In vitro release testing (IVRT) serves as a crucial tool to assess the quality, physicochemical behavior, and performance of semisolid formulations already available on the market. In vitro skin permeation studies (IVPT) are widely used to evaluate the safety and efficacy profiles of topical drugs, utilizing biological membranes prepared from ex vivo human and porcine skin tissues. This study aimed to develop and validate a discriminative IVRT method to evaluate various marketed topical benzoyl peroxide formulations. Additionally, IVPT was employed to assess skin permeation and retention profiles of these formulations, comparing porcine skin results with those obtained by using ex vivo human skin tissues. Physicochemical differences among the evaluated benzoyl peroxide formulations were identified, with the poloxamer-based formulation exhibiting a higher release rate. IVPT using both porcine and human skin differentiated retention and skin permeation profiles, with the poloxamer-based formulation demonstrating greater skin retention capacity compared to the other formulations evaluated. Similar conclusions on benzoyl peroxide retention and cutaneous permeation were drawn from both porcine and human skin IVPT tests, confirming the correlation between the two models.

Skin lipids are essential components that play crucial roles in maintaining the skin barrier, preventing transepidermal water loss, and protecting against external agents. The specific composition of lipids may vary according to factors, such as age, diet, and environmental conditions. They are found predominantly in the stratum corneum, the outermost layer of the epidermis, with lipids originating from epidermal lipids and also from the sebaceous glands. The diversity of lipids, including ceramides, cholesterol, free fatty acids, sphingolipids, phospholipids, triglycerides, and waxes, reflects the complexity of their functions. Understanding the properties and biosynthesis of skin lipids is fundamental for advancing dermatology, developing treatments for various skin conditions, and maintaining the integrity of the skin barrier. Skin microbiome could affect skin lipid composition, and this topic has yet to be completely understood. This literature review aims to understand the properties of lipids found in the skin, the function and importance of fatty acids for skin maintenance and integrity, and their correlations that influence homeostasis: pH, the role of lipids in the microbiota, and finally, daily care practices that can influence the health of the skin and also the microbiome.

Mosquito-borne diseases affect millions of people worldwide each year, and the use of a topically applied insect repellent is an economically viable preventative health practice. The general objective of this work was to encapsulate citronella oil (CO) in a nanostructured lipid carrier (NLC) to formulate a topical repellent with a long duration of efficacy on the skin and a good safety profile based on minimizing skin penetration. In the studied CO, the main chemical constituents of geraniol, citronellal, and citronellol were identified and subsequently used as markers for the in vitro skin permeation testing (IVPT). An optimal NLC encapsulating CO formulation was developed and had an average particle size of 350 nm. The NLC was then formulated in combination with CO at ratios of 2:1, 1:1, and 1:2 CO:NLC-CO as oil-in-water (O/W) emulsions and compared to CO in the same O/W emulsion base (all at 10% CO in the final O/W topical formulation). The markers geraniol, citronellol, and citronellal were detected in all samples tested F1 (10% CO in O/W emulsion) and F3 (10% CO/NLC-CO 1:1 in O/W emulsion). Even the percentages of F3 markers were higher than F1. The recovery of the percentage balance (based on the total remaining on the skin surface, on the skin, and penetrated through the skin to the receptor) of geraniol, citronellol, and citronellal markers for F1 and F3 was 7.70% and 11.96%; 25.51% and 31.89%; and 5.09% and 4.40%, respectively. The nanoparticle lipid solid forms a repellent reservoir on the skin surface, releasing the active ingredients slowly through volatilization, extending the repellent action, and reducing permeation through the skin. It is possible to assume that the remaining 92.30% and 88.03%; 74.49% and 68.11%; and 94.10% and 95.60% of geraniol, citronellol, and citronellal markers of F1 and F3, respectively, were lost to evaporation. In the in vivo efficacy test carried out with the Aedes aegypti mosquito, F3 was the optimal formulation, providing the greatest repellent action compared to free oil in O/W emulsion. Thermal analysis showed that the NLC-CO raised the boiling point of the encapsulated CO compared to the free oil, suggesting that the controlled release of the CO was a possible mechanism for its prolonged effect. We concluded that the nanocarriers developed with CO were stable and provided improved mosquito-repellent efficacy with minimal skin penetration of the CO actives over 24 h. Indeed, regardless of whether the CO was applied as free oil, a 1:1 mixture of CO (pure/free oil) or NLC-CO applied in an O/W emulsion can be considered safe for topical application due to minimal skin penetration.

Cyclodextrins are oligosaccharides, specifically cyclic α-1,4-D-glucose oligomers, that possess a cone-like shape resulting in a hydrophobic inner cavity capable of forming complexes with several guest molecules in a hydrophilic matrix. This capability has led to an extensive investigation into cyclodextrin applications in several different substrates with the purpose of overcoming limitations, such as solubility issues, physical degradation and sensitivity to solvents, in guest substances. Researchers have recently described successful interactions between cyclodextrins and proteins, such as enzymes, peptides and amino acids. These complex biomolecules consist of potent active ingredients and are employed in several industrial biocatalyst processes. However, this group in particular tends to have limited usage in pharmaceuticals due to its natural processes of degradation and instability in unusual environments, frequently requiring accurate procedures and stabilization methods in all stages of production. In several cases, the final product still has a short shelflife and often requires a controlled environment for storage. The formation of a cyclodextrin supramolecular complex could not only prevent such problems, but also enhance the intrinsic characteristics of guest substances, thus allowing for an expansion in their industrial production and application. This work focuses on cyclodextrin interactions with proteinlike structures in order to describe their possible applications in the formulation of pharmaceutical proteins.