In the present review, natural and non-toxic particles made of micro/nanocellulose were specifically targeted as stabilizers of emulsions located at dispersed and continuous phases interfaces (called Pickering Emulsions, PEs). PEs are biphasic systems stabilized by solid particles with a recent interest in food and cosmetic domains. PEs have been more and more studied in the last ten years due to their advantages compared to conventional emulsions with surfactants. PEs have already been stabilized with various types of particles and particularly cellulose. Even if some studies showed that PEs were more stable when cellulose was chemically modified, numerous other recent studies showed that unmodified micro/nanocellulose is also promising biomaterial to stabilize PEs. Micro/nanocelluloses can be extracted by various green processes from numerous agricultural wastes and co-products, as banana peels, corncob, ginkgo seed shells, lime residues, mangosteen rind, oil palm empty fruit bunches, pistachio shells, as well as wheat straw. Main green processes used to treat cellulose are grinding, high pressure homogenization, microfluidization, enzymatic hydrolysis, subcritical water, extrusion, electron beam irradiation, cryocrushing, microwaves or sonication. PEs formulated with cellulose clearly participate to a global sustainable development but, additional studies will be necessary to better understand PEs stability and improve properties.

Objective The cosmetic industry endeavours to strengthen the greener and safer claims of processes to respond to the high demand from customers for natural and environmentally friendly products. High‐frequency ultrasonication technology (HFUT) is a physical process enabling the stabilization of emulsions without requiring additional ingredients, such as emulsifying surfactants (ES) to be introduced into the formulations. In this study, key formulation characteristics of an emulsion synthesized by HFUT and a reference emulsion (RE) were compared, as well as the permeation kinetics of caffeine, used as a model active cosmetic ingredient, from both types of emulsions. Methods The pH, droplet size and viscosity of emulsions prepared by the HFUT and the RE were determined and compared. The permeation of caffeine from the HFUT emulsion and the RE applied to the surface of reconstructed human epidermis (RHE) models was compared. Results The ES‐free formulations prepared by HFUT displayed a nearly 2‐fold lower average droplet size and over 3‐fold greater viscosity, compared to the RE. Despite these differences, the absence of ES in the HFUT emulsion did not significantly alter the permeation kinetics of caffeine through RHE. The caffeine steady‐state flux, lag time and permeability coefficients differed by 20%–30% only. Conclusion This study demonstrates the potential of the HFUT to yield topical cosmetic products with lower requirements ingredients‐wise, without losing efficacy, supporting the possible implementation of the technology in the cosmetic industry.

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.