Method for evaluating transparency of skin

Abstract

The present invention relates to a method for evaluating the transparency of skin, the method comprising irradiating evaluation skin with irradiation light and quantifying, by simulation, the amount of irradiation light that has reached a specific penetration depth. The simulation is based on the intensity of reflected light and uses the attenuation coefficient of the skin and the albedo of the skin.

Description

Method for evaluating skin transparency

[0001] The present invention relates to a method for evaluating skin transparency.

[0002] Since transparent skin gives an impression of youthfulness and health, skin transparency is an aesthetic element sought by many people. In previous studies, reports on the relationship between the water content of the stratum corneum, skin blood flow, or melanin amount and skin transparency have been central (for example, Non-Patent Documents 1 to 3).

[0003] Masahiko Ooe et al., “Influence of Hydration for Optical Properties of Stratum Corneum”, J. Soc. Cosmet. Chem. Japan Vol. 35, No. 4 2001. Yasuo Kaneda, “What is dullness - Regarding its causes and definitions”, Fragrance Journal, 2, 9 - 16 (1996) Marin Q et al., “Analysis of correlation and construction of a predictive model of skin transparency using parameters from digital images of the face.”, Skin Res Technol. 2022 Jul;28(4):582 - 595.

[0004] However, in the visual aesthetic evaluation, the above measured values did not necessarily correlate with skin transparency.

[0005] The present invention has been made in view of the above circumstances, and an object thereof is to provide a method for evaluating skin transparency that enables an evaluation closer to the visual impression.

[0006] The present invention includes, for example, the following inventions: [1] A method for evaluating skin transparency, comprising irradiating a target skin with irradiation light and quantifying the amount of irradiation light that reaches a specific penetration depth by simulation, wherein the simulation is a simulation based on reflected light intensity using the attenuation coefficient of the skin and the albedo of the skin. [2] The method according to [1], wherein the specific penetration depth is 2.0 mm or less from the surface of the skin. [3] The method according to [1] or [2], wherein the specific penetration depth is 0.1 mm or more and 0.8 mm or less from the surface of the skin. [4] The method according to any one of [1] to [3], wherein the skin transparency is the transparency of the skin as seen by the eye. [5] The method according to any one of [1] to [4], wherein the irradiation light includes a striped pattern having irradiated and unirradiated areas on the skin. [6] The method according to [5], wherein the reflected light intensity used in the simulation is determined based on the lowest value in the luminance value distribution of reflected light along the longitudinal direction of the irradiation area. [7] A system comprising: a light irradiation means for irradiating an object to be measured with light containing light of a specific wavelength; a slit mask provided between the object to be measured and the light irradiation means, which forms a light-irradiated area and a light-non-irradiated area on the object to be measured; and a light-receiving means for receiving reflected light from the object to be measured. [8] The system according to [7], wherein the light irradiation means comprises a light source and a wavelength selection mechanism. [9] The system according to [7] or [8], wherein the light of a specific wavelength is visible wavelength light.

[10] The system according to any one of [7] to [9], wherein the light of a specific wavelength is light in the wavelength range of 360 nm to 830 nm.

[11] The system according to any one of [7] to

[10] , which is a system for use in a method for evaluating the transparency of skin.

[0007] According to the present invention, it is possible to provide a method for evaluating skin transparency that allows for an evaluation closer to the visual impression.

[0008] Figure 3 is a schematic diagram of a system according to one embodiment. Figure 4(A) is a schematic diagram of a system according to one embodiment. Figure 5(A) is a schematic diagram of a system according to one embodiment. Figure 5(B) is a schematic diagram of a system according to one embodiment. Figure 3 is a schematic diagram of a system according to one embodiment. Figure 4(A) is a schematic diagram of a system according to one embodiment. Figure 5(B) is a schematic diagram of a system according to one embodiment. Figure 5(A) is a schematic diagram of a system according to one embodiment. Figure 5(B) is a schematic diagram of a system according to one embodiment. Figure 3 is a schematic diagram of a system according to one embodiment. Figure 5(A) is a schematic diagram of a system according to one embodiment. Figure 5(B) is a schematic diagram of a system according to one embodiment. Figure 5(B) is a schematic diagram of a system according to one embodiment. Figure 3 is a schematic diagram of a system according to one embodiment. Figure 5(A) is a schematic diagram of a system according to one embodiment. Figure 5(B) is a schematic diagram of a system according to one embodiment. Figure 5(A) is a schematic diagram of a system according to one embodiment. Figure 5(B) is a schematic diagram of a system according to one embodiment. This is an explanatory diagram of a method for plotting the minimum value in the brightness distribution of reflected light along the X direction for each pixel in the Y direction (each Y pixel) using the acquired measurement image (Figure 3(B)). This graph shows the result of plotting the minimum value in the brightness distribution of reflected light along the X direction for each pixel in the Y direction (each Y pixel) using the image in Figure 3(B).

