Due to the growing awareness of UV protection in recent years, many people have come to use sunscreens in various scenes. However, in leisure and sports scenes, sweat and water may wash them off and the expected UV protection effect may not be obtained. Therefore, in the development of sunscreen formulations, it is important not only to enhance the UV blocking effect, but also to have water resistance technology to maintain the effect. In this review, we will introduce the basic knowledge of UV protection materials and formulation development technology used in sunscreens, and the development of materials that achieve both high SPF/PA and water resistance.
Ceramide is one of the main components of stratum corneum intercellular lipids and it plays an important role in barrier function. Although ceramide is a useful material for cosmetic products, it is difficult to stably mix into formulations, especially oil-poor formulations such as lotions, because of its highly crystalline nature. In stratum corneum intercellular lipids, ceramide forms flat lamellar structures with cholesterol, free fatty acids, and other lipids. Thus, we assumed that a flat shape would be suitable for the formulation of a stable ceramide mixture, and we focused on bicelle discoidal aggregates, which have a flat part composed of long-chain phospholipids and a rim composed of short-chain phospholipids or nonionic surfactants. We succeeded in preparing a translucent and stable lotion by mixing ceramide 2, hydrogenated soybean lecithin, and polyoxyethylene phytosterol ether in an appropriate ratio, and we confirmed that the lotion contained bicelles by transmission electron microscopy and X-ray diffraction. Differential scanning calorimetry showed that the crystalline structure of ceramide was weakened in the bicelles. X-ray diffraction indicated that the bicelle lotion formed a lamellar structure when it dried. These results suggest that bicelles can enable high concentrations of ceramide to be mixed stably into lotion, and that the bicelle lotion is occlusive. Since bicelles can be prepared without high-energy procedures such as high-pressure treatment, bicelle lotion is expected to be beneficial not only as a skincare item, but also as a sustainable formulation.
Emotions affect some biological functions on the skin. In fact, it has been reported in various studies that negative emotions cause worse skin conditions. The relationship between positive emotions and skin conditions, however, has remained unclear. Previously, the efficacy of skincare has been discussed mostly from the dermatological point of view, such as active ingredients and formulation technologies. On the other hand, various emotional changes occur during the process of using cosmetics, and they could also relate to skin conditions. Based on the assumption that positive emotions improve skin conditions, we examined whether the pleasant touch of softly touching the whole face with the palms of both hands, i.e. a hand-press, leads to good skin appearance by using the sensual visual assessment. First, we found that the skin appearance score for “Smoothness” changed positively with performance of the hand-press and it led to favorable skin scores in other aspects of appearance, such as “No dryness” and “Clarity”. Next, we investigated skin appearance influenced by positive emotions resulting from the hand-press method. In the second trial, all participants performed the hand-press. Based on the positive emotions score, participants were divided into high-score and low-score groups; then the extent of change in skin appearance was compared between them. In the high-score group, the scores for “Radiance”, “Moisture”, “No dryness”, “No dullness” and “Less yellowness” were significantly higher than in the other, with a marginally significant difference for “Clarity”. These results showed that a positive state of mind generates better skin condition, indicating that a psychological approach is useful for improving skin condition in a different manner than a purely dermatological approach.
Hair color is one of the factors that affect the impression of a person. Various characteristics such as gloss and ‘clearness’ are often perceived with hair color. However, it has not been clarified yet how hair color and gloss can be perceived as harmonious, and how hair can be perceived as ‘clear’. In this study, we conducted experiments using 16 combinations of hair color and gloss and 22 evaluation words to quantitatively measure the effect of hair color and gloss on perceived impression and ‘clearness’ of hair. We analyzed the data using a two-factor ANOVA, path analysis and multiple regression analysis. The results showed that for some evaluation words the value increased monotonically with increasing gloss regardless of hair color, whereas for other evaluation words the value was highest for medium gloss. In addition, the path diagrams suggested that the factors which determined whether the gloss suits the hair color are different for each hair color. Furthermore, the multiple regression model explained more than half of the perception of ‘clear’ hair. Clarifying the relationship between hair color and gloss will enable us to extend the range of color design expression more effectively and apply it to new product development with novel concepts.
