Composition for skin external application

Abstract

The purpose of the present invention is to develop a novel product that produces a pore-improving effect through a mechanism of action which has been specified by studying conventional pore-improving solutions focusing on the mechanisms of action of the conventional pore-improving solutions.　As a result of studies on the pore-improving effect, which is known as a peeling effect, of glycolic acid, it has been found that glycolic acid can exhibit a sebum production-inhibiting effect even at near-neutral pH. The present invention provides a composition for skin external application, the composition containing an α-hydroxy acid having 6 or less carbon atoms or a salt thereof and having a pH of more than 5.0 but not more than 8.0.

Description

Topical composition for skin 【0001】 The present invention relates to a composition for application to the skin. More specifically, the present invention relates to a topical composition for improving the appearance of pores and / or comedones on the skin. 【0002】 Although the number of pores on the skin is innate and does not change, clogged comedones, darkening, and opening of the pores make the pores prominent and greatly affect the aesthetic appearance. It is required to suppress the visibility of pores through skin care, and as pore improvement solutions, cosmetics such as peeling packs, AHA / BHA pads, oil cleansing, enzyme cleansing, and beauty treatments such as hydrafacials are provided. However, there are almost no products that show a systematic mechanism of action, and research aiming for a high pore improvement effect by a multi-faceted combination of solutions has been slow to progress. As agents that exhibit a peeling action on the cutin, acids such as glycolic acid, salicylic acid, and lactic acid are known (Patent Document 1: JP-A-2008-231010, Patent Document 2: Patent No. 3391955, Patent Document 3: JP-A-7-277918, Patent Document 4: JP-A-2016-29076), and peeling agents containing any one or a combination of these are commercially available. Furthermore, it has been reported that applying a low pH cream containing glycolic acid and salicylic acid reduces the amount of sebum produced (Non-Patent Document 1: J. Appl. Cosmetol. 15, 21-32 (1997)). In addition, C6-C20 carboxylic acids have been shown to exhibit a sebum-suppressing effect (Patent Document 5: JP-A-8-48625). 【0003】 JP-A-2008-231010, Patent No. 3391955, JP-A-7-277918, JP-A-2016-29076, JP-A-8-48625 【0004】 J. Appl. Cosmetol. 15, 21-32 (1997) 【0005】 Regarding the pore improvement solutions provided so far, research is conducted focusing on the mechanism of action, aiming at the development of new products that produce a pore improvement effect through the identified mechanism of action. 【0006】 Glycolic acid, known for its peeling effect, provides a high pore-improving effect, but its low pH makes it highly irritating. The present inventors investigated the pore-improving effect of glycolic acid and found that glycolic acid can exert a sebum production inhibitory effect even at a pH near neutral, leading to the present invention. Therefore, the present invention relates to the following: [1] A topical skin composition comprising an α-hydroxy acid having 6 or less carbon atoms or a salt thereof, with a pH greater than 5.0 and 8.0 or less. [2] The topical skin composition according to item 1, comprising 0.5% to 5% by mass of an α-hydroxy acid or a salt thereof. [3] The topical skin composition according to item 1 or 2, wherein the α-hydroxy acid is at least one selected from the group consisting of glycolic acid, glyceric acid, tartaric acid, 2-hydroxybutyric acid, malic acid, tartaric acid, citric acid, and gluconic acid. [4] The topical skin composition according to any one of items 1 to 3, used for inhibiting sebum production. [5] A topical skin composition according to any one of items 1 to 4, for use in improving the appearance of enlarged pores and / or blackheads. [6] A topical skin composition according to item 5, for reducing the appearance of enlarged pores by inhibiting sebum production. [7] Use of a topical skin composition according to any one of items 1 to 6 for the manufacture of a cosmetic or pharmaceutical for inhibiting sebum production. [8] Use of a topical skin composition according to any one of items 1 to 6 for the manufacture of a cosmetic or pharmaceutical for reducing the appearance of enlarged pores by inhibiting sebum production. [9] Use of a topical skin composition according to any one of items 1 to 6 for the manufacture of a cosmetic or pharmaceutical for improving the appearance of enlarged pores and / or blackheads.

[10] A cosmetic method for inhibiting sebum production, comprising applying a topical skin composition according to any one of items 1 to 6 to skin of a person concerned about sebum production.

