JP2020109062A - Curly hair straightening method and hair treatment agent - Google Patents

Abstract

To provide a curly hair straightening method and a hair treatment agent that improve the shortcomings of curly hair straightening that are difficult handling of hair in an intermediate water washing step and a drying step and heat damage due to the drying step and an ironing step.SOLUTION: A curly hair straightening method has a step for reduction with a reductant, a step for hair reinforcing using levulinic acid, an intermediate water washing step, a drying step, an ironing step, a step for oxidation with an oxidizer, and a water washing step.SELECTED DRAWING: None

Description

The present invention also relates to a hair straightening method and a hair treatment agent which can reduce the handling of hair in the intermediate water washing step and the drying step, and can reduce the damage caused by heat in the drying step and the ironing step.

A general hair straightening agent can extend hair (suppress habit) by the action of reducing agents and oxidizing agents as main components and mechanical treatment at high temperature. Specifically, applying a first agent containing a reducing agent such as thioglycolic acid or a salt thereof, cysteamine or a salt thereof, and an alkaline agent such as aqueous ammonia, monoethanolamine, ammonium hydrogencarbonate, and arginine to hair. The disulfide bond existing in keratin protein is reductively cleaved, washed with intermediate water, dried with a drier, etc., and straightened by mechanical treatment at high temperature with an iron, and then oxidized with hydrogen peroxide or sodium bromate. It is treated with a second agent containing the agent as a main component to oxidize and reform disulfide groups and fix the hair straight. However, it is difficult to handle the hair during intermediate washing with water and drying with a drier, etc., and further, the hair becomes stiff and the feel deteriorates due to mechanical treatment at a high temperature by drying with a drier or the like, and heat damage occurs. There is a problem.

As a hair straightening method and a hair treatment agent with less heat damage, Patent Document 1 discloses a hair treatment method for straightening (hair straightening), a pretreatment agent, a first agent containing at least a reducing agent, and an intermediate treatment agent. A hair treatment agent containing an egg white hydrolyzate and an alkaline ionized water in a cosmetically acceptable treatment medium of at least one of a second agent containing at least an oxidizing agent and a post-treatment agent, The alkaline ionized water is electrolyzed water having a hydrogen ion concentration of pH 11 or more and an oxidation-reduction potential of 0 mV or less, and further has an osmotic pressure of 100 (mOsM) or less, and the hair treatment agent is arginine, At least one amino acid selected from the group consisting of lysine, histidine, citrulline, glycine, alanine, valine, isoleucine, leucine, phenylalanine, tyrosine, cysteine, methionine, proline, tryptophan, aspartic acid, glutamic acid, serine, threonine, and theanine, or taurine. A hair treatment method for treating hair using a hair treatment agent comprising: 1) diluting the hair treatment agent with the alkaline ionized water so that the content of the egg white hydrolyzate in the hair treatment agent is 1 To 4% by weight of the pretreatment agent to pretreat the hair, 2) dry at room temperature and then 3) with a first agent containing at least a reducing agent and 4) at least an oxidizing agent. Treatment with a second agent contained is disclosed. With this method, it is possible to improve the straight forming power and strengthen the hair, but it is not possible to sufficiently eliminate the fact that the hair becomes stiff and the feel is deteriorated due to heat damage.

As a hair straightening method with less heat damage and a hair treatment agent, Patent Document 2 discloses that a first agent treatment for a permanent wave, and 0.01 to 5.0 mass of a polymer substance that gels by heating after rinsing. It is disclosed that by using an intermediate treatment agent containing 100% of hair on the hair, hot air by a subsequent blowing operation and operation of a high-temperature iron are operated. In this method, a film can be formed on the surface of the hair by the hot air blow and the operation of a high-temperature iron, so that the hair can be protected from the hot air blow and the friction of the high-temperature iron operation. Even if you do not set the temperature of the high-temperature iron low, you can reduce the dryness and dustiness of the hair and reduce the damage to the cuticle, but it is enough that the hair becomes stiff and the feel deteriorates due to heat damage. It cannot be resolved.

