cosmetics
Article Research on Hair Bleach that Causes Less Hair Damage and Smells Less Pungent than Ammonium Hydroxide
Kyouhei Igarashi 1 and Kazuhisa Maeda 1,2,* ID
1 Bionics Program, Tokyo University of Technology Graduate School, Tokyo 192-0982, Japan; [email protected] 2 School of Bioscience and Biotechnology, Tokyo University of Technology, Tokyo 192-0982, Japan * Correspondence: [email protected]; Tel.: +81-42-6372442
Received: 20 May 2018; Accepted: 19 June 2018; Published: 20 June 2018
Abstract: Problems associated with bleaching hair include damage to the hair and the pungent smell of ammonium hydroxide. Many consumers dislike the stiffness and smell of bleached hair. In this study, we investigated the suppression of both the damage and pungent smell of bleach by using an aqueous solution of 2-amino-2-methyl-1,3-propanediol (AMPD) as an alkaline agent. The test results focused on scanning electron microscope observations, antioxidant activity and protein loss, and showed that the use of AMPD aqueous solution as an alkaline agent suppressed both hair damage and undesirable odor compared with the use of ammonium hydroxide. AMPD aqueous solution is considered more useful than ammonium hydroxide as an alkaline agent in the hair-bleaching process.
Keywords: hair bleach; cuticle; 2-amino-2-methyl-1,3-propanediol
1. Introduction Melanin is a polyphenol-like macromolecule composed primarily of 5,6-dihydroxyindole (DHI) and 5,6-dihydroxyindole-2-carboxylic acid (DHICA) units. Some hair eumelanins contain more DHICA than DHI. On the other hand, blond hair contains pheomelanin (composed of benzothiazine units) rather than dihydroxyindoles [1]. Ordinarily, the removal of melanin coloring from hair through bleaching begins with treatment with an alkaline agent, followed by treatment with an oxidizing agent. In many commercial types of bleach, ammonium hydroxide is used as the alkaline agent, and hydrogen peroxide is employed as the oxidizing agent. The proposed mechanism suggests that under alkaline conditions, hydrogen peroxide produces HOO−, which undergoes a nucleophilic addition to the carbonyl carbon of the catechol in melanin. The melanin catechol is cleaved, and the melanin structure undergoes oxidative degradation [2]. However, the bleaching process damages hair [3–8]. The purpose of this study was to evaluate what changes occur in hair damage when ammonium hydroxide, used in the first treatment step, is replaced by another alkaline agent. The present study focused on 2-amino-2-methyl-1,3-propanediol (AMPD; Figure1) as a replacement for ammonium hydroxide. Hair bleached with AMPD aqueous solution and hydrogen peroxide was evaluated by color analysis, scanning electron microscope observations, oxidation tests, and protein loss tests [9–11]. It was noted that hair that was bleached with AMPD aqueous solution showed outstanding decoloration, low antioxidant activity and low protein loss and cuticle damage compared with hair that was bleached using ammonium hydroxide. This suggests that a bleaching process using AMPD aqueous solution minimizes damage to the hair compared with previous ammonium hydroxide-based processes for melanin decoloration. Studies of the hair bleaching effect of hydrogen peroxide using either ammonium hydroxide or AMPD aqueous solution as an alkaline agent demonstrated that AMPD
Cosmetics 2018, 5, 39; doi:10.3390/cosmetics5020039 www.mdpi.com/journal/cosmetics Cosmetics 2018, 5, x FOR PEER REVIEW 2 of 10 Cosmetics 2018, 5, 39 2 of 10
of hydrogen peroxide using either ammonium hydroxide or AMPD aqueous solution as an alkaline aqueousagent demonstrated solution is more that useful AMPD as anaqueous alkaline solution agent than is ammoniummore useful hydroxide as an alkaline based on agent the results than ofammonium hair color, hydroxide field emission based scanning on the results electron of microscopehair color, field (FE-SEM) emission observations, scanning electron antioxidant microscope activity and(FE-SEM) protein observations, loss. antioxidant activity and protein loss.
Figure 1. Chemical structure of 2-amino-2-methyl-1,3-propanediol (AMPD). Figure 1. Chemical structure of 2-amino-2-methyl-1,3-propanediol (AMPD).
AMPD is an aliphatic dihydric alcohol derivative and is used as a pH pH regulator regulator in in cosmetics cosmetics [12]. [12]. It permeatespermeates into into hair hair and and has has a moisturizing a moisturizing effect. effect. In cosmetics, In cosmetics, it is included it is included in a variety in a of variety products, of includingproducts, including toilet water, toilet lotions water, and lotions sunscreens. and sunscreens. It is essentially It is essentially odorless odorless on its own, on its and own, the and smell the becomessmell becomes imperceptible imperceptible when dissolved when dissolved in water; therefore,in water; it therefore, addresses theit addresses concerns ofthe customers concerns who of dislikecustomers pungent who dislike smells. pungent smells.
