Maintaining suitable skin hydration is very effective for preventing dry skin. This is the most basic and important function of cosmetics. Various types of emollients and humectants are used in skincare products to prevent water loss from the skin and retain water. In the stratum corneum, the importance of natural moisturizing factor (NMF), sebum and intercellular lipids has been demonstrated. From a dermatological approach, we have already reconstructed an analogy of the skin hydration mechanism. For dry skin, we have demonstrated the usefulness of “moisture balance;” that is, to supply equivalent substances of water, humectants and oils in cosmetics. It is also important to develop cosmetics from a pharmacological approach. This is very helpful in the development of new, more effective components for cosmetics. Recently we have clarified the important role of epidermal protease activity in dry skin. Inhibition of its activity accelerates intercellular repair response. We have developed trans-4-aminomethyl cyclohexane carboxylic acid (t-AMCHA), which has an anti-plasmin (a epidermal protease) activity and can cure dry skin. This article reviews the skin hydration mechanism and development of skin care cosmetics utilizing dermatological and pharmacological approaches.

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Thick or stiff feeling hair is thought to be due to a complex combination of several physical properties. Torsional stress and bending stress play an important role in the physical properties of human hair, Rigidity, as modulus of rigidity from a material dynamics viewpoint, was evaluated, Based on the estimated diameter of the minor and major axes of hair, torsional stress was evaluated as a modulus of rigidity. Evaluation of the modulus of rigidity of intact hair and delaminated hair, from which cuticles were removed by physical stripping, enabled estimation of the modulus of rigidity of the cuticle. The results indicated that the modulus of rigidity of the cuticle was approximately 3.5 times than that of the cortex. The contribution of the cuticle on the torsional stress of whole hair was also evaluated. The contribution of the cuticle on the torsional stress of whole hair was found to be as much as 60%. Since the cuticle contributes to a large part of torsional stress as well as bending stress, it is assumed that the cuticle plays an important role in the thick or stiff feeling of hair. The ratio of Young's modulus versus the modulus of rigidity of hair was calculated to be 11.94, which is larger than that of uniform material. Since the cuticle and cortex can play the part of composite material, it is quite reasonable that the larger value of the ratio of Young's modulus versus the modulus of rigidity of hair was found in hair, which is a complicated structure combining both cuticle and cortex.

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Wrinkles and sagging are types of age-induced changes in facial morphology, and these changes become more noticeable with age. Due to individual differences, age-induced changes progress at different rates, and thus the degree of wrinkles and sagging varies among people in the same age group. Various factors contribute to individual differences, and we hypothesized that facial configuration, namely facial contour and the size and location of the eyes, nose and mouth, is one such factor. Therefore, the present study investigated whether or not individual differences in age-induced changes in facial morphology, such as wrinkles and sagging, could be explained in terms of individual differences in facial configuration. The facial configurations of subjects were determined by examining photographs taken of subjects approximately 20 years of age, and then wrinkles and sagging were assessed for the same people after they had aged several decades, The results of a discriminate analysis showed that laugh lines are more noticeable for people with large eyes, thus suggesting that ageinduced changes in facial morphology are related to certain aspects of facial configuration, namely to certain favial dimensions.

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A new dispersing agent was synthesized by introducing a vinyl pyrrolidone group into the acrylate/dirnethicone acrylate copolymer. The graft copolymer formed a layer throughout surface of each particle, As a dispersing agent, it showed unique and excellent properties when it is used to disperse inorganic fine powder in volatile silkone oil, Introducing the adsorption segment improved its dispersion ability to be stable not only in silicone oil but also in mixtures containing ester oil or UV absorbent. Since the application film containing the new graft copolymer was superior in water resistance, it was found that it maintains a UV protection effect and high transparency through waterproof exarnination, Accordingly, a sunscreen product that has both high transparency and water mesistance can be successfully formulated using the new graft copolymer as a dispersing agents.

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Surveys conducted in many nations suggest that up to 50% of cosmetic users believe they have sensitive skin and products specifically designed for this skin type have become an important cosmetic category. In developing such products, objective assessment of the degree and type of sensitivity is desirable. Unfortunately, currently available methods, including measurements of trans-epidermal water loss (TEWL) and lactic acid stinging tests, do not correlate well with self-assessed sensitivity and cannot be used to identify persons who are more prone to develop adverse skin reactions than other users. A simple, more reliable non-invasive method for detecting skin sensitivity is needed. In developing such a method, it is necessary to understand the exact meaning of “sensitivity” as used by consumers to describe their skin condition. Our extensive surveys of 130 subjects, conducted over a one-year period and taking into consideration seasonal variations, revealed that the meaning varies somewhat among individuals, but that there is a consensus on specific skin conditions to which they refer when they report having sensitive skin, These conditions include tendencies for their skin to itch, develop redness and become dry and flaky. Our investigations revealed that the development of skin sensitivity is often related to a reduction in the barrier function of the stratum corneum, and thus a method could be developed using certain biophysical properties of corneocytes to predict skin sensitivity. Our search for such an objectively measurable sensitivity index led us to the discovery that a certain parameter of the average projected area of corneocytes obtained via tape stripping at a specific area of facial skin can be used for this purpose. Our new method, called APAc, is more reliable and convenient in predicting self-assessed skin sensitivity than are TEWL or lactic acid stinging tests.

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