JP7664601B2 - Pseudo stratum corneum for evaluating skin permeability and method for evaluating cosmetic permeability - Google Patents

Description

This invention relates to a pseudo stratum corneum for evaluating the permeability of cosmetics, which is used to evaluate the permeability of cosmetics from the skin surface to the stratum corneum, and a method for evaluating the permeability of cosmetics using the pseudo stratum corneum.

Human skin has an epidermis that protects the internal environment from the outside world, and its outermost layer is made up of the stratum corneum, which is approximately 0.02 mm thick.

The stratum corneum, also known as the stratum corneum, is made up of keratinocytes piled up like bricks, with intercellular substances embedded between them like mortar. The intercellular substances are made up of lipid molecular aggregates whose main components are ceramide, fatty acids, and cholesterol.

This stratum corneum prevents moisture from leaking out of the skin and maintains an appropriate amount of moisture, giving the skin flexibility and also protecting it from the invasion of foreign substances and irritation from outside the body.

Cosmetics that maintain the above-mentioned functions of the stratum corneum in good health include facial cleansers, lotions, beauty serums, emulsions, creams, and other cosmetics also known as basic cosmetics.

The functions of these cosmetic products are most effective when specific ingredients, which are formulated according to the purpose, are absorbed into the stratum corneum, so it is necessary to evaluate their permeability into the stratum corneum.

For example, a method is known in which a cosmetic is applied to a keratin film made from a solution of hair keratin protein using a finger, and the distortion and physical changes in shear force caused by the cosmetic being allowed to penetrate the film are measured over time, or the contact angle of a drop of the cosmetic applied to the skin is measured over time to indirectly examine the penetration of the cosmetic (Patent Document 1).

In addition, a method is known in which, using mammalian skin stratum corneum or cultured skin stratum corneum, the permeability of skin whitening agents, skin roughness prevention agents, etc. is examined by X-ray diffraction measurement of the stratum corneum, that is, by evaluating the area of the diffraction peak in a specific region in the X-ray diffraction profile, to examine whether or not the test substance has permeated into the stratum corneum (Patent Document 2).

Furthermore, a method for evaluating the permeability of cosmetics into the stratum corneum is known in which the stratum corneum is peeled off from the surface of the skin with adhesive tape using the tape stripping method, and observed under a microscope. The intensity of staining with fluorescein, rose bengal, or the like of the stratum corneum (specimen) taken before and after treating the skin to be observed with the cosmetic is compared by measuring the fluorescence brightness (Patent Document 3).

JP 2017-72397 A JP 2015-40702 A JP 2014-139540 A

However, the evaluation method described in Patent Document 1, which involves measuring the distortion and shear force of a keratin film and the change over time in the contact angle of a cosmetic droplet, cannot evaluate penetration in the depth direction.

In addition, the X-ray diffraction measurement using cultured skin stratum corneum, etc., described in Patent Document 2, estimates the permeability of a cosmetic from the stratum corneum after penetration, so although it can qualitatively determine whether or not a cosmetic has permeability, it is difficult to quantitatively compare differences in the degree of permeability, and X-ray diffraction measurement is not an evaluation method that can be easily performed.

In addition, the evaluation method described in Patent Document 3 allows the degree of rough skin to be determined by observing the surface of the stratum corneum sheet under a microscope, but it is difficult to grasp the difference in the grade of penetration ability of the same type of cosmetic into the stratum corneum, and it is not a method that allows cosmetic users to easily understand the difference in the penetration ability of the same type of cosmetic.

The object of this invention is to solve the problems in the prior art described above, to make it possible to clearly distinguish the permeability of cosmetics into the stratum corneum through simple and quantitative comparisons using a pseudo stratum corneum, and to make it possible to visually understand the relative merits of the permeability of various cosmetics into the stratum corneum, thereby enabling consumers to more accurately and easily distinguish between cosmetics with different permeability.