2. Materials and Methods
2.1. Materials 2.1. Materials Hydrogen peroxide (35%), ethanol, ammonium hydroxide (28%), hydrochloric acid (20%), Hydrogen peroxide (35%), ethanol, ammonium hydroxide (28%), hydrochloric acid (20%), L-(+)- Lascorbic-(+)-ascorbic acid sodium acid sodium salt, sodium salt, sodium disulfite, disulfite, 1,1-di 1,1-diphenyl-2-picrylhydrazylphenyl-2-picrylhydrazyl (DPPH), (DPPH), zinc acetate, zinc acetate, iron iron(III) (III)chloride chloride hexahydrate hexahydrate and and sodium sodium hydroxide hydroxide were were purchased purchased from from Wako Wako Pure Pure ChemicalChemical Industries, Ltd. (Osaka, Japan).Japan). The reagents used were guaranteed reagents of JapaneseJapanese IndustrialIndustrial Standards (JIS)(JIS) grade.grade. 2-Amino-2-methyl-1,3-propanediol was purchased from Tokyo Tokyo Chemical Industry, Ltd. (Tokyo, (Tokyo, N N p Japan).Japan). N, ,N-Dimethyl--Dimethyl-p-phenylenediamine-phenylenediamine dihydrochloride dihydrochloride was was purchased purchase fromd from Sigma-Aldrich Sigma-Aldrich Corp. (St. Louis, MO, USA). BCATM Protein Assay Kit—reducing agent-compatible was purchased from Corp. (St. Louis, MO, USA). BCATM Protein Assay Kit—reducing agent-compatible was purchased Thermofrom Thermo Fisher Fisher Scientific Scientific Inc. (Waltham, Inc. (Waltham, MA, USA).MA, USA). Phosphate-buffered Phosphate-buffered saline saline (PBS) (PBS) tablets tablets were purchasedwere purchased from Takarafrom Takara Bio Inc. Bio (Shiga, Inc. (Shiga, Japan). Japan). 2.2. Comparison of Smell and Human Hair Bleaching Results Using 2-amino-2-methyl-1,3-propanediol (AMPD)2.2. Comparison Aqueous of SolutionSmell and or Human Ammonium Hair HydroxideBleaching Results as an Alkaline Using 2-amino-2-methyl-1,3-propanediol Agent (AMPD) Aqueous Solution or Ammonium Hydroxide as an Alkaline Agent Pungent smell was evaluated in five grades by three expert evaluators. Comparison of human hair bleachingPungent smell study was employed evaluated hair in from five Japanese grades by men three in their expert 20s evaluators. that had not Comparison hitherto been of exposed human tohair chemical bleaching treatment. study employed The reagents hair used from were Japanese 30% hydrogen men in peroxide, their 20s 10% that AMPD had not aqueous hitherto solution, been andexposed 25% to ammonium chemical treatment. hydroxide. The Decolorization reagents used was were not 30% complete hydrogen at 30 peroxide, and 60 min; 10% therefore, AMPD aaqueous 90 min experimentsolution, and was 25% performed. ammonium The AMPDhydroxide. aqueous Decolorization solution and was ammonium not complete hydroxide at 30were and adjusted60 min; totherefore, pH 10.75. a 90 Samples min experiment of 200 mg ofwas hair performed. were weighed The outAMPD and thenaqueous immersed solution for and 90 minammonium at room temperaturehydroxide were in one adjusted of the followingto pH 10.75. solutions: Samples tap of water 200 usedmg of as hair a control, were aweighed mixed solutionout and ofthen 8% hydrogenimmersed peroxidefor 90 min and at 2% room AMPD, temperature or a mixed in solution one of the of 8% following hydrogen solutions: peroxide tap and water 5% ammonium used as a hydroxide.control, a mixed The hair solution was then of removed8% hydrogen from the pero mixedxide solutionsand 2% andAMPD, thoroughly or a mixed washed solution several of times 8% inhydrogen tap water. peroxide and 5% ammonium hydroxide. The hair was then removed from the mixed solutions and thoroughly washed several times in tap water. 2.3. Gloss Meter Measurement of Human Hair Glossiness Following Treatment with AMPD Aqueous Solution or2.3. Ammonium Gloss Meter Hydroxide Measurement as an of Alkaline Human Agent Hair Glossiness Following Treatment with AMPD Aqueous Solution or Ammonium Hydroxide as an Alkaline Agent The gloss meter measures the glossiness of a sample by measuring the quantity of light reflected off the sample.The gloss The meter gloss measures of a surface the can glossiness be represented of a samp as thele by quantity measuring of light the incident quantity on of the light surface reflected that isoff directly the sample. reflected. The gloss Parallel of a whitesurface light can isbe emitted represen byted the as probe the quantity head at of an light angle incident of 60◦ onto thethe surface tothat be is measured. directly reflected. A portion Parallel of this lightwhite is reflectedlight is emitted directly by at the sameprobe angle, head andat an a portionangle of is 60° scattered to the orsurface reflected to be after measured. being adsorbed A portion by of thethis surface. light is re Theflected Skin-Glossymeter directly at the GL200same angle, (Courage and a + portion Khazaka is Electronicscattered or GmbH, reflected Köln, after Germany) being adsorbed measures by both the directly surface. reflected The Skin-Glossymeter light (reflection GL200 channel) (Courage and light + Khazaka Electronic GmbH, Köln, Germany) measures both directly reflected light (reflection