[0009] The following describes in detail embodiments for carrying out the present invention. However, the present invention is not limited to the following embodiments.

[0010] [Method for evaluating skin transparency] The method for evaluating skin transparency according to this embodiment includes irradiating the target skin with light and quantifying the amount of light that reaches a specific penetration depth by simulation. Here, the above simulation is a simulation based on reflected light intensity using the skin attenuation coefficient and the skin albedo.

[0011] In this specification, "skin transparency" refers to the transparency of the skin as perceived by the human eye, and is expressed, for example, as "a state in which the skin appears clear and transparent without any cloudiness." As shown in this embodiment, we found that there is a correlation between the score obtained from the sensory evaluation of "visual transparency" by women in their 20s and 30s and the numerical value obtained by quantifying the amount of irradiated light irradiated onto the target skin that reached a specific penetration depth. Therefore, according to the method of this embodiment, it is possible to evaluate skin transparency that is closer to the visual impression (visual perception). Specifically, skin transparency may refer to, for example, the transparency of the skin as perceived by the eye.

[0012] (Irradiation with light) The subject to which the light is irradiated is not particularly limited as long as it is a subject for which it is desired to evaluate the transparency of the skin, but it may be a human being.

[0013] The skin to be irradiated with the light can be any part of the body that can be irradiated with the light, but it may be skin such as the cheeks, forehead, around the eyes, forearms, upper arms, back of the hands, neck, back, and feet, with the skin of the cheek being preferred.

[0014] The light irradiated onto the target skin may, for example, be light in the wavelength range of 360 nm to 830 nm, 370 nm to 820 nm, 380 nm to 810 nm, 390 nm to 800 nm, 400 nm to 800 nm, 420 nm to 750 nm, 450 nm to 700 nm, or 480 nm to 650 nm. Alternatively, the light irradiated onto the target skin may be light in the wavelength range of 360 nm to 830 nm (visible light).

[0015] The irradiated light may include a striped pattern on the skin having irradiated and non-irradiated areas. The widths of the irradiated and non-irradiated areas may be, for example, 0.01 mm to 10 mm, 0.1 mm to 8 mm, 0.5 mm to 6 mm, 1 mm to 5 mm, 1 mm to 4 mm, 1 mm to 3 mm, 1 mm to 2 mm, or 1 mm, respectively. The widths of the irradiated and non-irradiated areas may be the same or different.

[0016] One method for irradiating a target area with light containing a striped pattern is to use a slit-row mask to irradiate the target skin with light.

[0017] The angle at which the light is irradiated onto the skin is not particularly limited, but may be, for example, 10 degrees to 50 degrees, 15 degrees to 45 degrees, 20 degrees to 40 degrees, 25 degrees to 35 degrees, or 30 degrees.

[0018] (Quantification of the amount of irradiated light that reaches a specific penetration depth) The quantity of irradiated light that reaches a specific penetration depth is quantified by a simulation based on reflected light intensity using the skin attenuation coefficient and the skin albedo. The method according to this embodiment may further include obtaining reflected light intensity data, and obtaining the skin attenuation coefficient and the skin albedo from the reflected light intensity data in order to perform the simulation.

[0019] <Reflected Light Intensity Data> Reflected light intensity data can be obtained by irradiating the target skin with light and detecting the reflected light. The reflected light intensity data may be obtained using a post-spectroscopic system or a pre-spectroscopic system, and it is preferable to obtain it using a pre-spectroscopic system. The reflected light intensity data may be, for example, spatial distribution data of reflected light intensity. The spatial distribution data of reflected light intensity may be, for example, data showing the relationship between the position of the skin irradiated with light and the reflected light intensity from that skin. The reflected light intensity from the skin may be, for example, the vertical reflected light intensity obtained when irradiated at an arbitrary irradiation angle. The reflected light intensity from the skin may also be, for example, the reflectance intensity non-dimensionalized using radiant energy flux.

