The goal of this research was to study the factors influencing the in vitro transdermal penetration of nicotinamide and to establish an evaluation method for the in vitro transdermal absorption of nicotinamide. The permeability of nicotinamide was investigated with Franz diffusion cell in vitro transcutaneous assays, and the effect of the receiving solution composition, receiving solution pH, skin type, diffusion cell temperature, active ingredient concentration, supply quantity, and product dosage form on its permeation was investigated separately by high-performance liquid chromatography. The best assay for the transdermal absorption of nicotinamide was established—there was a better transdermal absorption performance, more stable system, better applicability, and better reproducibility when the receiving solution was PBS (phosphate-buffered saline) solution, the pH was 7.4, the membrane was pig ear skin, the temperature was 37 °C, the concentration of nicotinamide was 3%, and the dose of the test substance was 2 g. In the three cosmetic dosage forms of toning lotion, milk lotion, and gel, the permeability of milk lotion was the highest, followed by toning lotion and gel.

The ideal UV absorber should be safe and should have excellent properties. Therefore, transdermal absorption is essential for the safety risk assessment of sunscreen cosmetics. The Franz diffusion cell method is the most common means of studying in vitro penetration, but there is a lack of standard methods for the in vitro permeation of UV absorbers. This paper used the Franz diffusion cell method to improve an in vitro permeation test (IVPT) for UV absorbers; three commonly used UV absorbers were tested: Octinoxate (EHM), Diethylaminohydroxybenzoyl hexyl benzoate (DHHB), and Ensulizole (PBSA). The final parameters were as follows: porcine ear skin was chosen for the membrane; the temperature of the receptor fluid was 37 °C; a PBS solution with 50% ethanol was chosen for the receptor fluid; and the dose of the test substance was 3 g. The improved IVPT method will help to accurately quantify the in vitro permeation of difficult-to-permeate components. In addition, the method can also be applied to evaluate the permeability of UV absorbers under different formulation conditions, which will help to address the difficulties related to the safety and application of sunscreen products.

Thanaka powder is a natural and safe biomass material that can be used in the preparation of Pickering emulsions. It contains lots of hydrophilic phenolic hydroxyl groups, making it highly hydrophilic and leading to emulsion instability, which further limits its application in the cosmetics industry. In this paper, Thanaka powder was modified to improve its stability. The modified Thanaka powder was characterized and was used to prepare Pickering emulsions. The results showed that the stability of the Pickering emulsion increased with the increase of the solid particle concentration; the suitable oil-water ratio helped to obtain the Pickering emulsion with good stability; the different aqueous phase environments had little effect on the particle size variation of the emulsified particles; the emulsions exhibited shear thinning behavior. This study offers valuable insights into the research, development, and commercialization of Thanaka-based skincare products, thereby expanding the applications of Thanaka powder.