Cosmetics 2018, 5, 39 3 of 10 from the surface associated with gloss and scattering (diffuse channel). The Skin-Glossymeter GL200 is designed specifically for evaluating the gloss of skin and hair. Although the structure, brightness and color of skin and hair are different, the gloss of different skin types and hair colors can be easily measured with high precision as these differences are accounted for and essentially eliminated by a scattering correction.
2.4. Measurement of the Antioxidant Activity of Human Hair after Using AMPD Aqueous Solution or Ammonium Hydroxide as an Alkaline Agent Samples of 30 mg of hair added to 300 µL of a 150 µmoL/L DPPH-ethanol solution and 300 µL of pure water, 30 mg of hair added to 300 µL of ethanol and 300 µL of pure water, and 300 µL of pure water added to 300 µL of a 150 µmoL/L DPPH-ethanol solution were prepared, and absorbance (517 nm) measurements were taken after 30 min of treatment using a microplate reader (Multi-Detection Microplate POWERSCAN HT; BioTek, Winooski, VT, USA). The absorbance of 30 mg of hair added to 300 µL of a 150 µmoL/L DPPH-ethanol solution and 300 µL of pure water was used as the absorbance of each sample solution (A), the absorbance of 30 mg of hair added to 300 µL of ethanol and 300 µL of pure water was used as the absorbance blank of each sample solution (B), and the absorbance of 300 µL of pure water added to 300 µL of a 150 µmoL/L DPPH-ethanol solution was used as the absorbance of the control solution (C). DPPH radical elimination was confirmed based on the deep violet color of DPPH. DPPH radical elimination = {C − (A − B)}/C × 100 (%).
2.5. Determination of Relative Protein Loss from Human Hair on Which AMPD Aqueous Solution or Ammonium Hydroxide was Used as an Alkaline Agent The protein concentration in the solution of each 100 mg of hair treated with or without an alkaline component was determined. The amount of protein that eluted from the hairs in the solution after the bleaching experiment was measured using a BCA protein assay kit. Reagents A and B were mixed at 50:1, and 1 µL of the post-bleaching solution was added to 99 µL of the mixed solution and incubated at 37 ◦C for 30 min. Absorbance (562 nm) was measured using the microplate reader to determine the relative quantities.
2.6. Detection of Thiol Group (–SH) Concentration Produced by Disulfide Bond Cleavage in Human Hair after Using AMPD Aqueous Solution or Ammonium Hydroxide as an Alkaline Agent Each 100 mg hair sample was treated with or without alkaline agents (800 µL). After 24 h, the solutions were recovered and centrifuged for 5 min, and 200 µL of supernatant was collected. Six hundred microliters of 1% aqueous zinc acetate was added, the mixture was centrifuged for 5 min, and the supernatant was discarded. This procedure was used to precipitate the hydrogen sulfide ions as zinc sulfide. One milliliter of pure water was added, and the precipitate was suspended by vortexing and pipetting; it was then centrifuged for 5 min, and the supernatant was discarded. This washing procedure was carried out a total of three times. The supernatant was then discarded, and 200 µL of pure water was added. The precipitate was suspended; 50 µL of a 20 mmoL/L N,N-dimethyl-p-phenylenediamine dihydrochloride solution and 50 µL of a 30 mmoL/L FeCl3 solution were added, followed by vortexing and incubation for 30 min at room temperature. After centrifugation, 100 µL aliquots of the supernatant were added to the wells of three 96-well plates, and the absorbance (665 nm) measurements were taken using the microplate reader. The concentration of hydrogen sulfide ions generated by the reduction of thiol groups (–SH), which were produced by cleavage of disulfide bonds in human hair, was calculated.
