Recent epidemiological studies have demonstrated that air pollution is one of the risk factors for developing skin aging, which is characterized by pigmented spots such as solar lentigos, wrinkles and sagging. Therefore, daily skin care is an important treatment to alleviate the adverse effects of air pollutants on the skin. In this study, we investigated the effects of Phellodendron amurense Bark Extract (PABE) on oxidative stress and the secretion of an inflammatory cytokine by HaCaT keratinocytes treated with diesel exhaust particles (DEP), SRM1975, a model of air pollutants. In general, air pollutants induce a detoxifying enzyme, CYP1A1, and increase oxidative stress through the activation of aryl hydrocarbon receptor (AhR). Treatment with PABE significantly suppressed levels of reactive oxygen species (ROS) and the secretion of IL-8 by HaCaT keratinocytes treated with DEP without affecting the mRNA expression level of CYP1A1. Furthermore, treatment with PABE significantly suppressed the matrix metalloproteinase-1 (MMP-1) activity of normal human dermal fibroblasts (NHDFs) cultured with the conditioned medium of DEP-treated HaCaT keratinocytes. Treatment with PABE increased the mRNA expression levels of γ-GCS and NQO1 due to increased levels of Nrf2. Based on these results, we conclude that PABE alleviates the progression of skin aging due to the removal of oxidative stress without affecting the metabolism of polycyclic aromatic hydrocarbons (PAHs). In conclusion, PABE is expected to be an effective cosmetic ingredient that prevents the acceleration of skin aging by air pollutants.

Although oxidation dyes are the most widely used commercial hair dyes, mechanisms for oxidation product formation and color development of oxidation hair dyes have not been completely elucidated. Moreover, because strong oxidizing agents have been employed in the coloring processes from a practical point of view, the coloring processes would likely result in complications including dye decomposition and polymerization reactions.

Herein, we investigated the oxidation products and the mechanism of color development of oxidation hair dyes under alkaline conditions by air, which is a mild oxidizing agent. The reactions of p-aminophenols as precursors with an equimolar amount of m-aminophenols or resorcinols afforded indophenols, which form 1 : 1 coupling products of both the precursor and coupler. The reaction products and acetylated products were isolated and analyzed by ¹H/¹³C-NMR and high-resolution mass spectroscopy.

The indophenol formation process was explored using a visible spectrophotometer. The changes in the reaction rates and the visible spectra were discussed mainly on the basis of substituent effects. Furthermore, the fading of indophenols during the oxidation process could be suppressed by replacing ammonia with sodium carbonate as the alkaline agent.

Various serine proteases are expressed in the epidermis and influence the barrier function of the stratum corneum. Among these proteases, stratum corneum plasmin is known to have high activity in patients with atopic dermatitis (AD). It is reported that the use of skincare formulations containing tranexamic acid, which has an antiplasmin effect, in AD patients relieved dryness and erythema symptoms and restored the barrier function of the stratum corneum.

To verify the significance of controlling the stratum corneum plasmin activity in AD patients, we examined the changes in stratum corneum plasmin activity before and after the amelioration of skin symptoms in AD patients after using skincare formulations with tranexamic acid. The results revealed that there was a decrease in plasmin activity in the stratum corneum because of the antiplasmin effect of tranexamic acid.

The results indicate that maintaining the stratum corneum plasmin activity at a low level using an antiplasmin agent helps to ameliorate AD symptoms, and skincare formulations containing tranexamic acid may constitute a useful option as a daily skincare product.