[0020] If the spatial distribution data of reflected light intensity is obtained using a pre-spectroscopic system, and the irradiated light includes a striped pattern with irradiated and non-irradiated areas on the skin, the reflected light intensity may be determined based on the mean, median, or minimum value of the luminance value distribution of the reflected light along the longitudinal direction of the irradiated area, and it is preferable that it be determined based on the minimum value from the viewpoint of more accurate evaluation. Alternatively, if the spatial distribution data of reflected light intensity is obtained using a pre-spectroscopic system, and the irradiated light includes a striped pattern with irradiated and non-irradiated areas on the skin, the data may be obtained by plotting the minimum value of the luminance value distribution of the reflected light along the longitudinal direction of the irradiated area for each direction perpendicular to the longitudinal direction of the irradiated area. The pre-spectroscopic system may be the system according to this embodiment described later.

[0021] <Skin Attenuation Coefficient and Skin Albedo> The skin attenuation coefficient is a numerical value that indicates how much the intensity of light decreases due to absorption and scattering as light propagates through the skin. Skin albedo is a numerical value that indicates the ratio of the decrease in light intensity due to scattering to the decrease in light intensity due to absorption and scattering as light propagates through the skin. These are one of the optical properties of the skin.

[0022] The attenuation coefficient and albedo of the skin can be obtained, for example, by inverse analysis of reflected light intensity data. Examples of inverse analysis include inverse analysis using the Monte Carlo method, inverse analysis using the light diffusion equation with diffusion approximation, and inverse analysis using the isotropic scattering approximation. To perform inverse analysis and optical simulation more accurately, it is preferable to use the Monte Carlo method.

[0023] When obtaining the skin attenuation coefficient and skin albedo by inverse analysis, for example, the equation represented by the following equation (1) may be used for the inverse analysis.

[0024] [In formula (1), I represents the intensity of light, Ω represents the unit vector representing the direction of light propagation, s represents the distance in the propagation direction, β represents the attenuation coefficient, ω represents the albedo, and p represents the scattering phase function.]

[0025] More specifically, a method for obtaining the skin attenuation coefficient and skin albedo by inverse analysis is as follows: The reflected light intensity data obtained by actual measurement is compared with the reflected light intensity data obtained by simulation, and the skin attenuation coefficient and skin albedo are estimated and determined so that the measured reflected light intensity data and the simulated reflected light intensity data show the best agreement.

[0026] If the irradiated light contains a striped pattern, and the reflected light intensity data shows the relationship between the position of the irradiated skin and the reflected light intensity from that skin, the attenuation coefficient and albedo of the skin can be estimated using the reflected spatial profiling method. In this case, the albedo of the skin can be estimated from the average intensity calculated from the measured reflected light intensity using the following formula (2). The attenuation coefficient can be estimated using the estimated albedo, and can be calculated based on the average deviation calculated from the measured reflected light intensity using the following formula (3). In estimating the attenuation coefficient and albedo of the skin, for example, the scattering phase functions shown in the following formulas (4) and (5) may be used.

[0027] [In formula (2), the underlined i represents the average intensity, y represents the position of the skin irradiated with the light, and L represents the distance between adjacent irradiated areas in the light field.]

[0028] [In formula (3), the underlined σ represents the average deviation, the underlined i represents the average intensity, y represents the position of the skin irradiated with the light, and L represents the distance between adjacent irradiated areas in the light field.]

[0029] [In equation (4), θ represents the scattering angle, and g represents the asymmetry factor.]

[0030] [In equation (5), θ represents the scattering angle, and g represents the asymmetry factor.]

[0031] The above-mentioned methods for estimating the skin attenuation coefficient and skin albedo can be carried out more specifically according to the method described in, for example, Biomed Opt Express. 2019 Jul 2;10(8):3747-3759.

[0032] <Simulation of the amount of irradiated light reaching a specific penetration depth> The amount of irradiated light reaching a specific penetration depth can be quantified, for example, by simulating the propagation of light within the skin based on reflected light intensity data using the skin attenuation coefficient and skin albedo, and then statistically analyzing the number of photons that reached the specific penetration depth from the simulation results. This simulation and statistical analysis can be performed, for example, by the Monte Carlo method.

[0033] The above simulations and statistical analyses using the Monte Carlo method can be performed, for example, by referring to the description in Optics Vol. 34 No. 11 (2005), pp. 562-567.