As a hair straightening method with less heat damage, Patent Document 3 discloses (i) a step of applying a first agent containing a reducing agent, an alkaline agent and water to hair, and (i-2) washing the hair. Then, after the step of drying the hair, (i-3) water vapor is generated by boiling water in the boiler part of an atomizer provided with a boiler part and a handpiece part, and the steam is heated to 130° C. or higher and 3 atm. The above heating step, (i-4) superheating having a particle size of 0.26 to 1 nm and a temperature of 200 to 230° C. by reheating the water vapor to 200° C. or more in the handpiece part. A step of obtaining steam, (ii) a step of spraying the superheated steam toward the hair after the step (i-4), and (iii) a step of spraying the hair immediately after the spray or while performing the spray There is disclosed a method of applying straight perm to hair, which comprises the step of extending the hair by applying a temperature of 160 to 170°C. With this method, the hair is less damaged and the luster of the hair is further improved, but the present situation is that it is not practically useful because it requires labor and time, and/or a dedicated device for obtaining superheated steam.

Patent No. 6190796 JP 2005-89426 A Patent No. 6317515

The present invention has been made in view of the above-mentioned drawbacks of the prior art, and is a hair straightening method and a hair treatment method that can reduce the handling of hair in the intermediate water washing step and the drying step and reduce the heat damage due to the drying step and the ironing step. The purpose is to provide an agent.

The present inventor has conducted extensive studies to solve the above problems, and as a result, a reducing step using a reducing agent → a hair strengthening step containing levulinic acid → an intermediate washing step → a drying step → an ironing step → an oxidizing step using an oxidizing agent → washing with water The present invention has been completed by finding that the hair straightening method and the hair treatment agent characterized by comprising steps can reduce the difficulty of handling the hair in the intermediate washing step and the drying step and reduce the heat damage due to the drying step and the ironing step. Came to do. Although levulinic acid is known to have a pH adjusting action and is widely used in cosmetics, its effect of reducing damage due to heat has not been known.

That is, the hair straightening method and the hair treatment agent of the present invention are a reduction step of (1-1) applying a hair straightening first agent containing a reducing agent to the hair. (2-1) applying a hair treatment agent containing levulinic acid, a hair strengthening step, (3-1) rinsing and/or washing hair with hot water, an intermediate water washing step, and (3-2) drying with a dryer or the like A drying step, (3-3) straightening with a straight iron at 160 to 200° C., an ironing step, and (4-1) an oxidizing step of applying a second hair straightening agent containing an oxidizing agent. (5-1) Rinse with hot water and wash with water. It is characterized by comprising the reduction step, the hair strengthening step, the oxidation step, and the water washing step.

The curl straightening method and hair treatment agent of the present invention can reduce the handling of hair in the intermediate water washing step and the drying step and reduce the heat damage due to the drying step and the ironing step.

The curly straightening treatment method of the present invention essentially includes a hair strengthening step using a hair treatment agent containing levulinic acid. Hereinafter, the present invention will be described in detail.

(1-1) Applying the first curly hair straightening agent containing a reducing agent to the hair. The reducing step includes adjusting the content of the reducing agent, the pH, the alkalinity, and the time depending on the strength of the hair and the degree of damage. Set and reduce hair sufficiently.

(2-1) In the hair strengthening step of applying a hair treatment agent containing levulinic acid, the content of levulinic acid is 0.1 to 3.0% by weight, preferably 0, relative to the total amount of the hair treatment agent. It is 0.5 to 2.0% by weight. If it is less than 0.1% by weight, the coating amount becomes too large and it takes too much time. On the other hand, if it is more than 3.0% by weight, the curl straightening effect is lowered.

In addition to levulinic acid, other components commonly used in cosmetics, pharmaceuticals and the like can be optionally added to the hair treatment agent within a range that does not impair the effects of the present invention. Examples of such components include cationic polymers, anionic polymers, nonionic polymers, amphoteric polymers, polyhydric alcohols, sugars, amino acids, peptides, proteins, sequestering agents, oils, powder components, cationic interfaces. An activator, an anionic surfactant, a nonionic surfactant, an amphoteric surfactant, a pH adjuster, a thickener, a powder component, a fragrance, a powder component, a pigment, water and the like can be contained.

The dosage form of this hair treatment agent is not particularly limited as long as the desired effect is sufficiently exhibited, and for example, liquid, emulsion, gel, foam, cream, and other dosage forms can be adopted. It may be diluted with water before use.