In order to solve the above problems, this invention uses a soft solid mixture containing keratin as the main component and 10 to 50 mass % lipids as an added component as a pseudo stratum corneum material, and a dye that is insoluble in the pseudo stratum corneum material but soluble in the cosmetic material to be evaluated is dispersed in the pseudo stratum corneum material to form a single-layer molded body to be used in a cosmetic material permeability evaluation test.

The pseudo stratum corneum of the present invention, constructed as described above, has a specific dye that is insoluble in the pseudo stratum corneum material and dissolves in the cosmetic material to be evaluated, and is dispersed in the pseudo stratum corneum material. When a cosmetic material is brought into contact with the surface of a single-layer molded product made of such a pseudo stratum corneum material, the dye that has penetrated the single-layer molded product from the surface dissolves in the cosmetic material and develops a color, thereby dyeing the pseudo stratum corneum material.

Therefore, by simply observing a single-layer molded body made of a pseudo-stratum corneum material from the thickness direction of the layer visually or by image, it is possible to directly and quantitatively grasp the extent to which a cosmetic agent has penetrated into the stratum corneum, as well as the penetration power of the cosmetic agent, taking into account factors such as the penetration depth over time.

It is preferable that the pseudo stratum corneum material is composed of components that have as similar a permeability as possible to the actual stratum corneum in order to accurately grasp the permeability of the cosmetic, so the lipids are preferably one or more lipids selected from squalene, ceramide, fatty acid, and cholesterol.

For the same reason as above and to correspond to the softness of the stratum corneum on the actual skin surface, the lipid preferably contains 10% by mass or more of a lipid component that is liquid at room temperature, more preferably the lipid component that is liquid at room temperature is a lipid component containing squalene or oleic acid or both, and further preferably the blending ratio of the keratin to the lipid is 6:4 to 8:2 by mass.

Furthermore, the dye can be any dye that dissolves in the cosmetic to be evaluated depending on its polarity. In other words, if the dye dispersed in the pseudo stratum corneum dissolves and develops color depending on the polarity of the cosmetic to the depth to which the cosmetic has penetrated, the penetration power of the cosmetic into the stratum corneum (depth of penetration) can be visually grasped from the colored dye by simply observing the pseudo stratum corneum visually or with an image.
The dye that exhibits such an effect may be either a water-soluble dye or an oil-soluble dye, and may be, for example, a water-soluble dye that is soluble in a cosmetic composition containing 15 to 95% by mass of water.

In particular, when the dye is a water-soluble acid dye, it dissolves in water and is ionically bonded to the amino groups of keratin to dye the skin. As a result, the dye remains at the colored position, making it possible to accurately grasp differences in the penetration speed of the cosmetic into the stratum corneum and differences in the depth at which it can penetrate. Favorable results can be obtained by using azulene sulfonate or water-soluble food coloring as such a water-soluble acid dye.

In this way, the above-described pseudo stratum corneum can be used to contact the surface with a cosmetic, and the depth to which the cosmetic has penetrated from the surface can be visually determined by the color reaction of the dye that progresses over time, thereby evaluating the penetration of the cosmetic.

As described above, this invention uses a soft solid mixture containing keratin as the main component and a specified amount of lipids as an added component as a pseudo stratum corneum material, and a single-layer molded body in which a dye that is insoluble in this pseudo stratum corneum material and soluble in the cosmetic material to be evaluated is dispersed and held in a pseudo stratum corneum. This is used to perform a cosmetic material permeability evaluation test, so that the cosmetic material is brought into contact with the surface of the pseudo stratum corneum, and the depth of penetration of the cosmetic material from the surface can be visually determined by the color reaction of the dye that progresses over time, thereby evaluating the cosmetic material's permeability.

This allows for easy and clear discrimination of the permeability of cosmetics into the stratum corneum using a pseudo stratum corneum, and also allows users to visually understand the relative merits of the permeability of various cosmetics into the stratum corneum, which has the advantage that consumers can more accurately distinguish between cosmetics with different permeability.

Photographs showing the results of visual evaluation tests of the examples FIG. 1 is a diagram showing the relationship between test time (min) and penetration depth (mm) showing the results of visual evaluation tests in the examples.

