Over the last few years, there have been incidents where cosmetics were recalled due to microbial contamination. An important feature of cosmetics is that when consumers use them they feel safe and confident in doing so from start to finish. This paper has summarized precautions when designing products with a high risk of secondary contamination to preserve them. In addition, frequently used preservatives, the status of international regulations on preservatives, and factors that affect preservative efficacy (antimicrobial effectiveness) are mentioned. In response to increased safety consciousness among consumers and foreign regulations of preservatives, products need to be formulated and designed without parabens or other preservatives. We have examined the antimicrobial effectiveness and sensory irritation of the skin by 1,2-alkanediols in comparison to parabens. Results revealed that 1,2-alkanediols and parabens have almost the same level of antimicrobial effectiveness and that 1,2-alkanediols cause significantly less sensory irritation than parabens do. The hope is that these findings can help researchers to devise ways to preserve cosmetics while ensuring appropriate product quality during cosmetics development.
Dullness of the skin around the eyes is one of the most serious cosmetic problems. However, the causative mechanism of skin dullness, especially in the skin of the upper eyelids, remains unclear, and effective treatment needs to be established. The skin of the upper eyelids is particularly exposed to mechanical stimulation such as compression or friction by repetitive and multiple applications or removals of make-up. Mechanical stimulation has already been reported to induce hyperpigmentation of the skin. We hypothesized that dullness of the skin of the upper eyelids might be caused by melanin formation through mechanical stimulation. We conducted two experiments using reconstructed human skin models; the first experiment showed that repetitive loadings of weight resulted in the activation of melanogenesis, and the second one demonstrated that the activation of melanogenesis was inhibited by the addition of a nitric oxide scavenger. These results suggest that nitric oxide is involved in mechanical stimulation-induced melanogenesis. In addition, a skin lotion containing nitric oxide scavenging preparation, wasuregusa flower ferment filtrate, did not reduce the dullness of the skin of the cheeks, where the relative frequency of mechanical stimulation is low, but did reduce that of the upper eyelids. These results support our hypothesis that mechanical stimulation contributes to the dullness of the skin of the upper eyelids and suggest that nitric oxide plays an important role in mechanical stimulation-induced melanogenesis. Therefore, nitric oxide and its generation need to be targeted to reduce skin dullness.
We investigated the development of an o/w emulsion with a good texture of use and waterproofness. We considered the Gemini-type surfactant, which can disperse oil using a small amount of emulsifier, to be suitable to achieve the objectives, and investigated using sodium dilauramidoglutamide lysine (International Nomenclature of Cosmetic Ingredients (INCI) name; a Geminitype compound obtained by treating sodium lauroyl glutamate with lysine). We report that the expected good results were obtained. The critical micelle concentration of sodium dilauramidoglutamide lysine was found to significantly decrease compared with a monomer (sodium lauroyl glutamate), and we evaluated the emulsifying capacity. As a result, sodium dilauramidoglutamide lysine, can emulsify various types of oil with a small amount (0.03 to 0.1%) regardless of the blended amount (10 to 50%), and the emulsion showed good stability (almost no change in the particle size between the baseline and after 1 month at 50℃). In a comparison of the waterproofness between the emulsion prepared with sodium dilauramidoglutamide lysine and that emulsified by a non-ionic surfactant using the cup-shaking method, the former contained more components in the oil phase in the skin or hair. In addition, it was less oily, could be spread more smoothly, and provided a fresh texture of use after application compared with a non-ionic surfactant since it was emulsified in a small amount.
Keratotic plugs emphasize pore perceptibility. We examined the structural features of keratotic plugs histologically and found that keratotic plugs were compartmentalized with rigid cell layers and derived from the inner root sheath of hair follicles. These results argue against the hypothesis that keratotic plugs consisted of aggregates of sebum and corneocytes. The keratotic plug formation was also associated with activation of androgen. Fermented pomegranate as an active ingredient not only decreased the expression of the GATA3 gene involved in the formation of inner root sheath which is a component of keratotic plugs, but also enhanced the expression of the 17β-hydroxysteroid dehydrogenase type 2 gene associated with inactivation of androgen. On the assumption that the active ingredient acts as an improving agent for keratotic plugs and pore perceptibility, a milk lotion containing the fermented pomegranate as an active ingredient was prepared and a user trial was performed with female subjects. The results show the reduction of keratotic plug formation and the improvement of pore perceptibility, indicating that the active ingredient is useful for cosmetic purposes.
Antimicrobial agents are used in deodorants to inhibit the growth of bacteria that transform sweat and sebum secretions into odorous compounds. In this study, we examined the ability of antimicrobial agents to enhance the deodorant effects. We first assessed changes over time in residual amounts of 4-isopropyl-3-methylphenol (IPMP) and 2,4,4′-trichloro-2′-hydroxydiphenyl ether (Triclosan) on axillary areas following the use of deodorants. The results suggested that the residual performance of Triclosan was significantly higher than that of IPMP. Second, in order to elucidate the causes of these reductions of the agents on axillary areas, we chose several factors and evaluated each contribution ratio. The results suggested that the primary factors were internal skin penetration and transition to clothes through sweat. Finally, we developed a screening method to evaluate the effects of the deodorant keeper that enhanced the residual performance of antimicrobial agents on the skin. The screening revealed that the deodorant keeper required certain characteristics: high molecular weight, high hydrophobicity and high affinity with antimicrobial agents. In the case of the deodorant keeper for IPMP, the polarized sites on the structure of the ingredients led to high affinity for IPMP because the dipolar interaction was enabled.
In the solubilization of β-Glycyrrhetic Acid (GA) in an aqueous solution of Lauryldimethylamine Oxide (AO), it was found that the viscosity of the solubilized solutions consisting of GA and AO (GA/AO) increased with the increase of the concentration of GA. Furthermore, the viscosity of GA/AO decreased with the increase of pH value caused by the addition of KOH. In this study, the micellar structure of GA/AO was investigated by using small-angle X-ray scatte ring (SAXS). From this analysis, it was recognized that the micellar shape and size changed with GA concentration and pH value.