Cosmetics including quasi-drugs are used daily and for a long period of time for the purpose of improving the quality of life (QOL) of people; therefore it is essential to ensure the safety of cosmetics. Cosmetics are composed of a wide variety of raw materials and ingredients, and not only their dosage forms, but also their application parts and usage methods are diverse. Therefore, it is necessary to assess and guarantee safety according to various situations from raw materials to products and use scenes. In addition, in order to assess safety appropriately, it is necessary to understand a lot of information such as the background of the times, laws, regulations, various evaluation methods and guidelines. This review introduces a wide range of contents that should be understood in order to assess and guarantee safety, including the history of the safety of cosmetics, based on the basic information on actual safety assessment.

Skin Translucency is one of the most important factors for beautiful skin. As the investigation of the relationship between skin physiological characteristics and skin translucency has progressed in recent years, methods for the objective evaluation of skin translucency have been proposed. However, the proposed evaluation methods do not sufficiently reveal the interaction between translucency and skin physiological characteristics. In addition, they are unable to quantitatively indicate which skin physiological characteristics affect skin translucency. To solve this problem, we aimed to develop a mathematical model of skin translucency that describes the interplay among skin physiological characteristics and obtain a mechanistic understanding of the improvement of skin translucency. We attempted to analyze the relationship between a visual observation translucency score and skin physiological characteristics by combining several statistical methods. As a result, a linear model that shows the relationship between translucency and skin physiological characteristics was developed using multiple regression analysis. Our model analysis identified “red spot count” and “skin smoothness” as key characteristics that dictate skin translucency. Furthermore, by adding discriminant analysis, we estimated that skin elasticity, wrinkles, and porphyrins affect skin translucency. Our model also suggested that the interplay between skin translucency and skin characteristics detected by discriminant analysis may differ among individuals. Our model provided quantitative and coherent explanations for mechanisms behind skin translucency. This system-level mathematical approach can be used to uncover individual factors reducing skin translucency and investigate new and better treatment options to improve skin translucency.

The area around the eyes creates a very strong visual impression. As eye shadow is an effective tool for improving that impression, it is used across a wide range of age groups. On the other hand, the area around the eyes is very susceptible to aging, dullness, sagging, and wrinkles, and is a concern for many. To mask the effects of aging and improve the impression made, eye shadow needs to correct and flatten wrinkles, eliminate dullness, brighten and add gloss to the area around the eyes, and create a feeling of firmness. However, irregularities on eyelids, such as wrinkles and the grooves of double eyelids, are more prominent than in other areas, making it difficult to create a flat, uniform, bright, and glossy surface. Furthermore, since eyelids frequently move forcefully during blinking, maintaining the durability of cosmetics has been a challenge. In this study, we focused on polyurethane in order to achieve a glossy and elastic eye shadow that is unaffected by movement. Our newly developed polyurethane contains highly-flexible oil-soluble soft segments and hard segments that form hydrogen bonds. Using this material, we created a gel from the oil with a reverse micelle structure. Our polyurethane-based oily-gel eye shadow not only provides gloss to aged eyelids but also offers resistance during blinking and other eye movements.

Lip-dullness is one factor of significant concern impacting facial beauty. However, an objective approach for evaluating lip-dullness has yet to be proposed. Therefore, to establish an objective evaluation method for lip-dullness, we examined the feasibility of using the spectral reflection characteristics of lips by analyzing the reflection spectra of the lips of 30 subjects and searched for a spectral reflection pattern corresponding to lip-dullness. First, the 30 subjects were classified into three groups based on visual evaluations of lip-dullness. Then the spectral reflectance spectra of all subjects' lips were acquired and analyzed. Specifically, we focused the ratio of maximum reflection intensity in the green region (I_G) to the maximum reflection intensity in the red region (I_R), that is, I_G/I_R. When the I_G/I_R values were plotted for the three groups, a strong positive correlation was observed between the I_G/I_R values and the visual evaluation results. In order to verify the validity of I_G/I_R value as an evaluation index, the I_G/I_R value was changed using lip gloss containing Red No. 7 or 30, and the changes in visual evaluation were observed. As a result, it was confirmed that I_G/I_R values and visual evaluation results remained highly correlated, demonstrating the usefulness of the I_G/I_R value as an objective evaluation method.