[0034] The "specific penetration depth" in the amount of irradiated light that reaches a specific penetration depth may be, for example, 2.0 mm or less from the skin surface, 1.5 mm or less from the skin surface, 1.0 mm or less from the skin surface, or 0.8 mm or less from the skin surface, and may also be 0.01 mm or more, 0.05 mm or more, or 0.1 mm or more from the skin surface. The amount of irradiated light that reaches a specific penetration depth may be one or more selected from the group consisting of, for example, the amount of irradiated light that reaches the stratum corneum of the skin, the amount of irradiated light that reaches the epidermis of the skin, and the amount of irradiated light that reaches the dermis of the skin.

[0035] The stratum corneum of the skin may be, for example, a portion less than 0.015 mm from the surface of the skin, the epidermis of the skin may be, for example, a portion between 0.015 mm and less than 0.1 mm from the surface of the skin, and the dermis of the skin may be, for example, a portion between 0.1 mm and 0.8 mm from the surface of the skin.

[0036] (Comparison of the amount of irradiated light reaching a specific penetration depth) The evaluation method according to this embodiment may further include comparing the amount of irradiated light reaching a specific penetration depth of a comparison target. The amount of irradiated light reaching a specific penetration depth in both of the comparison targets is the same amount of irradiated light reaching a specific penetration depth. The amount of irradiated light reaching a specific penetration depth in the comparison target may be one or more.

[0037] The amount of irradiated light that reaches a specific penetration depth for comparison may be, for example, the average value of the amount of irradiated light that reaches a specific penetration depth, which is quantified in the same way as for each subject, for multiple subjects judged to have high skin transparency. This serves as a reference value, allowing for an absolute evaluation of skin transparency. The number of subjects judged to have high skin transparency is preferably large, for example, five or more, ten or more, fifteen or more, or twenty or more.

[0038] The amount of irradiated light that reaches a specific penetration depth in the comparison target may be, for example, a numerical value representing the amount of irradiated light that reaches a specific penetration depth in one or more other targets, calculated in the same manner as the target. This allows for a relative evaluation of skin transparency by comparing the amount of irradiated light that reaches a specific penetration depth with one or more other targets.

[0039] [System] The system according to this embodiment comprises a light irradiation means for irradiating an object to be measured with light containing a specific wavelength, a slit mask provided between the object to be measured and the light irradiation means to form a light-irradiated area and a light-non-irradiated area on the object to be measured, and a light-receiving means for receiving reflected light from the object to be measured. The system according to this embodiment is a system that irradiates an object to be measured with light containing a specific wavelength, and is a pre-spectroscopic system. A post-spectroscopic system is a system in which a spectroscopic optical element or the like is placed between the object to be measured and the light-receiving means.

[0040] The system according to this embodiment is not particularly limited. For example, it may be a system for evaluating the state of the surface layer of a measurement object. More specifically, it may be a system for evaluating the transparency of a measurement object (skin), a system for evaluating the surface structure (fine irregularities and texture) of a measurement object (skin), a system for evaluating skin roughness of a subject, etc.

[0041] The system according to this embodiment will be described with reference to FIG. 1. FIG. 1 is a schematic diagram of a system 1 according to an embodiment. The system 1 includes a light irradiation unit 11, a slit mask 12, and a light receiving unit 13. FIG. 2 is an image of a system according to an embodiment used in Test Examples 2 to 3.

[0042] The light irradiation unit 11 may be a light irradiation device. The light irradiation unit 11 may also include a light source 111 (e.g., a light source device) and a wavelength selection mechanism 112 (e.g., a wavelength selection device). In this case, light irradiated from the light source 111 is selected by the wavelength selection mechanism 112 to have a specific wavelength range, and the light of the specific wavelength range is irradiated onto the measurement object O. The light irradiation unit 11 may include a light source 111, a collimator lens 113, a wavelength selection mechanism 112, and a projection lens 114. The light source 111, the collimator lens 113, and the wavelength selection mechanism 112 may be arranged in this order, and the projection lens 114 is arranged between the slit mask 12 and the measurement object O. In this case, the light irradiated from the light source 111 is made parallel by the collimator lens 113 and condensed onto the wavelength selection mechanism 112. The condensed light passes through the wavelength selection mechanism 112 after a specific wavelength range of light is selected. Thereafter, the light of the specific wavelength range passes through the slit mask 12 and is irradiated by the projection lens 114 to form a light irradiation part and a non-light irradiation part in the measurement area on the surface of the measurement object O.