2.7. Field Emission Scanning Electron Microscope (FE-SEM) Observations on Human Hair Following the Use of AMPD Aqueous Solution or Ammonium Hydroxide as an Alkaline Agent Each hair sample was cut to a length of approximately 2 mm and fixed on the sample stand. Platinum coating was carried out four times at 20 s intervals and was followed by standing for one day Cosmetics 2018, 5, 39 4 of 10 under vacuum. The samples were then observed using a field emission scanning electron microscope and energy-dispersive X-ray spectroscopy (EDS, JEOL Ltd., Tokyo, Japan).
Cosmetics 2018, 5, x FOR PEER REVIEW 4 of 10 2.8. Oxygen Mapping of Human Hair by Energy-dispersive X-ray Spectroscopy (EDS) Following the Use of AMPDday Squeous under Solution vacuum. or The Ammonium samples were Hydroxide then observ as aned Alkaline using Agenta field emission scanning electron microscope and energy-dispersive X-ray spectroscopy (EDS, JEOL Ltd., Tokyo, Japan). Oxygen mapping by EDS was carried out for 70 min on the surface of the hair samples produced for FE-SEM.2.8. Oxygen Mapping of Human Hair by Energy-dispersive X-ray Spectroscopy (EDS) Following the Use of AMPD Squeous Solution or Ammonium Hydroxide as an Alkaline Agent 2.9. Statistical Analysis Oxygen mapping by EDS was carried out for 70 min on the surface of the hair samples produced Meanfor FE-SEM. values and standard deviations were calculated, and unpaired t-tests were carried out using Microsoft Excel. Evaluation: +: p < 0.1 was taken as a tendency; *: p < 0.05, **: p < 0.01, ***: p < 0.001, 2.9. Statistical Analysis and ***: p < 0.0001 were taken to be significant differences. Mean values and standard deviations were calculated, and unpaired t-tests were carried out 3. Resultsusing Microsoft Excel. Evaluation: +: p < 0.1 was taken as a tendency; *: p < 0.05, **: p < 0.01, ***: p < 0.001, and ***: p < 0.0001 were taken to be significant differences. 3.1. Comparison of Smell and Appearance When AMPD Aqueous Solution or Ammonium Hydroxide Was Used as3. an Results Alkaline Agent for Dyeing Human Hair
The3.1. odor Comparison of ammonia of Smell and was Appearance apparent When when AM ammoniumPD Aqueous Solution hydroxide or Ammonium was used Hydroxide as an alkalineWas agent, but whenUsed AMPD as an Alkaline aqueous Agent solutionfor Dyeing wasHuman used, Hair there was no noticeable smell. The appearance was also transparent.The odor of ammonia was apparent when ammonium hydroxide was used as an alkaline agent, Figurebut when2 shows AMPD images aqueous of solution a bundle was of used, human there hair was no immersed noticeable in smell. pure The water appearance (control), was aalso bundle of transparent. human hair bleached with H2O2 and AMPD aqueous solution, and a bundle of human hair bleached Figure 2 shows images of a bundle of human hair immersed in pure water (control), a bundle of with H2O2 and ammonium hydroxide. The various images were taken with a digital camera, a BX51 human hair bleached with H2O2 and AMPD aqueous solution, and a bundle of human hair bleached upright optical microscope (Olympus Corp., Tokyo, Japan) and BP72 microscope digital camera with H2O2 and ammonium hydroxide. The various images were taken with a digital camera, a BX51 (Olympusupright Corp., optical Tokyo, microscope Japan). (Olympus It is evident Corp., thatTokyo, the Japan) hair bundleand BP72 bleached microscope using digital AMPD camera aqueous solution(Olympus as the alkaline Corp., Tokyo, agent Japan). shows It moreis evident intense that decolorationthe hair bundlethan bleached the hairusing bundle AMPD aqueous bleached using ammoniumsolution hydroxide. as the alkaline agent shows more intense decoloration than the hair bundle bleached using ammonium hydroxide.
