Skin cosmetics

Abstract

The purpose of the present invention is to provide a skin cosmetic that selectively removes free fatty acids and exhibits acne prevention effects without eliminating the moisture of the skin. The present invention relates to a skin cosmetic that is characterized by containing (A) a weak base and / or an amphoteric compound and (B) water and by having a pH of 8.5–9.5, the (A) weak base and / or amphoteric compound being at least one type of compound selected from compounds that have two acid dissociation constants (pKas).

Description

Technical Field

[0005]

[0001] The present invention relates to skin cosmetics. More specifically, it relates to skin cosmetics that can selectively remove free higher fatty acids involved in acne formation while appropriately leaving other sebum components on the skin, thereby cleaning the skin while maintaining a moist feeling.

Background Art

[0002] The main factors of acne include hypertrophy of sebaceous glands (excessive sebum secretion), hyperkeratosis of hair follicle pores, and the influence of bacteria (Non-Patent Document 1). In reality, these factors complexly interact with each other to worsen acne. Sebum (skin surface lipids) secreted from sebaceous glands contains cholesterol, squalene, free fatty acids, wax, triglyceride, etc. In particular, there is a report that the amount of fatty acids is increased in acne-prone skin (see Non-Patent Document 1, page 34, Figure 1-11).

[0003] In view of the above factors, in skin care considering acne prevention, it is recommended to keep the skin clean by washing, refrain from using highly oily cosmetics, pay attention to diet, and avoid stress and overwork.

[0004] However, when washing with conventional cleansing cosmetics, most of the above sebum components are washed away, resulting in the problem that the skin loses its moisture and becomes dry. In addition, sheet-like cosmetics of the type that wipe off dirt and old keratin on the skin instead of washing away sebum have been proposed (Patent Documents 1 and 2). However, no cosmetics that can selectively remove free fatty acids closely related to acne are known.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

[0006] [Non-Patent Document 1] "New Cosmetic Science," 2nd edition, edited by Takeo Mitsui, Nanzando, pp. 32-36) [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention aims to provide a skin cosmetic that selectively removes free fatty acids, which are thought to be involved in acne formation, from among the sebum components, and exhibits an acne-preventive effect without causing loss of skin moisture. [Means for solving the problem]

[0008] As a result of diligent research to solve the aforementioned problems, the present inventors have discovered that free fatty acids can be selectively removed by making the pH of the cosmetic alkaline by incorporating a weak base and / or an amphoteric compound, and have completed the present invention.

[0009] In other words, the present invention is (A) Weak bases and / or amphoteric compounds; and (B) Contains water, The pH is within the range of 8.5 to 9.5. The present invention provides a skin cosmetic characterized in that the (A) weak base and / or amphoteric compound is at least one selected from compounds having two acid dissociation constants (pKa). [Effects of the Invention]

[0010] The skin cosmetic of the present invention selectively removes free fatty acids from sebum components while leaving other sebum components on the skin, thus providing excellent acne prevention effects without losing skin moisture. Furthermore, because the cosmetic itself is alkaline, it also has the effect of smoothing the skin, similar to alkaline hot spring water. The skin cosmetic of the present invention can be washed off with water along with the fatty acids after application to the skin, or the fatty acids can be selectively removed by impregnating a sheet-like substrate with the cosmetic and wiping it off. [Modes for carrying out the invention]

[0011] (A) Weak bases and / or amphoteric compounds The skin cosmetic of the present invention (hereinafter also simply referred to as "cosmetic") contains (A) a weak base and / or an amphoteric compound (hereinafter also referred to as "component A") as an essential component. The (A) weak base and / or amphoteric compound in the present invention is at least one selected from compounds having two acid dissociation constants (pKa).

[0012] A "weak base" is generally defined as "a base that undergoes a small degree of protonation from a solvent, i.e., a base with a small base dissociation constant (Kb)" ("Comprehensive Dictionary of Chemistry," Tokyo Kagaku Dojin). In this invention, a "weak base" is an inorganic or organic compound generally known as a "weak base," and is a compound that has two acid dissociation constants (pKa). Therefore, triethanolamine (pKa=7.76), aminomethylpropanol (pKa=9.7), ammonium chloride (pKa=9.25), etc., which are weak bases but have only one pKa, are not included in component A of this invention.

[0013] Particularly preferred examples of the weak base of component A in the present invention include alkali metal bicarbonate (Na, K, etc.) salts, and among these, sodium bicarbonate (pKa(1)=6.4, pKa(2)=10.3).

[0014] Component A in the cosmetic of the present invention may be an amphoteric compound. Representative examples of the amphoteric compound include amino acids. Since an amino acid is an amphoteric compound containing an amino group and a carboxyl group in the molecule, it has at least two pKa values. Component A of the present invention is an amino acid having two pKa values, and does not include glutamic acid, aspartic acid, arginine, lysine, and histidine having three pKa values, even if it is an amino acid.