The pseudo stratum corneum of this embodiment of the invention is a single-layer molded body that uses a pseudo stratum corneum material made of a soft solid mixture containing keratin as the main component and 10 to 50 mass % lipids as an added component, and that contains in a dispersed state a dye that is insoluble in the pseudo stratum corneum material and dissolves in the cosmetic product to be evaluated.

The keratin used in the above embodiment can be a commercially available product called keratose or keratose powder, which is prepared by sufficiently oxidizing a low molecular weight powdery substance obtained by hydrolysis of a raw material of biological origin such as wool. Keratose powder is a material that exhibits moisturizing properties, water absorption, water permeability, and oil absorption, and is also commercially available as an ingredient in cosmetics and a moisture absorption and release regulator.

The lipids used in this invention are selectively adopted to mimic intercellular lipids in the stratum corneum, and it is preferable to adopt one or more lipids selected from, for example, squalene, ceramide, fatty acid, and cholesterol.

Squalene is a component that accounts for approximately 13% of human sebum, and commercially available squalene includes that extracted from shark liver oil.

Ceramide is a component of cell membranes and an intercellular lipid in the human stratum corneum. It is a compound formed by an amide bond between sphingosine and a fatty acid. Well-known human ceramides produced using yeast, etc., natural ceramides, ceramides extracted from plants such as rice bran oil, and synthetic ceramides can be used.

The fatty acid is preferably one with a molecular weight similar to that of free fatty acids released into the blood when body fat is decomposed by lipase, and examples of the fatty acids that can be used include long-chain fatty acids present in adipose tissue, such as behenic acid, palmitic acid, and stearic acid.

Cholesterol is purified from natural products and is a solid, white or pale yellow powder at room temperature; it is an industrial material that is also used in cosmetics, pharmaceuticals, liquid crystals, etc.

In order to form a single-layer molded article into which the cosmetic preparation can easily penetrate, it is preferable that such lipids are compositions containing 25 mass% or more of lipid components that are liquid at room temperature, such as squalene and oleic acid, as well as solid lipids with melting points higher than room temperature, such as ceramide, cholesterol, and behenic acid (free fatty acid).

In addition, the amount of lipid to keratin (mass ratio) is preferably 6:4 to 8:2 in order to make the pseudo stratum corneum homogeneous and to ensure sufficient permeability of the cosmetic. If the ratio of lipid to keratin is small and less than the above-mentioned specified range, voids are likely to occur in the pseudo stratum corneum before the cosmetic penetrates, which is undesirable as the density within the layer becomes non-uniform, and the permeability becomes too high, which is undesirable as it loses the same level of hydrophobicity as skin. For these reasons, a more preferable amount of lipid to keratin (mass ratio) is 6:4 to 7:3.

The dye used in this invention is selectively one that is insoluble in the constituent components of the pseudo stratum corneum material described above and soluble in the cosmetic material to be evaluated; if the cosmetic material is an aqueous cosmetic material, a water-soluble dye that can dissolve in it is used; and if the cosmetic material is an oil-based cosmetic material, an oil-soluble dye that can dissolve in it is used.
The water-based cosmetic preparations used in this invention for permeability evaluation are those whose continuous phase is composed mainly of water or a water-soluble component, including O/W type emulsion cosmetic preparations.Similarly, the oil-based cosmetic preparations used in this invention for permeability evaluation are those whose continuous phase is composed mainly of oil or an oil-soluble component, including W/O type emulsion cosmetic preparations.

Among the water-soluble dyes mentioned above, it is preferable to use water-soluble acid dyes. When such water-soluble acid dyes dissolve in the water in the cosmetic, the acid dyes ionically bond to the amino groups of the keratin that constitutes the pseudo stratum corneum, and are dyed. As the dye thus colored remains in place, the penetration position of the cosmetic in the pseudo stratum corneum is fixed over time, so that even if the pseudo stratum corneum is not left stationary but moves or tilts, the dye remains in the specified position, and the penetration of the cosmetic into the stratum corneum can be more reliably understood. For the same reason, when using oil-soluble dyes, it is preferable to use oil-soluble acid dyes.