[11] A cosmetic method for reducing the appearance of enlarged pores, comprising applying a topical skin composition according to any one of items 1 to 6 to skin of a person concerned about enlarged pores.

[12] A cosmetic method for improving the appearance of blackheads, comprising applying a topical skin composition described in any one of items 1 to 6 to the skin of a person concerned with visible pores and / or visible blackheads. 【0007】By incorporating an α-hydroxy acid or its salt with six or fewer carbon atoms to achieve a pH greater than 5.0 and 8.0 or less, an effect of improving the appearance of enlarged pores and / or blackheads is exerted. This effect is achieved through the suppression of sebum production. 【0008】 Figure 1 shows the amount of sebum produced when (A) a test composition containing glycolic acid at pH 4.0 and (B) a test composition containing glycolic acid at pH 7.0 were applied. Figure 2 shows the subjective evaluation results immediately after 4 weeks of continuous use of the test composition containing glycolic acid at pH 7.0 (A). Figure 2 shows the subjective evaluation results 4 weeks after discontinuing continuous use of the test composition containing glycolic acid at pH 7.0 (B). Figure 2 shows the subjective evaluations after applying the test composition containing glycolic acid at pH 7.0 and the test composition containing glycolic acid at pH 4.0 (C). Figure 2 shows the results of the physician's evaluation immediately after 4 weeks of continuous use of the test composition containing glycolic acid at pH 7.0 (D). Figure 3 shows the change in pore area on the nose immediately after 4 weeks of continuous use of the test composition containing glycolic acid at pH 7.0 and after 4 weeks of discontinuation. Figure 4 shows the change in oil droplet production when cultured cells were cultured in test solutions (pH 7.1) with varying concentrations of glycolic acid. Figure 5 shows the results of investigating the effect of pH on the oil droplet production of glycolic acid in cultured cells. Figure 6 shows the amount of oil droplets produced using a test solution containing lactic acid at a neutral pH. Figure 7 shows magnified photographs of pores on the nose after 4 weeks of continuous use of a test composition containing glycolic acid at pH 7.0, and after a further 4-week discontinuation period. Figure 8A shows the results of measuring sebum secretion on the cheeks after 4 weeks and 8 weeks of continuous use of test solutions containing glycolic acid, niacinamide, and glycylglycine at pH 6.5 to 7.5 for 8 weeks. Figure 8B shows the change in total pore area measured by the replica method after the same continuous use test. 【0009】 The present invention relates to a topical skin composition comprising an α-hydroxy acid having 6 or fewer carbon atoms or a salt thereof, having a pH greater than 5.0 and a pH of 8.0 or less. By incorporating an α-hydroxy acid or a salt thereof, it is possible to exert sebum production inhibitory effects and pore improvement effects, and by having a pH greater than 5.0 and a pH of 8.0 or less, irritation can be reduced. 【0010】 While the number of pores does not change with age, pores become more noticeable as we age. Pores enlarge due to increased sebum production, which causes them to become clogged with keratin plugs, and they also become more noticeable when dirt and other blackheads accumulate deep within the pores. In addition, the unsaturated fatty acids contained in the sebum produced act on the keratinocytes around the pores, causing incomplete keratinization, which makes the pores appear funnel-shaped and more noticeable. In other words, there are at least two causes of noticeable pores: one is when pores become more noticeable due to increased sebum production and subsequent clogging with keratin plugs, and the other is when the unsaturated fatty acids in the sebum cause the pores to become funnel-shaped, resulting in them appearing shadowed and more noticeable. 【0011】 Conventional peeling compositions containing alpha-hydroxy acids were known to exhibit a peeling effect on skin exhibiting keratinization, such as rough skin and acne. This peeling effect is thought to be due to the low pH acting on the keratin, causing exfoliation. It is believed that the low pH acts on corneodesmosomes, which contribute to intercellular adhesion in the stratum corneum, breaking them down and thereby promoting desquamation. By promoting desquamation, normal skin turnover can be promoted, and this gradually restores the funnel-shaped pores, resulting in a pore-improving effect. On the other hand, a low pH is required to exert the peeling effect, and it can cause irritation when applied to the skin. Therefore, it is recommended that people with sensitive skin or those with delicate skin avoid using peeling agents. 