[0043] The light source 111 is not particularly limited. For example, a light source device such as an LED lamp, a halogen lamp, a metal halide lamp, a xenon lamp, an incandescent bulb, a laser light source, an ultraviolet lamp, etc. can be used. The projection angle θ of the incident light irradiated from the light source 111 is not particularly limited and can be appropriately selected by those skilled in the art according to the refractive index of the measurement object, etc.

[0044] Light of a specific wavelength may be, for example, light in a wavelength range of 360 nm or more and 830 nm or less, 370 nm or more and 820 nm or less, 380 nm or more and 810 nm or less, 390 nm or more and 800 nm or less, 400 nm or more and 800 nm or less, 420 nm or more and 750 nm or less, 450 nm or more and 700 nm or less, 480 nm or more and 650 nm or less. Further, the light of a specific wavelength may be light (visible light) in a wavelength range of 360 nm or more and 830 nm or less.

[0045] The wavelength selection mechanism 112 is not particularly limited as long as it can select and pass incident light L1 as light in a specific wavelength range. For example, wavelength selection devices such as one or more types of band-pass filters and monochromators can be used.

[0046] The slit shape of the slit mask 12 is usually a quadrilateral, preferably a rectangle. Also, the slit width of the slit mask 12 is not particularly limited and can be appropriately selected according to the desired measurement area width in the measurement object, the material of the measurement object, etc. Specifically, it may be the same as the width of the above irradiation part and the non-irradiation part. Further, the number of slits of the slit mask 12 is not particularly limited and is, for example, one or more.

[0047] The light receiving means 13 may be a light receiving device. The light receiving means 13 is means for receiving scattered light L2 in which light incident on the measurement object O is scattered inside the measurement object and specular reflection light L3 in which light incident on the measurement object O is specularly reflected, or the above L2. The light receiving means 13 is preferably means for receiving the above L2 (means for receiving only the above L2 and not receiving the above L3).

[0048] The arrangement of the light receiving means 13 is not particularly limited, but it is preferably arranged at a position where the specular reflection light L3 is not received. That is, it is preferable that the angle formed by the tangent at the intersection of the straight line passing through the center of the light receiving means 13 and the measurement object is smaller than 2θ (the angle obtained by doubling the projection angle θ of the incident light).

[0049] The light-receiving means 13 is not particularly limited as long as it can receive reflected light (scattered light and specularly reflected light) that is reflected by the object to be measured after light incident on the object to be measured O has been reflected by the object to be measured. For example, a light-receiving device such as a CCD camera or a CMOS camera can be used.

[0050] The object to be measured may be the skin being evaluated. If the object to be measured is skin, it may be skin from the cheeks, forehead, around the eyes, forearms, upper arms, back of the hands, neck, back, and feet, but skin from the cheeks is preferred.

[0051] When the system according to this embodiment is used as a system for evaluating the transparency of skin according to this embodiment, the evaluation of the transparency of the skin can be performed by obtaining reflected light intensity data using an image acquired based on the light receiving means in the system according to this embodiment. The reflected light intensity data may be, for example, obtained by plotting the lowest value in the brightness value distribution of reflected light along the longitudinal direction of the slit of the slit of the slit mask (hereinafter also referred to as the X direction) for each pixel (each Y pixel) perpendicular to the X direction (each Y direction). Specifically, it may be as shown in Test Example 2 in the embodiments described later.

[0052] The present invention will be described more specifically below based on examples. However, the present invention is not limited to the following examples.

[0053] (Test Example 1) For various skin measurement values, the following evaluation was conducted to determine which skin measurement value correlated most highly with the visual assessment of skin transparency.

[0054] <Participants> 24 men and women aged 20 to 50

[0055] <Test Method> (1) Irradiated light passing through a row of slits was applied to the cheeks of subjects after washing their faces, so that the irradiated and non-irradiated areas alternated in a striped pattern on the skin. The amount of irradiated light that reached the stratum corneum, epidermis, and dermis was simulated under the following conditions based on the reflected light intensity data. (2) Conditional imaging of the subject's cheek was performed using VISIA Evolution (manufactured by Canfield Scientific), and moisture content was measured using SKICON-EX200 (manufactured by Yayoi Corporation), and sebum content was measured using Sebumeter SM815 (manufactured by Courage + Khazaka). (3) For the VISIA images of the subject's cheek, a paired evaluation was conducted with 10 women in their 20s and 30s as evaluators, and the following "visual transparency" scores were assigned. The correlation between the "visual transparency" score based on the evaluations in (4) and (3) and the scores obtained by ranking the measurement results in (1) and (2) was examined. The individual measurement values ​​and scores are shown in Tables 1 and 2, and the correlation results are shown in Table 3. In Table 3, "Amount of light reached (total)" is the sum of the amounts of light that reached the stratum corneum, epidermis, and dermis, respectively, and represents the amount of light that reached the inside of the skin.