Specific examples of the water-soluble acid dye include azulene sulfonate and water-soluble food dyes.
The water-soluble dye is a dye that has a hydrophilic group, such as sodium sulfonate, and is easily soluble in water. For example, sodium azulene sulfonate, New Coccine (commonly known as Food Red No. 102), etc. can be used.

As oil-soluble dyes, there are the above water-soluble dyes that have been made insoluble in water by treating them with calcium sulfate, barium salts, etc. Water-soluble dyes can also be made insoluble in water by treating them with calcium sulfate, zirconium sulfate, etc.

It is preferable to add sodium chloride in addition to the above-mentioned constituent ingredients of the pseudo stratum corneum, because this allows for a more accurate evaluation of the permeability of the cosmetic agent into skin that physiologically contains sodium chloride.

Furthermore, adding sodium chloride to the constituent materials of the pseudo stratum corneum makes it possible to evaluate the properties of cosmetics that react to salt on the skin. The preferred ratio of sodium chloride, in mass ratio, keratin:lipid:sodium chloride is 6.0-6.75:3.25-4.0:0-0.5, in order to reproduce the skin in an actual sweating state.

To prepare the constituent raw materials of the pseudo stratum corneum described above, the blending ratio (mass ratio) of lipid to keratin is 6:4 to 8:2. In other words, the constituent raw materials (100 mass%), which are composed mainly of keratin, with 20 to 40 mass% lipid as an added component, a specified dye and other added components (surfactants, etc.) blended as necessary, are mixed into a paste-like form, and it is preferable to knead them so that the specified dye is uniformly dispersed.

The obtained paste-like mixture is placed in a transparent cylindrical container such as a test tube or cell, and a pseudo-stratum corneum is formed as a single-layer molded body of appropriate thickness so that the difference in the permeability of various cosmetic materials can be visually confirmed.
For example, it is preferable that the material is filled into the closed end of the container so as to form a uniform single-layer molded product of about 1 to 1,000 mm, and the surface of the pseudo stratum corneum facing the opening of the container is molded into a substantially flat surface similar to the surface of skin.

In this invention, the type of cosmetic is not particularly limited, but it is preferable that the cosmetic contains 15 to 95% water by mass. For example, lotions and gels that contain 30 to 95% water by mass per 100% by mass, and liquid, cream, and semi-solid cosmetics made from emulsion compositions that contain approximately 15 to 95% water by mass are preferable as the subject of the test. In addition, even if the cosmetic is made from a powder or compressed powder, cosmetics to which an appropriate amount of water has been added can be used as the subject of the test, assuming a state in which the cosmetic contains 15% or more water by mass on the skin.

These test cosmetic products can contain ingredients that are typically found in lotions and other basic cosmetics, without any particular restrictions. For example, they may contain glycerin, NMF components, hyaluronic acid, etc.

The cosmetic material of the above embodiment is poured or layered into the cylindrical container so as to cover the entire surface of the pseudo stratum corneum, and if necessary, is applied with a pressure similar to that applied to the skin when in use.

The time that has elapsed since the contact is then recorded, and the depth to which the cosmetic has penetrated from the surface is evaluated by the color reaction of the dye, and if necessary, the penetration of the cosmetic can be evaluated by recording it in photographs (still images) or video (moving images).

Keratin as a protein, squalene as a lipid, and sodium chloride as a salt were mixed in a mass ratio of 10:5.2:0.8, and 0.4 mass% of sodium azulene sulfonate, a water-soluble acid dye capable of dyeing keratin protein blue, was added to 100 mass% of this mixture. The mixture was mixed using a three-roller mill until it became a paste-like material so that the plastic components were uniformly dispersed, preparing a grayish-white pseudo-stratum corneum material.

The pseudo stratum corneum material obtained as described above was filled into multiple spectrophotometer cells, which are transparent containers of uniform volume, without leaving any voids inside, to form a single-layer molded body. This was used as a pseudo stratum corneum for cosmetic permeability evaluation tests, and the number of samples required for the following tests (9 pieces) was prepared.