【0012】In this invention, we focused on the fact that α-hydroxy acids or their salts exert not only peeling effects but also other physiological effects, and found that they exert a sebum production inhibitory effect (Figure 1). The sebum production inhibitory effect of α-hydroxy acids or their salts is exerted even at the low pH range where they are conventionally used as peeling agents. However, we found that when formulated at a neutral pH of 5.0 to 8.0, particularly in any pH range selected from pH 5.0 to 5.5, pH 5.5 to 6.0, pH 6.0 to 6.5, pH 6.5 to 7.0, pH 7.0 to 7.5, and pH 7.5 to 8.0, or in a continuous pH range, they exert a sebum production inhibitory effect similar to that when formulated at a low pH (Figure 1). By suppressing sebum production, the formation of comedones can be suppressed, and thereby the enlargement of pores can also be suppressed. This point was also investigated in a half-face test, and the questionnaire results showed that continuous use of the topical skin composition according to the present invention improved pores, blackheads, skin smoothness (roughness, smoothness), and skin condition (softness, brightness, lotion absorption, makeup application) after continuous use (Figure 2A). Furthermore, it was shown that the improvement effect persisted to some extent even after continuous use for four weeks and then a four-week break (Figure 2B). Compared to the application of a low-pH glycolic acid serum, the improvement effect on pores, blackheads, skin smoothness (roughness, smoothness), and skin condition (softness, brightness, lotion absorption, makeup application) after applying a neutral-pH glycolic acid serum was equivalent to or better than that of the low-pH glycolic acid serum (Figure 2C). In addition, physician evaluations also showed improvement in pores and blackheads on the nose (Figure 2D). Although low-pH glycolic acid serums differ from neutral glycolic acid serums in terms of frequency of use due to their irritancy, the usefulness of neutral-pH glycolic acid in improving pores is demonstrated. Furthermore, in a comparison of pore area by taking photographs of pores on the skin after applying the topical skin composition of the present invention, it was shown that the pore area decreased after continuous use of the topical skin composition of the present invention, and that this effect was maintained even after the end of continuous use (Figures 3 and 7). In addition, in a half-way test, a test solution containing glycolic acid, niacinamide, and glycylglycine was used continuously for 8 weeks, and the amount of sebum and total pore area of ​​the cheeks were measured after 4 weeks and 8 weeks.On the cheek where the test solution was applied, a significant decrease in sebum volume was observed at 4 weeks and 8 weeks compared to before application. At 8 weeks, a greater decrease in sebum volume was observed in the test solution application group compared to the placebo group (Figure 8A). In addition, a significant decrease in total pore area was observed in the test solution application group compared to the placebo group at 4 weeks (Figure 8B). These in vivo tests demonstrate that the topical skin composition of the present invention has a sebum production inhibitory effect and exhibits a pore improvement effect. 【0013】 Furthermore, the sebum production inhibitory effect has been investigated in vitro using sebaceous gland cells. Glycolic acid can reduce sebum production in a dose-dependent manner at pH 7.1 (Figure 4). It was shown that adding a test solution containing glycolic acid at a pH greater than 5.0 (neutral) and 7.5 or less to a culture medium reduced the amount of oil droplets produced by sebaceous gland cells (Figure 5). It was also shown that this sebum production inhibitory effect tends to occur with lactic acid, which is an α-hydroxy acid other than glycolic acid (Figure 6). Salicylic acid is a compound that has been conventionally used as a peeling agent and is an agent that exhibits a pore-improving effect, so the sebum production inhibitory effect of the α-hydroxy acid used in this invention can be said to be an effect that can be clearly distinguished from stratum corneum exfoliation due to low pH. 