[0056] <Simulation Conditions> ・Wavelength of light: 550 nm ・Depth of light penetration: Stratum corneum < 0.015 mm, Epidermis 0.015 mm << 0.1 mm, Dermis 0.1 mm << 0.8 mm

[0057] <Simulation Method> The spatial distribution data of reflected light intensity obtained in (1) was used to determine the attenuation coefficient of the skin and the albedo of the skin by inverse analysis using the Monte Carlo method described in non-patent literature (Biomeed Opt Express. 2019 Jul 2;10(8):3747-3759.). The equation represented by the following formula (1) was also used. The spatial distribution data is data showing the relationship between the position of the skin irradiated with light and the reflected light intensity from that skin. The reflected light intensity from the skin is the vertical reflected light intensity obtained when the light is irradiated at an irradiation angle of 30 degrees, and is represented by the following formula (6) which is dimensionless using the radiant energy flux. ＊ (θ = 0, y). i is expressed by the following formula (6). ＊(θ = 0, y) is based on the definition of bidirectional reflectance shown in the non-patent literature (Brewster, MQ, Thermal Radiative Transfer and Properties, (1992), p. 42, Wiley Interscience, New York).

[0058] [In formula (1), I represents the intensity of light, Ω represents the unit vector representing the direction of light propagation, s represents the distance in the propagation direction, β represents the attenuation coefficient, ω represents the albedo, and p represents the scattering phase function.]

[0059] Specifically, the albedo of the skin was estimated from the average intensity calculated from the measured reflected light intensity using the following formula (2). The attenuation coefficient was calculated based on the estimated albedo and the average deviation calculated from the measured reflected light intensity using the following formula (3). In addition, the scattering phase function shown in the following formulas (4) and (5) was used.

[0060] [In formula (2), the underlined i represents the average intensity, y represents the position of the skin irradiated with the light, and L represents the distance between adjacent irradiated areas in the light field.]

[0061] [In formula (3), the underlined σ represents the average deviation, the underlined i represents the average intensity, y represents the position of the skin irradiated with the light, and L represents the distance between adjacent irradiated areas in the light field.]

[0062] [In equation (4), θ represents the scattering angle, and g represents the asymmetry factor.]

[0063] [In equation (5), θ represents the scattering angle, and g represents the asymmetry factor.]

[0064] [In equation (6), i (θ = 0, y) represents the vertical reflected light intensity obtained when irradiated at an irradiation angle of 30 degrees, q represents the radiant energy flux, i ＊(θ = 0, y) represents the above reflection intensity, non-dimensionalized using the radiant energy flux q of the irradiated area.

[0065] After determining the attenuation coefficient and albedo of the skin, the propagation of light within the skin was simulated based on reflected light intensity data, using the optical properties of the skin and the depth of light penetration. The amount of irradiated light reaching the penetration depths of the stratum corneum, epidermis, and dermis was quantified by statistically analyzing the number of photons reaching specific penetration depths from the simulation results. This simulation and statistical analysis were performed using the Monte Carlo method.

[0066] <"Visual Transparency" Score> The "Visual Transparency" score was assigned using Scheffé's pairwise comparison method (a modification of Nakaya's method). That is, the order of comparison was not considered, and each evaluator compared all combinations of cheek images once. Images of cheeks selected in a random order were displayed side by side, and their visual transparency was evaluated on a 5-point scale (left is very (-2), left is somewhat (-1), same (0), right is somewhat (1), right is very (2)). The average preference was calculated from the evaluation results of all combinations based on Scheffé's pairwise comparison method, and the standardized value was used as the "Visual Transparency" score.

[0067] <Method for confirming correlation> The correlation between the "visual transparency" score obtained from the evaluation in (3) and the scores obtained by ranking the measurement results in (1) and (2) was verified using the "multivariate correlation" function of the statistical software JMP.

[0068] <Results> Previous studies had evaluated the correlation between skin moisture content and skin transparency. As shown in Table 3, skin transparency showed a stronger correlation with the amount of irradiated light that reached the inside of the skin, especially the dermis (penetration depth: 0.1 mm to 0.8 mm), than with the stratum corneum moisture content.