(2-1) As a hair strengthening step of applying a hair treatment agent containing levulinic acid, it is desirable to apply 500 mL to 3,000 mL of a hair treatment agent evenly and sufficiently. The amount of application is determined by the width of the desired range for straightening the hair, the pH of the first hair straightening agent, and the alkalinity. (1-1) The residual alkali after the reduction step is neutralized (removed), and the swollen hair is gradually contracted. After that, levulinic acid further strengthens the hair. (3-1) Rinse and/or wash hair with hot water due to the strengthened hair. In the intermediate water washing step, the manageability of hair is improved, and (3-2) Straightening while drying with a dryer etc. In the arranging and drying steps, the manageability of hair is improved and the damage due to heat can be reduced. (3-3) Straightening is performed with a straight iron at 160 to 200°C. In the ironing step, straightening is performed. It is possible to reduce the damage caused by heat. The effect of levulinic acid for strengthening hair is due to the structure having a carbonyl group and a carboxyl group. Similarly, glyoxylic acid having a carbonyl group and a carboxyl group also has a hair-reinforcing effect, but it has a discoloring effect on hair color and is not suitable as a hair treatment agent for straightening hair.

(3-1) Rinse and/or wash hair with hot water, and thoroughly rinse away the hair straightening agent containing the first curl straightening agent and levulinic acid in an intermediate water washing step.
(3-2) Lightly wipe the water on the hair after washing with water, preferably dry it with a towel, and straighten it with a brush while drying it with a dryer, or prepare the hair with a surface temperature of 100 to 200°C. Alternatively, a drying step is performed in which the hair is straightened with a hair straightening iron and dried.
(3-3) An ironing process of straightening with a straight iron at 160 to 200°C. The temperature of the iron is adjusted according to the strength of the hair and the degree of damage.

(4-1) A second hair straightening agent containing an oxidizing agent is applied and sufficiently oxidized.

(5-1) Rinse with hot water and thoroughly wash away the second hair straightening agent in the washing step.

Further, before applying the hair treatment agent containing (2-1) levulinic acid, (2-1a) maleic acid is contained in an amount of 2.0 to 7.0% by weight, and the pH is 2.5 to 4.5. The hair-strengthening step may be performed in two stages by applying the hair treatment agent that is

The blending amount of maleic acid is 2.0 to 7.0% by weight, preferably 3.5 to 5.5% by weight, based on the total amount of the hair treatment agent. When the blending amount is less than 2.0% by weight, the effect of reducing the damage due to heat cannot be obtained. On the other hand, when the blending amount exceeds 7.0% by weight, the reduction of the damage due to heat corresponding to the blending amount is reduced. The improvement of the effect cannot be expected.

The hair treatment agent has a pH in the range of 2.5 to 4.5, preferably in the range of 3.0 to 4.0. If the pH is less than 2.5, the astringent effect of hair becomes strong and the effect of straightening hair cannot be improved, and if the pH exceeds 4.5, the astringent effect of hair becomes weak and the effect of straightening hair is reduced. Can not be obtained.
As the alkaline agent for adjusting the pH to the above range, inorganic bases such as sodium hydroxide and potassium hydroxide, organic bases such as triethanolamine and isopropanolamine, and basic amino acids, preferably monoethanolamine Primary amines can be used.

As another preferred component, (lanes 40-Na maleate/styrene sulfonic acid) copolymer may be added, and the blending amount is 0.2 to 1.5% by weight based on the total amount of the hair treatment agent of the present invention. , Preferably 0.5 to 1.0% by weight. If the blending amount is less than 0.2% by weight, the effect of reducing the damage due to heat and the improvement of the hair straightening effect cannot be obtained. On the other hand, if the blending amount exceeds 1.5% by weight, the blending amount is suitable. It cannot be expected that the heat damage reduction effect and the hair straightening effect will be improved.

In the hair treatment agent, in addition to maleic acid, a primary amine, and a (lanes 40-Na maleate/styrene sulfonic acid) copolymer, other components usually used in cosmetics, pharmaceuticals, etc. can be used. It can be optionally added within a range that does not impair it. Examples of such components include cationic polymers, anionic polymers, nonionic polymers, amphoteric polymers, polyhydric alcohols, sugars, amino acids, peptides, proteins, sequestering agents, oils, powder components, cationic interfaces. An activator, an anionic surfactant, a nonionic surfactant, an amphoteric surfactant, a pH adjuster, a thickener, a powder component, a fragrance, a powder component, a pigment, water and the like can be contained.

The dosage form of this hair treatment agent is not particularly limited as long as the desired effect is sufficiently exhibited, and for example, liquid, emulsion, gel, foam, cream, and other dosage forms can be adopted. It may be diluted with water before use.