[0015] Examples of the amino acid used as the amphoteric compound of Component A of the present invention include amino acids having one amino group and one carboxyl group, such as glycine, alanine, glutamine, etc., and glycine (pKa(1)=2.35, pKa(2)=9.78) is particularly preferred.

[0016] As Component A of the cosmetic of the present invention, either one of the above-mentioned weak base and amphoteric compound (amino acid) may be used, or a mixture of both may be used.

[0017] The blending amount of Component A in the cosmetic of the present invention is 0.05 to 2.5% by mass, preferably 0.1 to 2.0% by mass. When Component A contains a weak base, it is particularly preferred to be within this range. On the other hand, when using an amphoteric compound, especially an amino acid, as Component A alone, it is preferable to adjust the blending amount to the range of 0.5 to 2.0% by mass.

[0018] The cosmetic of the present invention is an aqueous cosmetic in which the above-mentioned Component A is dissolved in (B) water. Therefore, water (also referred to as "Component B") as a base (medium) is an essential component.

[0019] The cosmetic of the present invention is an aqueous cosmetic containing the above-mentioned Component A and Component B, and having its pH within the range of 8.5 to 9.5. When blending an amphoteric compound (amino acid) alone as Component A, it is preferable to adjust the pH to the range of 8.5 to 8.8.

[0020] [[ID=2In the present invention, although pH adjustment is important, the adjustment method is not particularly limited. For example, an acidifying agent and / or a basifying agent conventionally used in cosmetics or the like may be added. Examples of the acidifying agent include hydrochloric acid, sulfuric acid, citric acid, etc., and examples of the basifying agent include sodium hydroxide, potassium hydroxide, etc.

[0021] By having the above-described configuration, the cosmetic of the present invention exhibits a novel effect (hereinafter referred to as "selective removal effect") of selectively removing free fatty acids among sebum components and leaving other sebum components on the skin. Due to this selective removal effect, the skin after being washed with the skin cosmetic of the present invention does not become too dry and has a smooth feeling while maintaining moisture.

[0022] In addition to the above essential components, the cosmetic of the present invention may contain other optional components usually used in skin cosmetics within a range that does not inhibit the effects of the present invention. Examples of other optional components include moisturizing components such as polyhydric alcohols, preservatives (or antibacterial agents) such as phenoxyethanol, lower alcohols having 1 to 6 carbon atoms such as ethanol, oil components, surfactants, powder components, various drugs, etc.

[0023] When a moisturizing component such as a polyhydric alcohol is blended in the cosmetic of the present invention, the moisture of the skin can be further improved. The polyhydric alcohol is not particularly limited, and examples thereof include glycerin, dipropylene glycol, polyethylene glycol, PEG / PPG dimethyl ether, etc. The blending amount of the polyhydric alcohol in the cosmetic of the present invention is not limited, but is 1 to 20% by mass, preferably 5 to 15% by mass.

[0024] Blending a preservative (or antibacterial agent) such as phenoxyethanol is preferable from the viewpoint of preventing acne, and the safety of the cosmetic of the present invention is maintained even when stored for a long period of time. Examples of the preservative (or antibacterial agent) include salicylic acid or its derivatives, benzalkonium chloride, etc. in addition to phenoxyethanol, and these may be blended in place of or in combination with phenoxyethanol. The amount of phenoxyethanol, etc., is 0.01 to 1% by mass, preferably 0.1 to 0.8% by mass.

[0025] Conventional skin cleansing cosmetics contain oils to dissolve and remove oily dirt, surfactants with cleansing effects (especially ionic surfactants), and powder components that have a scraping effect on dead skin cells, etc. The cosmetics of the present invention may contain these components, but from the viewpoint of leaving sebum components other than free fatty acids on the skin, it is preferable to keep the amounts of oils, surfactants, and powders to a minimum. Therefore, the skin cleansing cosmetics of the present invention include embodiments in which the amounts of oils, surfactants, and powders are 1% by mass or less, 0.5% by mass or less, or 0.1% by mass or less, respectively, and embodiments that do not contain any or all of the oils, surfactants, and powders.

[0026] The skin cosmetic of the present invention may be used as a cleansing cosmetic that is applied to the skin and washed off, or as a wipe-off type sheet skin cosmetic impregnated into a sheet-like substrate. Nonwoven fabric is preferably used as the sheet-like substrate. In either the wash-off type or the wipe-off type form, it is possible to selectively remove free fatty acids from sebum components.

[0027] Therefore, the present invention provides a skin cleansing method (washing method) that includes applying the skin cosmetic of the present invention to the skin and then rinsing with water, thereby selectively removing free fatty acids from sebum components. The present invention also provides a skin cleansing method that includes wiping the skin with a sheet-like skin cosmetic impregnated with the skin cosmetic of the present invention onto a sheet-like substrate, thereby selectively removing free fatty acids from sebum components. [Examples]

[0028] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, the amounts of the ingredients are expressed in mass percent.