[0069]

[0070]

[0071]

[0072] (Test Example 2) A system (pre-spectroscopy system) as shown in Figure 2 was constructed, and the objects to be measured in Figure 2 were the cheeks of two subjects (Example 1 and Example 2) after washing their faces. Subject 1 was irradiated with light of a wavelength of 500 nm, and subject 2 was irradiated with light of a wavelength of 550 nm. After that, the cheeks of each subject were photographed. The measurement images are shown in Figure 3.

[0073] By processing the measurement images of Example 1 and Example 2 shown in Figure 3 with an image analysis program and converting them into numerical data, we obtained luminance value distribution data (spatial distribution data of reflected light intensity) of reflected light along the longitudinal direction of the slit of the slit mask (hereinafter referred to as the X direction). The results are shown in Figure 4. Figure 4(A) is the luminance value distribution data of the subject in Example 1, and Figure 4(B) is the luminance value distribution data of the subject in Example 2. Similarly, we also obtained the luminance value distribution of reflected light along the direction perpendicular to the X direction (hereinafter referred to as the Y direction). The results are shown in Figure 5. Figure 5(A) is the luminance value distribution data of the subject in Example 1, and Figure 5(B) is the luminance value distribution data of the subject in Example 2.

[0074] As shown in Figures 4-5, when luminance value distribution data of reflected light was obtained using the system shown in Figure 2, the degree of variation in luminance values ​​differed among subjects, and the subject in Example 2, in particular, showed a large variation in luminance values. As can be seen from these results, it was considered that the luminance value distribution data is greatly influenced by the surface structure of the skin (fine irregularities and texture). When using a post-spectroscopy system, the spectrometer, due to its structure, performs spectral processing on light that has passed through an incident slit having a predetermined area (for example, a slit with a width of several mm). In this spectral processing, the reflected light received from the incident slit is spatially averaged and then decomposed into wavelength components. As a result, the obtained measurement value becomes the average light intensity of the entire region at a specific wavelength, and spatial distribution information is lost (for example, the measurement image will be like that shown in Figure 6(A)). In contrast, when using a pre-spectroscopy system, the spatial averaging process described above is not involved. Therefore, it becomes possible to acquire the brightness distribution of the light pattern formed on the skin surface as two-dimensional spatial information (surface information) (for example, the measured image will be like the one shown in Figure 6(B). Figure 6(B) is a measured image obtained by irradiating the object to be measured with light of a wavelength of 550 nm). From this, it was considered that the above-mentioned variation in brightness values ​​could be captured when using a prespectroscopy system. Furthermore, since the above-mentioned brightness value distribution data is greatly influenced by the surface structure of the skin (fine irregularities and texture), it is considered that the system of the present invention can also be used to evaluate the roughness of the target skin and the surface structure of the skin (fine irregularities and texture).

[0075] Regarding the variation in luminance values, considering the principle of light propagation, it is thought that using data with the least reflection at the skin surface interface will allow for a more accurate evaluation of data within the skin. Therefore, the inventors considered that, taking advantage of the fact that information on the variation in luminance values ​​can be obtained using a pre-spectroscopic system, it would be best to use the data of the lowest value in the luminance value distribution of reflected light along the X direction as reflected light intensity data for estimating the attenuation coefficient and albedo of the skin, and for simulations based on reflected light intensity. As shown in Figure 7, using the measurement image (Figure 3(B)) acquired from the subject in Example 2, the lowest value in the luminance value distribution of reflected light along the X direction was plotted for each pixel in the Y direction (each Y pixel). The results are shown in Figure 8.

[0076] Based on the reflected light intensity data shown in Figure 8, and similar to Test Example 1, simulating the amount of irradiated light that reached the stratum corneum, epidermis, and dermis suggests that the amount of irradiated light that reached the interior of the skin correlates more strongly with skin transparency.

[0077] (Test Example 3) For various skin measurement values, the following evaluation was conducted to determine which skin measurement value correlated most highly with the visual assessment of skin transparency.

[0078] <Subjects> 22 men and women aged 20 to 50, as shown in Table 4.