【0014】While not intended to be limited to theory, the α-hydroxy acid or its salt incorporated into the topical skin composition of the present invention does not exert a pore-improving effect based on its stratum corneum exfoliating effect due to its low pH, but rather exerts a pore-improving effect through the suppression of sebum production. Therefore, the topical skin composition of the present invention can be used to improve the appearance of enlarged pores and / or prominent blackheads, and is particularly useful for improving the appearance of enlarged pores and / or prominent blackheads through the suppression of sebum production. The topical skin composition of the present invention can also be described as a non-peeling method for improving the appearance of enlarged pores and / or prominent blackheads. Being non-peeling reduces irritation due to its low pH, making it applicable to sensitive skin, skin with minor wounds, and skin with impaired skin barrier function. The composition of the present invention can be applied to individuals concerned about sebum production, individuals concerned about enlarged pores, or the skin of individuals concerned about sebum production. The present invention may also relate to a sebum production inhibitor comprising an α-hydroxy acid or its salt, with a pH of 5.0 to 8.0. Peeling agents are not typically used repeatedly due to their irritating nature. On the other hand, the topical skin composition of the present invention is low-irritant, exerts an inhibitory effect on sebum production, and can be used daily at least once a day, for example, twice a day, in the morning and evening. The duration of continuous use is not particularly limited, but it can be used for a long period of time, such as one week or more, two weeks or more, one month or more, two months or more, three months or more, six months or more, or one year or more. 【0015】 Alpha-hydroxy acids with 6 or fewer carbon atoms are given by the following formula: In the formula, R is hydrogen, a C1-C4 alkyl, or a substituted C1-C4 alkyl. A substituted C1-C4 alkyl refers to a C1-C4 alkyl substituted with -OH or a C1-C3 alkyl substituted with -COOH. Therefore, the number of carbon atoms is 6 or less, while the number of atoms is 2 or more. The alkyl may be linear or branched, or cyclic. Examples of such α-hydroxy acids include glycolic acid (2 carbon atoms), glyceric acid (3 carbon atoms), tartaric acid (3 carbon atoms), 2-hydroxybutyric acid (4 carbon atoms), malic acid (4 carbon atoms), tartaric acid (4 carbon atoms), citric acid (6 carbon atoms), and gluconic acid (6 carbon atoms). These α-hydroxy acids may be used alone or in combination. 【0016】 The α-hydroxy acid salt may be any salt that can be used in cosmetics, and examples include sodium salts, potassium salts, calcium salts, magnesium salts, and ammonium salts. The α-hydroxy acid is an acid to weak acid compound and may be in a free state depending on the pH of the solution, or it may form a salt with the base of other components that are included in the formulation. 【0017】 Alpha-hydroxy acids or their salts can be incorporated at a concentration of 0.5% to 5% by mass. From the viewpoint of exhibiting a pore-improving effect, 0.65% or more by mass, or 1.0% or more by mass, is preferred. From the viewpoint of suppressing skin irritation, 4.0% or less by mass, or 3.0% or less by mass, is particularly preferred. 【0018】The pH of the topical skin composition of the present invention is greater than 5.0 and 8.0 or less. From the viewpoint of reducing irritation, a pH of 5.1 or higher, 5.5 or higher, or 6.0 or higher is preferred. From the viewpoint of exhibiting a pore-improving effect, a pH of 7.5 or lower, 7.0 or lower, or 6.5 or lower is preferred. Any range can be formed from these upper and lower limits. That is, one or more consecutive ranges can be selected from pH 5.1-5.5, 5.5-6.0, 6.0-6.5, 6.5-7.0, 7.0-7.5, and 7.5-8.0. From the viewpoint of maintaining the pH within the predetermined range, it is preferable to include a neutralizing agent and / or buffering agent. Any buffering agent that is commonly used in cosmetics, pharmaceuticals, and quasi-drugs can be used. As a neutralizing agent, any basic substance that can be incorporated into cosmetics is acceptable, and examples include sodium hydroxide, potassium hydroxide, and ammonium. Any buffering agent that can be incorporated into cosmetics is acceptable, and examples include citrate buffer, phosphate buffer, TRIS, HEPES, MES, MOPS, etc. The buffering agent should be incorporated at a concentration that can achieve the desired pH, and as an example, it can be incorporated at a concentration of 0.01 mM to 100 mM, preferably 0.1 mM to 50 mM, and more preferably 1 mM to 20 mM. 【0019】 A topical skin composition refers to a composition that can be applied directly to the skin, and more particularly to a composition for improving the appearance of enlarged pores and / or blackheads. A topical skin composition is not particularly limited as long as it can be applied to the skin, and any dosage form can be applied, such as solution, emulsion, solid, semi-solid, powder, powder dispersion, water-oil two-layer separation, water-oil-powder three-layer separation, ointment, gel, stick, pack, etc. A topical skin composition may contain bases, thickeners, excipients, neutralizing agents, preservatives, emulsifiers, cosmetic ingredients, etc., that are commonly used in topical skin compositions. 