Efficiency of emulsifier‐free emulsions in delivering caffeine and α‐tocopherol to human skin

Abstract

Objective Increasing consumer demand for natural and environmentally friendly products is driving the cosmetic industry to seek greener and safer processes. High‐frequency ultrasound technology (HFUT) stabilizes emulsions without adding emulsifying surfactants (ES). In this work, the formulation characteristics of an HFUT‐treated emulsion and a Reference emulsion were compared for both caffeine and α‐tocopherol. Methods A comparison was made between ES‐free emulsions and the Reference emulsions based on droplet size, viscosity, pH and rheology behaviour for both active cosmetic ingredients. The permeation of caffeine and the skin retention of α ‐tocopherol were studied in vitro using Franz diffusion cells on human skin biopsies, considered the gold standard for permeation assays. Results The formulations developed were stable and showed suitable droplet size distribution. In the case of ES‐free emulsions, the average droplet size was inferior to 1.5 μm regardless of the polarity of the active. All formulations presented a shear‐thinning pseudoplastic behaviour, an attribute usually desired for cosmetic products. The skin permeation studies showed that in the case of caffeine (model hydrophilic molecule), the ES‐free emulsion presented a delivery capacity similar to that of the Reference emulsion. However, for α‐tocopherol (highly lipophilic model molecule), differences were observed in the distribution of the active in the stratum corneum with an advantage for the Reference emulsion, probably due to the impact of surfactants on the SC lipids. Conclusion This work demonstrates that HFUT is a reliable tool that is able to prepare stable ES‐free emulsions loaded with hydrophilic or lipophilic active ingredients. Skin permeation studies confirm that the emulsions produced by HFUT promote the delivery of the actives to the human skin. In the case of α‐tocopherol, the delivery efficiency was lower than with the Reference emulsion, especially in the SC layers, due to the absence of surfactants. Nevertheless, the ES‐free emulsion still represents a good compromise between efficacy and the need for green cosmetics in the market.

Ultrasmall Solid-Lipid Nanoparticles via the Polysorbate Sorbitan Phase-Inversion Temperature Technique: A Promising Vehicle for Antioxidant Delivery into the Skin

“…In fact, the presence of hair follicles on the skin models adopted for this experiment is not homogeneous, and this may account for the variation in the obtained experimental evidence [ 21 ]. Due to its low solubility, TOCO has been extensively loaded in lipid-based cosmetic and/or dermatological formulations [ 22 , 23 , 24 , 25 , 26 , 27 , 28 , 29 ]. According to recent literature, ultrasmall PIT SLNs allow a relevant skin permeation, vs. both skin accumulation from the same SLNs and permeation from control suspension.…”

α-Tocopherol: New Perspectives and Challenges for Achieving the Sustainable Development Goals (SDG) Target

“…It should be noted that it is important to consider a good compromise between efficacy and the need for green cosmetics in the market. Therefore, the emulsifier-free nanoparticle seemed still nice representative, though the delivery efficiency of α-Toc was lower than with the reference emulsion 99) . In terms of the problematic issue of synthetic VE, (all-rac) -α-Toc seemed induce dermatitis more frequently than natural origin, and higher concentration of VE in its pure oils can enhance the risk of them causing allergic contact dermatitis 93) .…”

Caffeine-Containing Emulsion: Influence of the HLB and Mixing Proportions, the Oil’s Chemical Composition, and the Existence of Caffeine on Emulsion Properties

“…Their ease of preparation, excellent performance, and outstanding stability make them highly appealing for large-scale production . Although some studies on caffeine emulsion in various systems, including emulsifier-free emulsions, multiple emulsions (W/O/W), O/W emulsions, and W/O emulsions, , have been reported, the impact of oil’s chemical composition on emulsions’ properties has not been explored for all formulations.…”