to aggregate. A combination of a specially selected inorganic filter is required to formulate Cosmetic Products with a Natural and Sustainable Connotation (CPCNS) standards.

Standardizing the White Cast Potential of Sunscreens with Metal Oxide Ultraviolet Filters

“…This assignment was reinforced by scanning electron microscopy (SEM) imaging that displayed aggregated crystalline solids of ZnO in Sunscreen C, whereas Sunscreen B displayed fewer aggregates, with a more porous ZnO surface. 36 These visual results are consistent with increasing formulation viscosity leading to lower ease of spreading and therefore increased white cast. The viscosity increased in all formulations over time, resulting in more agglomeration and less aesthetically pleasing applications of the formulations with sunscreen age (i.e., after one month).…”

“…In the macroscopic assay, Sunscreen Formula C displayed visibly increased aggregation of ZnO particles and less film uniformity (see white spots in the image in Figure 6), which is due to the increased viscosity and density of the dispersion with stearic acid. 36 Sunscreens A and B demonstrated the best film uniformity, and Sunscreen B displayed a slightly lower density of white spots against the black paper than Sunscreen Formula A did, which we attribute to the incorporation of a ZnO dispersion rather than free ZnO powder (Figure 6). While Sunscreen C technically demonstrated the most transparency against the black paper, we attribute this result to the lower ease of spreading associated with stearic acid's dispersion of ZnO aggregate and agglomerations, resulting in visibly inconsistent agglomeration and therefore transparency of the film (see white spots on Figure 6).…”

“…Sunscreens A, B, and C spread against black paper for macroscopic observation using optical microscopy. Reproduced with permission from ref . Copyright 2022 The Authors.…”

“…While Sunscreen C technically demonstrated the most transparency against the black paper, we attribute this result to the lower ease of spreading associated with stearic acid’s dispersion of ZnO aggregate and agglomerations, resulting in visibly inconsistent agglomeration and therefore transparency of the film (see white spots on Figure ). This assignment was reinforced by scanning electron microscopy (SEM) imaging that displayed aggregated crystalline solids of ZnO in Sunscreen C, whereas Sunscreen B displayed fewer aggregates, with a more porous ZnO surface …”

“…To highlight this challenge between viscosity and white cast, Tortini et al compared the chemical and physical properties of sunscreen formulations with varying rheological modifications. 36 They formulated three water-in-oil sunscreens (Sunscreens A, B, and C in Figure 6), where Sunscreen A contained 25% w/w% composition of free ZnO powder, Sunscreen B contained 25% w/w% composition of a ZnO dispersion (International Nomenclature Cosmetic Ingredient, INCI, list: ZnO, sodium lauroyl glutamate, lysine, MgCl 2 ), and Sunscreen C contained 25% w/w% composition of another ZnO dispersion (INCI list: ZnO, stearic acid). The remaining ingredients in each formulation were identical, and physicochemical properties (i.e., pH, viscosity, visual appearance) of the sunscreens were measured at day zero at 25 °C, one month afterward at room temperature, and one month afterward at 45 °C.…”