It is necessary to establish an in vitro sun protection factor (SPF) test that considers costs, time requirements, and ethical problems. However, few studies on in vitro SPF tests for powder products, which do not easily create uniform layers on polymethyl methacrylate (PMMA) plates, have been reported so far. To produce uniform layers, solvents were applied on PMMA plates before applying powder products. This study aims to clarify the impact of various factors on in vitro SPF values of the powder products and establish an in vitro SPF test method that correlates with in vivo SPF values. Temperature variations affect the solvent viscosity, leading to significant differences in the in vitro SPF values. Therefore, we selected mineral oil because its viscosity is not strongly affected by the temperature. Based on the combinations of the amounts of solvents and samples, the confidence interval (CI[%]) varied. Therefore, we selected 0.3 mg/cm² of sample against 0.1 mg/cm² of solvent for the combination with CI [%]≤17. We identified significant differences in the in vitro SPF values depending on the number of spreads. Therefore, we defined the number of spreads as 10 reciprocations × 4, which had the smallest 95% confidence intervals (95% CI). We could not identify significant differences upon varying the spreading pressure. However, when the spreading pressure was (1.18±0.20)N, the CI [%] was higher than 17. Therefore, we chose (0.69±0.20)N, which had the smallest 95% CI. A single-regression analysis between the in vitro SPF values obtained by applying the conditions established in this study and the in vivo SPF values according to ISO 24444:2010 showed that the coefficient of determination was 0.9486 (r=0.9739). Thus, we successfully established an in vitro SPF testing approach for powder products.

Regarding effects of cosmetics on our minds, there is limited information on whether different cosmetic categories can be associated with human emotions. Therefore, we conducted an internet survey to assess emotions and attitudes of 2340 Japanese women, aged 20-44 yrs, and cataloged their opinions on 10 categories of skincare and make-up cosmetics. Emotions are defined as a level of arousal, while attitudes are defined as an actualized recognition of self-consciousness. Survey results revealed “relaxed and refreshed” and “energetic and cheerful” as emotion factors, and “introvert” and “extrovert” as attitude factors. Results of the survey indicated that participants were “relaxed and refreshed” when using skincare products and they were “energetic and cheerful” and “extrovert” when using make-up products, in line with previous studies. Moreover, the survey revealed that each cosmetic category is associated with specific emotions and attitudes. Although skincare products were associated with “relaxed and refreshed” feelings, women reported less of such feelings when using moisturizers and face creams than when using other skincare products; similarly, women felt less “energetic and cheerful” when using primers and foundations compared to other make-up products. On the other hand, serums had a high association with “energetic and cheerful” and “extrovert” while make-up removers and face creams had a low association with “introvert.” The survey also revealed that emotions and attitudes towards skincare products are different during morning and night. “Energetic and cheerful” was experienced more in the morning and “relaxed and refreshed” and “introvert” were experienced more at night.

Damaged hair has 14% lower strength and elasticity and a smaller hydrophobic hair surface area than those of undamaged hair. A previous study found that diglucosyl gallic acid (DGA) and trimethyl stearylammonium chloride (STAC) increase the surface hydrophobicity of damaged hair. Moreover, we have confirmed that DGA can improve hair strength and elasticity. Although STAC alone does not restore the strength and elasticity of damaged hair, a DGA+STAC combination can repair damaged hair at the surface and cuticle layers and achieve strength and elasticity equivalent to those of non-damaged hair. We investigated the performance of DGA+STAC as a restoring agent through time-of-flight secondary ion mass spectrometry (ToF-SIMS) and scanning electron microscopy. The STAC peak intensity (measured by ToF-SIMS) of damaged hair was higher for hair treated with DGA+STAC than that for hair treated with STAC alone. The results suggested that DGA+STAC interacts with both the top-surface and cuticle layers of damaged hair to effectively restore its hydrophobicity, strength, and elasticity.