【0020】In the present invention, a thickening agent may or may not be included. As the thickening agent, water-soluble polymers such as xanthan gum, gellan gum, guar gum, hydroxypropyl methylcellulose, hydroxyethylcellulose, propylene glycol alginate, and polyacrylamide, which are components usable in cosmetics, pharmaceuticals, or other pharmaceuticals, can be used. The thickening agent may be included in an amount of 0.1 to 10% by mass, for example, 0.5 to 7.0% by mass. In conventional cases where α-hydroxy acids are used as peeling agents, a thickening agent is added to prevent them from dripping into the eyes or nose due to their low pH and irritating properties. However, in the present invention, since the formulation is at a neutral pH and has low irritancy, a thickening agent may not be included, or it may be included to achieve low viscosity. For example, to achieve low viscosity, it may be included in an amount of less than 0.1% by mass. 【0021】 Other cosmetic ingredients that may be used include those with exfoliating and moisturizing properties. Retinoids, which exert desquamating and keratinocyte differentiation stimulating effects, may or may not be included. 【0022】 Such compositions may be cosmetics, pharmaceuticals, or quasi-drugs. When the composition is used as a cosmetic, it can be incorporated into facial or body cosmetics such as lotions, emulsions, serums, creams, packs, essences, and gels, as well as makeup cosmetics such as foundations, makeup bases, and concealers, and even bath additives. When incorporated into pharmaceuticals or quasi-drugs, it can be used as a topical skin preparation. Due to the difficulty in forming the dosage form, dosage forms using sprays such as topical aerosol foams are not included in the compositions of the present invention. Topical skin compositions can be administered over a long period of time. From the viewpoint of exhibiting an effect of improving the appearance of enlarged pores and / or blackheads, it may be administered for several days or more, one week or more, two weeks or more, one month or more, three months or more, or six months or more. There is no particular upper limit, but it may be several years or less, for example, one year or less. 【0023】Another aspect of the present invention may relate to a beauty method comprising applying a topical skin composition comprising an α-hydroxy acid having 6 or fewer carbon atoms or a salt thereof, and having a pH of 5.0 to 8.0. The beauty method of the present invention may be offered as a service in beauty salons, beauty clinics, etc., or may be offered together with the sale of cosmetics in cosmetic retail stores. The beauty method is a non-therapeutic or non-medical method that can be distinguished from treatment or preventive methods performed by doctors or medical professionals, and is provided by practitioners who are not doctors or other medical professionals. 【0024】 All references made herein are incorporated herein by citation in their entirety. 【0025】 The embodiments of the present invention described below are for illustrative purposes only and do not limit the technical scope of the invention. The technical scope of the invention is limited solely by the claims. Modifications to the invention, such as additions, deletions, and substitutions of constituent elements of the invention, can be made without departing from the spirit of the invention. 【0026】 Example 1: Half-Face Test A half-face test was conducted on 32 women in their 20s, 30s, and 50s who were concerned about blackheads and pores. The face was divided into the right and left halves, and the test solution was applied to only one half. The subjects were divided into a low pH test group and a neutral pH test group. The test solution was applied to the low pH test group and the neutral pH test group for 2 weeks or 4 weeks, respectively, according to the protocol below, and the following measurement set was performed: (A) measurement of sebum amount, (B) acquisition of pore images, and (C) questionnaire. (A) Sebum amount was measured on the cheeks and nose using a Sebumeter (Courage + Khazaka electronic GmbH). (B) Pore images were acquired using a Microscope (Integral Co., Ltd.) to obtain images of pores on the nose, and the pore area was measured by 2D evaluation (please specify the software). Images of pores on the nose are shown in Figure 7. (C) For the four items of pores (cheeks), pores (nose), blackheads (nose), and skin smoothness, subjective evaluations were conducted using a questionnaire, divided into five levels: very poor, poor, average, good, and very good. 