[0029] <Method for evaluating selective removal effects> A pseudo-sebum composition having the following composition was prepared (hereinafter referred to as "artificial sebum").

[0030] [Table 1]

[0031] (1) 0.9 mg of the above artificial sebum was spread on a 30 mm square piece of aluminum foil (using a finger cot) and stored at 37°C for 30 minutes. (2) Spread 18 μL of the cosmetic product described below onto the aluminum foil from (1) (using a finger cot). (3) Immediately after applying the cosmetic in (2), rinse with deionized water (500 mL) for 15 seconds. (4) The aluminum foil from (3) was dried in a constant temperature bath at 37°C for 1.5 hours, and the substance remaining on the surface of the aluminum foil was analyzed and quantified by IR.

[0032] From the IR measurement results obtained in step (4) above, the "amount of artificial sebum remaining on the aluminum foil," the "amount of oleic acid remaining on the aluminum foil," and the "percentage of the amount of remaining oleic acid relative to the amount of artificial sebum remaining on the aluminum foil" were calculated, and the following parameters (A), (B), and (C) were calculated.

[0033] (A) Artificial sebum retention rate (["Amount of artificial sebum remaining on aluminum foil" / "Amount of artificial sebum initially applied (0.9 mg)"] × 100) (B) Oleic acid retention rate (["Amount of oleic acid remaining on the aluminum foil" / "Amount of oleic acid contained in the artificial sebum initially applied (0.162 mg)"] × 100) (C) Selective removal effect ([1 - ("Ratio of the amount of remaining oleic acid to the amount of artificial sebum remaining on the aluminum foil (%)" / 18%)) × 100)

[0034] Parameter (A) above indicates the cleansing effect on sebum as a whole. A small value for (A) means that (while it has a good general cleansing effect) too much sebum is removed, leading to a loss of skin moisture. Parameter (B) indicates the effect of removing oleic acid (free fatty acid). Parameter (C) indicates the degree to which oleic acid is selectively removed from the sebum components.

[0035] In this invention, the requirements for a cosmetic composition that does not remove too much of the sebum as a whole, and is excellent in removing free fatty acids (oleic acid) that cause acne (i.e., has excellent selective removal effect) were set as (A) ≥ 30%, (B) < 50%, and (C) ≥ 35%.

[0036] Skin cosmetics were prepared using the formulations listed in Tables 2 and 3 below. For each cosmetic, the selective removal effect on free fatty acids was evaluated according to the method described above.

[0037] [Table 2]

[0038] [Table 3]

[0039] As shown in Table 2, the cosmetic composition of Comparative Example 1, which did not contain component A of the present invention, was insufficient in both overall sebum removal and selective removal of oleic acid. A similar trend was observed in Comparative Example 2, which had a pH of less than 8.5 even with the inclusion of sodium bicarbonate. On the other hand, Examples 1 to 3, which contained sodium bicarbonate and had a pH in the range of 8.5 to 9.5, were able to selectively remove oleic acid without excessively removing sebum.

[0040] Table 3 shows that Comparative Examples 3-5, which contained weak bases that do not correspond to component A of the present invention, did not exhibit a selective removal effect of oleic acid, even though the pH range conditions were met. On the other hand, Example 4, which contained glycine, an amino acid (amphoteric compound), and also met the pH requirements, was able to selectively remove oleic acid without excessively removing sebum. However, Comparative Example 6, which contained the same amount of the same amino acid but whose pH was outside the specific range of the present invention, did not show a selective removal effect on oleic acid.

Claims

1. (A) Weak bases or amphoteric compounds; and (B) Contains water, If a weak base is included, the weak base is an alkali metal bicarbonate, the amount of the weak base is 0.1 to 2.0% by mass, and the pH is in the range of 8.5 to 9.

5. If an amphoteric compound is included, the amphoteric compound is glycine, the amount of glycine is 0.5 to 2.0% by mass, and the pH is in the range of 8.5 to 8.

8. A skin cosmetic characterized by not containing surfactants.

2. The skin cosmetic according to claim 1, wherein the alkali metal bicarbonate salt is sodium bicarbonate.

3. A skin cosmetic composition according to claim 1 or 2, further comprising a polyhydric alcohol.

4. A skin cosmetic according to any one of claims 1 to 3, further comprising phenoxyethanol.

5. A skin cosmetic composition according to any one of claims 1 to 4, which does not contain oil.

6. A sheet-type skin cosmetic characterized by impregnating a sheet-type substrate with the skin cosmetic described in any one of claims 1 to 5.

7. The sheet-like skin cosmetic according to claim 6, wherein the sheet-like base material is made of a nonwoven fabric.

8. A method for cleansing the skin, characterized by applying the skin cosmetic according to any one of claims 1 to 5 to the skin, and then rinsing with water.

9. A method for cleansing the skin, characterized by wiping the skin with the sheet-like skin cosmetic described in claim 6 or 7.

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