Hereinafter, the present invention will be described in more detail with reference to specific examples, but the present invention is not limited to the following examples. Further, the compounding amount in the following examples and the like is shown by weight% unless otherwise specified.

(Examples 1-4 and Comparative Examples 1-2)
A hair treatment composition having the composition shown in Table 1 below was prepared by stirring and mixing each component in purified water until the components were uniform.
The ease of handling hair in the intermediate water washing step and the drying step of the hair straightening method and the hair treatment agent containing levulinic acid, and the effect of reducing heat damage due to the drying step and the ironing step were evaluated according to the following evaluation criteria.

<Evaluation of the manageability of hair, the degree of heat damage, and the straightening effect>
Natural curly hair (Indian black hair) was trimmed so that the length when extended was 15 cm, and a hair bundle having a weight of 3 g was prepared. Then, each hair bundle was washed with a commercially available shampoo, and then dyed twice with a commercially available 8-level brown hair color, and the moisture-removed hair bundle was used as a test hair bundle.
(1-1) Applying 8 mL of the first hair straightening agent containing thioglycolic acid and leaving for 10 minutes, reducing step, and (2-1) applying 50 mL of a hair treatment agent containing levulinic acid, hair strengthening step And (3-1) washing hair, intermediate washing step, (3-2) straightening with a brush while drying with a dryer, (3-3) straightening with a 180°C straight iron , Ironing process, (4-1) Apply 15 mL of second hair straightening agent containing hydrogen peroxide, leave for 8 minutes, oxidizing process, (5-1) Rinse with hot water, rinse with water, straighten Formed.
The manageability and feel of hair were evaluated according to the following evaluation criteria. In addition, the straightness effect was evaluated by the following evaluation criteria when the hair bundle was sufficiently wet and then left at room temperature for 24 hours in a hanging state and sufficiently dried. All evaluations were carried out by 3 people who have 10 years of experience as beauticians.

<Evaluation criteria for the manageability of hair>
(3-1) Washing hair, intermediate washing step, and (3-2) straightening with a brush while drying with a dryer, straightening and supple hair are easy to handle in the drying step.
1. Hair is difficult to handle 2. Hair is a little tricky 3. Hair is a little easier to handle 4. Easy to handle hair 5. Very easy to handle hair <Evaluation criteria for feel (comparison with untreated hair)>
The better the feel, the less the damage caused by heat.
1. Feel firmness 2. Feel a little firmness 3. 3. It feels a little stiff, but it doesn't bother you 4. Approximately the same feel, with almost no feeling of firmness 5. Equivalent or smooth feel without firmness <Straight effect evaluation criteria>
The straighter the effect, the higher the habit and the better the cohesion. There is still a habit and it is not well organized.
2. Some habits remain, and the unity is a little bad.
3. The habit is almost growing and the cohesion is good.
4. The habit has grown and the luster and cohesion are good.
5. The habit has grown and the luster and unity are very good.

As shown in Examples 1 to 4, when the hair strengthening step of applying a hair treatment agent containing levulinic acid was performed, sufficient manageability of the hair, feel and straight effect were obtained. On the other hand, as shown in Comparative Example 1, when the hair treatment agent containing levulinic acid was not applied and the hair strengthening step was not performed, the manageability and feel of the hair were insufficient. Further, as shown in Comparative Example 2, when the concentration of levulinic acid was out of the range, the feel and the straightening effect were insufficient.

(Example 5 and Comparative Examples 3 to 5)
A hair treatment composition having the composition shown in Table 2 below was prepared by stirring and mixing each component in purified water until the components were uniform.
The ease of handling the hair in the intermediate water washing step and the drying step of the hair straightening method and the hair treatment agent containing levulinic acid, and the effect of reducing the heat damage due to the drying step and the ironing step were evaluated according to the above evaluation criteria.

<Evaluation of the manageability of hair, degree of damage by heat, and straightening effect>
Natural curly hair (Indian black hair) was trimmed so that the length when stretched was 15 cm to prepare a hair bundle having a weight of 3 g. Then, each hair bundle was washed with a commercially available shampoo, and then dyed twice with a commercially available 8-level brown hair color, and the moisture-removed hair bundle was used as a test hair bundle.
(1-1) Applying 8 mL of the first hair straightening agent containing thioglycolic acid and leaving for 10 minutes, (2-1) Applying 50 mL of the hair treatment agent having the composition shown in Table 2 , Hair strengthening step, (3-1) washing hair, intermediate water washing step, (3-2) straightening with a brush while drying with a dryer, drying step, and (3-3) straight iron at 180°C Straightening, ironing process, (4-1) Apply 15 mL of second hair straightening agent containing hydrogen peroxide, leave for 8 minutes, oxidation process, (5-1) Rinse with hot water, rinse process Then, a straight was formed.

