Yoshimasa Miura

Algorithm for in vitro Sun Protection Factor Based on Transmission Spectrum Measurement with Concomitant Evaluation of Photostability

In thein vitro evaluation of Sun Protection Factor (SPF), the photostability of the ultraviolet (UV) filters can have a major impact, especially for high‐SPF formulations, but is generally not taken into consideration. In this study, we present a UV transmission spectrum measurement system utilizing a high‐sensitivity UV photomultiplier tube with concomitant evaluation of photostability. We have developed an algorithm to estimate SPF in vitro by converting the amount of UV light transmission through the sunscreen layer into cumulative relative erythema effectiveness to obtain one minimal erythema dose. Thus, the algorithm uses the same endpoint as in vivo SPF methods, but with a photomultiplier tube as the detector instead of skin. The values obtained showed an excellent correlation with in vivo SPF values, even for high‐SPF sunscreens exceeding SPF 50. This method should be suitable as an in vitro SPF testing method for regulatory purposes.

Response to Comments by Sayre, Dowdy and Stanfield on our Article Entitled “Algorithm for in vitro Sun Protection Factor Based on Transmission Spectrum Measurement with Concomitant Evaluation of Photostability.”Photochem. Photobiol. (2008)

We appreciate the interest shown by Drs. Sayre, Dowdy and Stanfield in our article ‘‘Algorithm for in vitro Sun Protection Factor Based on Transmission Spectrum Measurement with Concomitant Evaluation of Photostability,’’ published in the November–December 2008 issue (volume 84) of Photochemistry and Photobiology (1), and their recognition of the importance of in vitro SPF measurement taking photostability into account. Our response to their comment, ‘‘In-Vitro Sunscreen Transmittance with Concomitant Evaluation of Photostability: Evolution of a Method’’ (2), is as follows. First, we are pleased to note that they agree with our comment that it would be preferable to use an application dose of 2.00 mg cm, as in in vivo SPF measurement, stating that ‘‘the application amount for in vitro sunscreen evaluations should be 2 mg cm as used in the human SPF test, because photostability testing on thinner layers of sunscreen product, as many methods have utilized, may underestimate product photostability of the thicker films associated with human SPF testing.’’ Actually, we have already reported that in vitro SPF evaluation among various types of formulation with the application dose of 2 mg cm shows a good correlation with in vivo SPF value, in the IFSCC Congress 2009 in Barcelona (3). We think this good result is at least partly due to the development of the new substrate that mimics skin well; its roughness shows a value similar to that of back skin, and samples at this application dose can be uniformly applied. Regarding the use of relative intensity (a.u.), we also agree with their comment (in ‘‘Predicting SPF During Photodegradation’’) that ‘‘The resulting spectra should be transmitted irradiance in W cm nm, preferably plotted on a logarithmic y-axis scale to illustrate system dynamic range and noise equivalent irradiance detection limit.’’ However, at this point, we used relative intensity (a.u.). because in vitro SPF can be simply estimated from the relative value of a sample with respect to the reference. Calibration of the system to take account of the quantum efficiencies of detector and grating of the double monochromator, gain and so on would allow us to convert relative values to approximate absolute values. Sayre et al. suggested in the section ‘‘Key Information Needed’’ that further information was required about various aspects of the study, and we are happy to provide that as follows:

Design and Development of an Innovative Hybrid Powder Based on a Computer Simulation and Its Application to Base Make Up Products

コンピューターシミュレーションによる新たな粉体開発によって, 従来にないきめ細かな質感を有するファンデーションの開発を行った。女性が羨望する乳幼児のきめ細かな肌の光学特性を測定・解析することで粉体の光学的な構造設計を行った。光学特性の最適化を図るためにシミュレーションの計算手法にMaxwellの微分方程式を差分化し時間領域で解くFDTD (finite differential time domain) 法を用いた。光学的な理想構造に基づいた複合粉体の合成には薄片状基板に硫酸バリウムの結晶を微細球状に被覆する形態制御被覆技術を用いた。開発した複合粉体の光学特性は一次粒子レベルで高い拡散特性を有していることが確認され, 複合粉体を配合したファンデーションは毛穴や小じわ, しみ・そばかすなどを均一に補正し, 従来にない繊細な反射特性によるきめ細かな質感を演出していた。

Design and development of an innovative hybrid powder based on a computer simulation and its application to foundation makeup products

An innovative hybrid powder prepared using computer simulation allowed development of a new foundation having a fine, smooth texture that has never been achieved before. The optical structure/design of the powder was based on the results of measurements and analyses conducted on the optical characteristics of a babys delicate skin, which is the envy of many women. To obtain the optimal optical characteristics, the finite differential time domain (FDTD) method for solving Maxwells differential equation by difference and time domain was applied to the computer simulation method. For synthesis of the hybrid powder based on the optical model, a proprietary shape regulation coating technology was used in which flaky substrates were coated with microspherical forms of barium sulfate crystals. The hybrid powder developed exhibited optical characteristics that showed a significant diffusion characteristic in the visible light region. The foundation containing this powder could conceal pores, small wrinkles, freckles, and age spots and owing to its microscopic reflection characteristics provided a fine, smooth texture that has never before been available with a conventional foundation.

Study on Radiation Transfer in Human Skin for Cosmetics

In order to design cosmetics producing the optical properties that are required for a beautiful skin, the radiation transfer in the skin has been numerically investigated by a Monte Carlo method, and the effects of skin texture and cosmetics on the radiation transfer have been empirically investigated using an artificial skin with a skin texture. The numerical analysis showed that the total internal reflection suppresses not a small portion of radiation going out through the skin surface. And, the experimental study revealed that skin texture and cosmetics do not only diffusely reflect the incoming radiation, but also lead the internally reflected radiation to the outside of the skin.