[0079]

[0080] <Test Method> (1) Using the system shown in Figure 2 (prespectival spectroscopic system), the irradiated light that passed through the slit row was shone onto the cheeks of subjects after washing their faces, and the amount of irradiated light that reached the stratum corneum, epidermis, and dermis was simulated under the following conditions based on the reflected light intensity data. Three types of bandpass filters (500 nm, 550 nm, 600 nm: transmission wavelength band 10 nm) were used for the irradiated light. As with Test Example 2, the reflected light intensity data was obtained by plotting the lowest value in the brightness value distribution of reflected light along the X direction for each pixel in the Y direction (each Y pixel) using the acquired measurement image. The simulation conditions are as described below, and the simulation method is the same as in Test Example 1. (2) The cheeks of the subjects were photographed using VISIA Evolution (manufactured by Canfield Scientific), and the amount of stratum corneum moisture was measured using SKICON-EX200 (manufactured by Yayoi Corporation), and the amount of sebum was measured using Sebumeter SM815 (manufactured by Courage + Khazaka). (3) The VISIA images of the subjects' cheeks were evaluated in a paired evaluation by 10 women in their 20s and 30s, and a "visual transparency" score was assigned, similar to Test Example 1. (4) Similar to Test Example 1, the correlation between the "visual transparency" score from the evaluation in (3) and the scores obtained by ranking the measurement results in (1) and (2) was confirmed.

[0081] <Simulation Conditions> ・Light Wavelength: 500nm, 550nm, 600nm ・Light Penetration Depth: Stratum Corneum <0.015mm, Epidermis 0.015mm << 0.1mm, Dermis 0.1mm << 0.8mm

[0082] <Method for confirming correlation> The correlation between the "visual transparency" score from the evaluation in (3) and the scores obtained by ranking the measurement results in (1), or the stratum corneum moisture content and sebum content measured in (2), was confirmed by calculating Spearman's rank correlation coefficient. The measured values ​​and scores are shown in Tables 5 to 7, and the correlation results are shown in Tables 8 to 16. In the tables, rho indicates Spearman's correlation coefficient. When Rho is 0, the two variables are completely unrelated, and the closer it is to 1 or -1, the stronger the relationship between the variables. Also, Table 17 shows the results of the rank correlation coefficients for each Spearman.

[0083] <Results> As shown in Tables 8-16, skin transparency showed a strong correlation with the amount of irradiated light that reached the stratum corneum (penetration depth: ~0.015 mm) or the epidermis (penetration depth: ~0.1 mm), and it was suggested that there was a particularly strong correlation with the amount of irradiated light that reached the dermis (penetration depth: ~0.8 mm). Furthermore, similar results were obtained regardless of the wavelength of light irradiated. As shown in Table 17, previous studies evaluated the correlation between skin moisture content and skin transparency, but this study suggests that simulating the amount of light that penetrates the interior of the skin shows a stronger correlation with the visual evaluation of transparency.

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[0097] 1...System, 11...Light irradiation means, 12...Slit mask, 13...Light receiving means, 111...Light source, 112...Wavelength selection mechanism, 113...Collimator lens, 114...Light projection lens, O...Object to be measured, L1...Incident light, L2...Scattered light, L3...Specularly reflected light.

Claims

1. A method for evaluating skin transparency, comprising irradiating the target skin with light and quantifying the amount of light that reaches a specific penetration depth by simulation, wherein the simulation is a reflected light intensity simulation using the skin's attenuation coefficient and skin's albedo.

2. The method according to claim 1, wherein the specific penetration depth is 2.0 mm or less from the surface of the skin.

3. The method according to claim 1, wherein the specific penetration depth is 0.1 mm or more and 0.8 mm or less from the surface of the skin.

4. The method according to any one of claims 1 to 3, wherein the transparency of the skin is the transparency of the skin as seen by the naked eye.

5. The method according to any one of claims 1 to 3, wherein the irradiating light includes a striped pattern having irradiated and non-irradiated areas on the skin.

6. The method according to claim 5, wherein the reflected light intensity used in the simulation is determined based on the lowest value in the luminance value distribution of the reflected light along the longitudinal direction of the irradiation unit.

7. A system comprising: a light irradiation means for irradiating an object to be measured with light containing light of a specific wavelength; a slit mask provided between the object to be measured and the light irradiation means, which forms a light-irradiated area and a light-non-irradiated area on the object to be measured; and a light-receiving means for receiving reflected light from the object to be measured.

8. The system according to claim 7, wherein the light irradiation means comprises a light source and a wavelength selection mechanism.

9. The system according to claim 7, wherein the light of the specific wavelength is visible wavelength light.

10. The system according to claim 7, wherein the light of the specific wavelength is light in the wavelength range of 360 nm to 830 nm.

11. The system according to claim 7, which is a system for use in a method for evaluating the transparency of skin.

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