As shown in Example 5, when a hair strengthening step of applying a hair treatment agent containing levulinic acid was performed, sufficient manageability of the hair, feel and straight effect were obtained. On the other hand, as shown in Comparative Examples 3 to 5, in the case of the hair treatment agent containing an acid other than levulinic acid, the feel and the straightening effect were insufficient.

(Examples 6 to 14 and Comparative Examples 6 to 9)
A hair treatment composition having the composition shown in Table 1 below was prepared by stirring and mixing each component in purified water until the components were uniform.
The curl straightening method and the hair treatment agent containing levulinic acid, the hair treatment agent containing maleic acid in the intermediate water washing step and the drying step, and the effect of reducing the heat damage due to the drying step and the ironing step are as follows. It evaluated according to the evaluation criteria.

<Evaluation of the manageability of hair, the degree of damage due to heat, and the straightening effect>
Natural curly hair (Indian black hair) was trimmed so that the length when stretched was 15 cm to prepare a hair bundle having a weight of 3 g. Then, each hair bundle was washed with a commercially available shampoo, and then dyed twice with a commercially available 8-level brown hair color, and the moisture-removed hair bundle was used as a test hair bundle.
(1-1) Applying 8 mL of the first hair straightening agent containing thioglycolic acid and leaving for 10 minutes, reducing step, and (2-1a) applying 3 mL of the hair treatment agent containing maleic acid, the first step Hair strengthening step, (2-1) applying 50 mL of a hair treatment agent containing 1.5% of levulinic acid, second stage hair strengthening step, (3-1) washing hair, intermediate washing step, (3- 2) Drying process with a brush while straightening with a brush, (3-3) Straightening with a straight iron at 180°C, Ironing process, and (4-1) Hair straightening containing hydrogen peroxide. 15 mL of the second agent was applied and left for 8 minutes to form a straight line in the oxidation step, (5-1) rinsing with hot water, and the water washing step.

<Evaluation criteria for the manageability of hair>
Comparison with the case without the step (2-1a) 1. Hair becomes difficult to handle 2. Equivalent 3. Hair becomes a little easier to handle 4. 4. Easy to handle hair Very easy to handle hair <Evaluation criteria for feel>
Comparison with the case without the step (2-1a) 1. Harden 2. Equivalent 3. Further reduced hardness 4. Supple feel 5. Very supple feel <Evaluation criteria for straight effect>
Comparison with the case without the step (2-1a) 1. Reduced straight effect 2. Equivalent 3. 3. The straightening effect becomes slightly stronger. 4. The straightening effect becomes stronger 5. Straightening effect becomes stronger

As shown in Examples 6 to 14, when using a hair treatment agent in which maleic acid is adjusted to 2.0 to 7.0% by weight and the pH is adjusted to a range of 2.5 to 4.5, the hair is easily handled. And improved the touch and straightness effect. On the other hand, as shown in Comparative Examples 6 to 9, when the concentration and/or pH of maleic acid is out of the range, at least one or two or more of handleability and feel of hair and straight effect are obtained. The improvement was insufficient.

(Examples 15 to 23)
A hair treatment composition having the composition shown in Table 4 below was prepared by stirring and mixing each component in purified water until the components were uniform.
The hair straightening method and the hair treatment agent containing levulinic acid, the hair treatment agent containing maleic acid in the intermediate water washing step and the drying step, the ease of handling the hair, and the effect of reducing the heat damage due to the drying step and the ironing step are described above. It evaluated according to the evaluation criteria.

<Evaluation of the manageability of hair, the degree of heat damage, and the straightening effect>
Natural curly hair (Indian black hair) was trimmed so that the length when extended was 15 cm, and a hair bundle having a weight of 3 g was prepared. Then, each hair bundle was washed with a commercially available shampoo, and then dyed twice with a commercially available 8-level brown hair color, and the moisture-removed hair bundle was used as a test hair bundle.
(1-1) Applying 8 mL of the first hair straightening agent containing thioglycolic acid and leaving for 10 minutes, a reducing step, and (2-1a) applying 3 mL of a hair treatment agent containing maleic acid, the first step Hair strengthening step, (2-1) applying 50 mL of a hair treatment agent containing 1.5% levulinic acid, second stage hair strengthening step, (3-1) washing hair, intermediate washing step, (3- 2) straightening with a brush while drying with a dryer, (3-3) straightening with a straight iron at 180°C, ironing, and (4-1) straightening hair with hydrogen peroxide 15 mL of the second agent was applied and allowed to stand for 8 minutes, and an oxidation step, (5-1) rinsing with hot water, and a water washing step were used to form a straight.