Using the obtained simulated stratum corneum of the Example, a permeability evaluation test for cosmetics A, B and a control (purified water) was carried out as follows.
Cosmetics A and B are lotions (skin lotions) of different commercial grades, and contain mainly moisturizing ingredients and purified water, but differ slightly in the amount of polyols blended.

As samples, cosmetic A, cosmetic B, and control (purified water) were dropped in equal amounts (0.4 ml) into the cell filled with the simulated stratum corneum of the example so that the simulated stratum corneum was fully immersed, and the cell was left to stand.

The depth (mm) from the surface of the pseudo stratum corneum where the sample had come into contact with the sample and had turned blue over time from the surface to the deeper parts was visually evaluated from the front of each pseudo stratum corneum 5 minutes, 30 minutes, 45 minutes, 60 minutes, and 120 minutes after the dropping. Digital images taken from the same positions were analyzed to accurately determine the penetration depth, and the results are shown in Table 1 and Figures 1 and 2.

In Figure 1, a dotted line is drawn at the boundary between the dye or water permeation area and the non-permeation area to clearly show the penetration depth of the cosmetic material into the simulated stratum corneum in the figure (photograph). For each sample, the above test was performed three times for each measurement and evaluation, and the average penetration depth is plotted in Figure 2, with a line connecting the maximum and minimum values also drawn on the figure.

As is clear from the results in Table 1 and Figures 1 and 2, Cosmetic Preparations A and B were found to have higher permeability into the simulated stratum corneum of the Examples than purified water as a control, and the difference in permeability of Cosmetic Preparation A compared to Cosmetic Preparation B could be easily and clearly visually determined simply by visual inspection of the photograph in Figure 1. This could also be determined more accurately from the results of image analysis shown in Figure 2 and Table 1.
From these results, it was confirmed that consumers can more accurately and easily distinguish between cosmetics A and B, which have different permeability, by using the pseudo stratum corneum of the examples.

Claims (9)

The pseudo stratum corneum for cosmetic permeability evaluation tests is a single-layer molded body in which a soft solid mixture containing keratin as the main component and 10 to 50 mass % of one or more lipids selected from squalene, ceramide, fatty acid and cholesterol as an added component is used as a pseudo stratum corneum material, and a dye that is insoluble in the pseudo stratum corneum material but soluble in the cosmetic material to be evaluated is dispersed in the pseudo stratum corneum material. The pseudo stratum corneum for use in a cosmetic permeability evaluation test according to claim 1 , wherein the lipid contains 10% by mass or more of a lipid component that is liquid at room temperature. 3. The pseudo stratum corneum for use in a cosmetic permeability evaluation test according to claim 2 , wherein the lipid component which is liquid at room temperature is a lipid component containing squalene , oleic acid, or a combination of both. The pseudo stratum corneum for use in a cosmetic permeability evaluation test according to any one of claims 1 to 3 , wherein a blending ratio by mass of said keratin and said lipid is from 6:4 to 8:2. The pseudo stratum corneum for use in a cosmetic permeability evaluation test according to any one of claims 1 to 4 , wherein the dye is a water-soluble dye that is soluble in a cosmetic containing 15 to 95% by mass of water. The pseudo stratum corneum for use in a cosmetic permeability evaluation test according to claim 5 , wherein the water-soluble dye is a water-soluble acid dye. The pseudo stratum corneum for use in a cosmetic permeability evaluation test according to claim 6 , wherein the water-soluble acid dye is an azulene sulfonate or a water-soluble food dye. A method for evaluating the permeability of a cosmetic, comprising contacting a cosmetic with the surface of the pseudo stratum corneum according to any one of claims 1 to 7 and evaluating the depth of penetration of the cosmetic from the surface by a color reaction of a dye. 9. The method for evaluating the permeability of a cosmetic according to claim 8 , wherein the cosmetic contains 15 to 95% by mass of water.

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