【0027】As the low pH test solution for the test group, a low pH test solution containing 4% by mass glycolic acid, adjusted to pH 4.0 with caustic soda and sodium citrate, was used. On the first day of the test, after washing the face and allowing it to acclimate to the environment for one hour, measurement sets were made on both the right and left halves of the face (Day 0). From days 1 to 14, the low pH test solution was applied to the left half of the face after washing the face at night once every three days and rinsed off after 5 minutes (four applications between days 1 and 14). On day 15, after washing the face and allowing it to acclimate to the environment for one hour, measurement sets were made on both the right and left halves of the face. From days 15 to 42, the subjects used their usual cosmetics (four weeks of drug-free period). On day 42, after washing the face and allowing it to acclimate to the environment for one hour, measurement sets were made on both the right and left halves of the face. Because the low pH test solution is irritating, for safety reasons, it should be used once every three days, and this should be done four times over a two-week period. 【0028】 As the neutral pH test solution, a neutral pH test solution containing 4% by mass glycolic acid and adjusted to pH 7.0 with caustic soda and sodium citrate was used. On the first day of the test, after washing the face and allowing it to acclimate to the environment for one hour, measurement sets were made on both the right and left halves of the face (Day 0). From days 1 to 28, the neutral pH test solution was applied to the left half of the face every morning and evening after washing the face (continuous use for 4 weeks). On day 29, after washing the face and allowing it to acclimate to the environment for one hour, measurement sets were made on both the right and left halves of the face. From days 29 to 56, the subjects used their usual cosmetics (4 weeks of drug-free period). On day 56, after washing the face and allowing it to acclimate to the environment for one hour, measurement sets were made on both the right and left halves of the face. Since the neutral pH test solution is not irritating, it was used twice a day, morning and evening, for 4 weeks. 【0029】 Figure 1 shows the results of measuring nasal sebum levels in (A) the low pH test group and (B) the neutral pH test group. In the (A) low pH test group, there was no change in nasal sebum levels immediately after 2 weeks of continuous use, but it decreased significantly after discontinuation of the drug. On the other hand, in the (B) neutral pH test group, sebum levels decreased significantly after 4 weeks of continuous use, and this significant decrease in sebum levels continued even after 4 weeks of discontinuation of the drug. 【0030】Figure 2 shows the results of the neutral pH test group, including (A) questionnaire results after 4 weeks of continuous use, (B) questionnaire results after 4 weeks of discontinuation, (C) questionnaire results for the neutral pH test solution and the low pH test solution, and (D) physician evaluation results. After continuous use of the neutral pH test solution, subjective evaluations of nasal pores, blackheads, and skin smoothness were high, and physician evaluations of nasal pores and blackheads were also high. 【0031】 Figure 3 shows the change in pore area in the neutral pH test group. Compared to before application, continuous use of the neutral pH test solution for 4 weeks resulted in a decrease in nasal pore area. 【0032】 Example 2: In vitro sebum production measurement test Human sebaceous gland cells collected from a 50-year-old woman were cultured in sebaceous gland culture medium (TI Corporation). During subculturing, 2 × 10 ４ Cells were seeded in 24 plates at 37°C and 5% CO2. ２ Cells were cultured under atmospheric conditions for 6 days. A differentiation induction reagent (CTI) was added to a concentration of 0.1% by mass to induce differentiation. The culture was then replaced with a test solution containing 100 mM glycolic acid, adjusted to pH levels of 2.4, 3.6, 4.0, 5.0, and 7.5, and incubated for 2 minutes. Control groups were used: a non-differentiation induction group (No-diff) and a differentiation induction group (With-diff). The differentiation induction group (With-diff) did not undergo glycolic acid treatment. After incubation, the cells were returned to sebaceous gland culture medium and cultured for 6 days. After culturing, the medium was discarded, and the oil produced by sebaceous gland cells was stained with oil red stain (distributor: Cosmo Bio Co., Ltd.). The amount of oil droplets produced relative to the number of cells was evaluated. The results are shown in Figure 5. The glycolic acid addition group with a pH of 5.0 or higher exhibited a reduction in oil droplet production. 