In this study, we propose “Tangible Skincare” which aims to improve the quality of life (QOL) of the skincare users. In order to improve their QOL through skin care, it is essential to design the cosmetic products considering scenes in the users' lifestyles in addition to the conventional improvement of the skin condition. Therefore, we focused on the busy working women whose number is recently increasing and observed their skin conditions. According to our consumer survey of working women, almost all working women have skin roughness like scales. Furthermore, it was found that these scales resulted in a terrible make-up finish and also affected the QOL of working women. In order to tackle this problem, a novel skincare approach for prompt skin surface improvement is crucial. The key for this approach is to incorporate an “adhesive polymer”, which adsorbs peeled corneocytes selectively and re-adheres, into a conventional skincare formulation exhibiting high moisture effect. We developed a novel formulation by using this approach. According to the usage test of our novel formulation, this formulation was found to improve skin roughness within only 3 d. Furthermore, this prompt skin surface improvement gives a better make-up finish from both appearance and tactile viewpoints in working women's daily lives. As a result, it was confirmed that such skin improvements with 3 days' care is tangibly recognized by women from the two perspectives (visible and tactile) and enhances their QOL.
A novel “pearl” luster develops in low-concentration aqueous solutions composed of cetanol as a higher alcohol and polyoxyethylene (20) polyoxypropylene (4) cetyl ether as a surfactant. To elucidate the mechanism by which this pearl luster manifests, we simultaneously measured the small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) on the aqueous solutions at a synchrotron radiation facility (SPring-8). The SAXS profile of a 15 wt% mixed-sample solution at 40°C showed multiple sharp peaks. The higher order peaks were observed at the scattering vector (q) positions, which were integer multiples of the primary peak position, suggesting a lamellar structure formed. On the other hand, the WAXS profile showed a sharp diffraction peak near q=15 nm-1 at 40°C, which indicates the formation of an association structure derived from α-gels. The scattering profile exhibited no peaks attributable to a long-period structure for a 2.5 wt% mixed-sample solution. However, as there was a diffraction peak of the α-gel-derived structure in the WAXS profile, we believe that this structure is involved in the pearl luster formation. The aforementioned results suggested that the pearl luster solution is a dispersion possessing a bilayer structure, and we surmised that the pearl luster is the result of multiple light reflections by the dispersion. Our findings were applied to cosmetic lotions, and the pearl luster lotion with an α-gel structure was beautiful in appearance. It was suggested that the confined water present in the α-gel structure contributes to the moisturizing effect of the lotion.
The risk of eye irritation due to drugs is determined primarily by the in vivo rabbit eye irritation test (Draize test) described in the OECD TG 405 and generally labeled by the Globally Harmonized System of Classification and Labeling of Chemicals (GHS). In the interest of animal protection, the development of in vitro alternatives to animal testing not involving the Draize test are being pursued. In this study, we examined whether the GHS eye-irritation classification could be predicted using the Hansen solubility parameter (HSP). Hansen spheres were created based on the safety information of the test substance and its HSP values, and the potential parameters were obtained. By comparing these potential parameters with the HSP value of each test substance, the GHS classification was predicted. For substances that cause serious damage (GHS category 1), the prediction accuracy was 87.7% (64/73), false-negative rate 26.7% (4/15), and false-positive rate 8.6% (5/58). For substances not classified as eye irritants (GHS not classified), the accuracy was 87.7% (64/73), false-negative rate 9.5% (4/42), and false-positive rate 16.1% (5/31). These data suggest the possibility that eye-irritation classified by GHS can be predicated with high accuracy by comparing the potential parameters to the HSP of test compounds.