As shown in Examples 15 to 23, when a hair treatment agent containing maleic acid in an amount of 2.0 to 7.0% by weight and a pH of 2.5 to 4.5 adjusted with monoethanolamine was used. , The handleability and feel of the hair and the straightening effect were improved.

(Examples 24 to 25 and Comparative Example 10)
A hair treatment composition having the composition shown in Table 5 below was prepared by stirring and mixing each component in purified water until the components were uniform.
Hair straightening method and hair treatment agent containing levulinic acid, hair treatment agent containing maleic acid and (lanes 40-Na maleate/styrene sulfonic acid) copolymer, easy handling and drying of hair in intermediate washing and drying steps. The effect of reducing the heat damage due to the step and the ironing step was evaluated according to the above evaluation criteria.

<Evaluation of the manageability of hair, the degree of damage due to heat, and the straightening effect>
Natural curly hair (Indian black hair) was trimmed so that the length when stretched was 15 cm to prepare a hair bundle having a weight of 3 g. Then, each hair bundle was washed with a commercially available shampoo, and then dyed twice with a commercially available 8-level brown hair color, and the moisture-removed hair bundle was used as a test hair bundle.
(1-1) Applying 8 mL of the first hair straightening agent containing thioglycolic acid and leaving for 10 minutes, a reducing step, and (2-1a) maleic acid and (lanes 40-Na maleic acid/styrene sulfonic acid). A first step hair strengthening step of applying 3 mL of a hair treatment agent containing a copolymer, and (2-1) a second step hair strengthening step of applying 50 mL of a hair treatment agent containing 1.5% of levulinic acid; -1) Washing hair, intermediate washing step, (3-2) straightening with a brush while drying with a dryer, drying step, and (3-3) straightening with a straight iron at 180°C, ironing step , (4-1) 15 mL of the second hair straightening agent containing hydrogen peroxide was applied and allowed to stand for 8 minutes, and an oxidation step and (5-1) rinsing with hot water and a water washing step were used to form a straight.

As shown in Examples 24 to 25, when the hair treatment agent to which the (Lanes 40-Na maleate/styrene sulfonic acid) copolymer is added is used, the manageability and feel of the hair and the improvement of the straightening effect are obtained. It was As shown in Comparative Example 10, when the concentration of (Lanes 40-Na maleate/styrene sulfonic acid) copolymer was out of the range, the manageability and feel of hair and the improvement of straightening effect were insufficient. ..

Claims (5)

(1-1) A reducing step of applying a curly straightening first agent containing a reducing agent to the hair. (2-1) applying a hair treatment agent containing levulinic acid, a hair strengthening step, (3-1) rinsing and/or washing hair with hot water, an intermediate water washing step, and (3-2) drying with a dryer or the like A drying step, (3-3) straightening with a straight iron at 160 to 200° C., an ironing step, and (4-1) an oxidizing step of applying a second hair straightening agent containing an oxidizing agent. (5-1) Rinse with hot water and wash with water. A method for straightening curly hair, which comprises the reducing step, the hair strengthening step, the oxidizing step, and the water washing step. The hair straightening treatment method according to claim 1, wherein the hair treatment agent applied in (2-1) contains levulinic acid in an amount of 0.1 to 3.0% by weight. (2-1) Before applying the hair treatment agent containing levulinic acid, (2-1a) contains maleic acid in an amount of 2.0 to 7.0% by weight and has a pH of 2.5 to 4.5. The method of straightening hair according to claim 1 or 2, wherein a hair treatment agent is applied and the hair strengthening step is performed in two steps. The hair straightening treatment method according to claim 3, wherein the component for adjusting the pH of the hair treatment agent containing maleic acid according to claim 3 to 2.5 to 4.5 is a primary amine. .. The hair treatment agent containing maleic acid according to claim 3 or 4, further comprising 0.2 to 1.5% of (lanes 40-Na maleate/styrene sulfonic acid) copolymer. Or the method for straightening hair according to item 4.