【0033】Next, after seeding human sebaceous cells, differentiation induction reagent (CTI) was added to a concentration of 0.1% by mass to induce differentiation. The cells were then cultured for 6 days in sebaceous gland medium containing 50 μM, 100 μM, and 1 mM glycolic acid, with the pH adjusted to 7.1. As controls, a non-differentiation-inducible group (No-diff) and a differentiation-inducible group (With-diff) were used. In these control groups, glycolic acid was not added, and the pH was set to 7.2. After culturing, the medium was discarded, and the oil produced by the sebaceous gland cells was stained with oil red stain (Cosmo Bio), and the amount of oil droplets produced relative to the number of cells was evaluated. The results are shown in Figure 4. It was shown that glycolic acid suppresses oil droplet production in a dose-dependent manner. 【0034】 Example 3: Examination of hydroxy acid types Human sebaceous gland cells collected from a 50-year-old woman were cultured in sebaceous gland culture medium (CTI). During subculturing, 2 × 10 ４ Cells were seeded in 24 plates at a cell / well ratio and cultured for 6 days at 37°C under a 5% CO2 atmosphere. Differentiation induction was induced by adding a differentiation induction reagent (CTI) to a concentration of 0.1% by mass. The culture was then replaced with sebaceous gland medium (CTI) containing 50 μM salicylic acid, 100 μM salicylic acid, 1 mM salicylic acid, 50 μM lactate, 100 μM lactate, 500 μM lactate, and 1 mM lactate, with the pH adjusted to near neutral, and cultured for 6 days. As controls, a non-differentiation induction group (No-diff) and a differentiation induction group (With-diff) were used. In these control groups, no hydroxy acids were added, and the pH was set to 7.2. After culture, the medium was discarded, and the oil produced by sebaceous gland cells was stained using oil red stain (distributor: Cosmo Bio), and the amount of oil droplets produced relative to the number of cells was evaluated. The results are shown in Figure 6. Salicylic acid, a C7 β-hydroxy acid, did not suppress oil droplet production, while lactic acid, a C3 α-hydroxy acid, was shown to suppress oil droplet production in a dose-dependent manner. 【0035】Example 4: Half-Face Test A double-blind half-face test was conducted on 31 female subjects aged 30-49 years, whose cheek sebum levels were measured using a Sebumeter (Courage + Khazaka electronic GmbH) and whose sebum levels were 30 AU or higher. The subjects' faces were divided into right and left halves, and the test solution was applied once daily to one half for eight weeks, while a placebo was applied to the other half. The test solution was a lotion base containing 4% glycolic acid, glycylglycine (appropriate amount), and niacinamide (appropriate amount), adjusted to pH 7.0. The placebo contained only the lotion base adjusted to pH 7.0. The pH of these test solutions was re-measured upon use and confirmed to fluctuate within the range of pH 6.5-7.5. Cheek sebum levels were measured using a Sebumeter (Courage + Khazaka electronic GmbH) at 4 and 8 weeks after the start of application (Figure 8A). A time-course comparison was performed using repeated measures ANOVA (**: p < 0.01, *: p < 0.05). A paired t-test with Bonferroni correction was used to compare the groups (†: p < 0.1). In the time-course comparison, the test solution group (Active) showed a significant decrease in sebum volume before application, and at 4 and 8 weeks. In the intergroup comparison between the test solution group (Active) and the placebo group (Placebo), the test solution group showed a decreasing trend in sebum volume at 8 weeks. In addition, replicas were created using the replica method, and the total pore area was measured using a confocal microscope (Figure 8B). Regarding the change over time, the Wilcoxon rank-sum signed test showed a significant decrease in total pore area between before application and 4 weeks in the test solution group (Active).

Claims

1. A topical skin composition comprising an α-hydroxy acid or a salt thereof having 6 or fewer carbon atoms, with a pH greater than 5.0 and 8.0 or less.

2. The topical skin composition according to claim 1, comprising 0.5% to 5% by mass of an α-hydroxy acid or a salt thereof.

3. The topical skin composition according to claim 1, wherein the α-hydroxy acid is at least one selected from the group consisting of glycolic acid, glyceric acid, tartonic acid, 2-hydroxybutyric acid, malic acid, tartaric acid, citric acid, and gluconic acid.

4. The topical skin composition according to claim 1, for use in suppressing sebum production.

5. The topical skin composition according to claim 1, for use in improving the appearance of enlarged pores and / or blackheads.

6. The topical skin composition according to claim 5 for reducing the size of enlarged pores.

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