FigureFigure 2. Images 2. Images of human of human hair hair bleached bleached with with H2 HO22 andO2 2%and AMPD 2% AMPD aqueous aqueous solution and solution human andhair human bleached with H2O2 and 5% ammonium hydroxide. The experimental conditions are described in hair bleached with H2O2 and 5% ammonium hydroxide. The experimental conditions are described in SectionSection 2.2.(Above 2.2. (Above) Images) Images taken taken with with a a digital digital camera camera of ofsame same person’s person’s hairs; hairs; (Below (Below) images) imagestaken taken with an optical microscope. Top: human hair bundle immersed in pure water (control); middle: with an optical microscope. Top: human hair bundle immersed in pure water (control); middle: human human hair bundle bleached with H2O2 and AMPD aqueous solution; bottom: human hair bundle hair bundlebleached bleached with H2O with2 and H ammonium2O2 and AMPD hydroxide. aqueous solution; bottom: human hair bundle bleached with H2O2 and ammonium hydroxide. Cosmetics 2018, 5, 39 5 of 10
Cosmetics 2018, 5, x FOR PEER REVIEW 5 of 10 3.2. Comparison of Gloss Meter Measurements of Human Hair after Using AMPD Aqueous Solution or Ammonium3.2.Cosmetics Comparison Hydroxide2018, 5, x ofFOR Gloss as PEER an Meter AlkalineREVIEW Measurements Agent of Human Hair after Using AMPD Aqueous Solution or5 of 10 Ammonium Hydroxide as an Alkaline Agent Figure3.2. Comparison3 shows of the Gloss results Meter of Measurements the Glossymeter of Human measurements Hair after Using (quantity AMPD Aqueous of directly Solution reflected or light) Figure 3 shows the results of the Glossymeter measurements (quantity of directly reflected light) of a humanAmmonium hair Hydroxide bundle as immersed an Alkaline Agent in pure water (control), a human hair bundle bleached with of a human hair bundle immersed in pure water (control), a human hair bundle bleached with H2O2 H2O2 and AMPD aqueous solution, and a human hair bundle bleached with H2O2 and ammonium and AMPDFigure 3aqueous shows the solution, results of and the Glossymetera human hair meas bundleurements bleached (quantity with of H directly2O2 and reflected ammonium light) hydroxide. The gloss measurement was higher for hair bleached using AMPD aqueous solution than hydroxide.of a human The hair gloss bundle measurement immersed inwas pure higher water for (control), hair bleached a human using hair AMPD bundle aqueous bleached solution with Hthan2O2 for hairforand hair bleached AMPD bleached aqueous using using ammonium solution, ammonium and hydroxide. hydroxide. a human hair bundle bleached with H2O2 and ammonium hydroxide. The gloss measurement was higher for hair bleached using AMPD aqueous solution than for hair bleached using ammonium hydroxide.
FigureFigure 3. Comparison 3. Comparison of of the the gloss gloss measurements measurements of of a a human human hair hair bundle bundle immersed immersed in pure in purewater water
(control),(control), a human a human hair hair bundle bundle bleachedbleached with with H2 HO22 Oand2 and 5% ammonium 5% ammonium hydroxide, hydroxide, and a human and ahair human hairbundle Figure bleached3. bleached Comparison with with H of2O the H2 and2 Ogloss2 2%and measurementsAMPD 2%AMPD aqueous of aqueous solution. a human solution.The hair results bundle Theare immersed expressed results in are as pure the expressed meanwater as the mean±(control), standard± standard a deviationhuman deviationhair of fivebundle experiments. of bleached five experiments. with *** p H< 20.001,O2 and *** **** 5%p
Figure 4. Comparison of the 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical-eliminating capacity of
human hair immersed in pure water (control), human hair bleached with H2O2 and 5% ammonium Figurehydroxide,Figure 4. Comparison 4. Comparison and human of theofhair the 1,1-diphenyl-2-picrylhydrazyl bleached 1,1-diphenyl-2-picrylhydr with H2O2 and 2%azyl AMPD (DPPH) (DPPH) aqueous radical-eliminating radical-eliminating solution. The capacityresults capacity are of of
humanexpressedhuman hair hair immersed as immersedthe mean in ± purein standard pure water water deviation (control), (control), of fifteen humanhuman experiments. hair bleached bleached * p with< with0.05, H 2** HO p2 O and< 20.01.and 5% ammonium 5% ammonium hydroxide, and human hair bleached with H2O2 and 2% AMPD aqueous solution. The results are hydroxide, and human hair bleached with H2O2 and 2% AMPD aqueous solution. The results are expressedexpressed as the as meanthe mean± standard± standard deviation deviation of fifteen fifteen experiments. experiments. * p*
Cosmetics 2018, 5, 39 6 of 10
Cosmetics 2018, 5, x FOR PEER REVIEW 6 of 10 3.4. Comparison of Quantities of Protein Lost From Human Hair after Treatment with AMPD Aqueous SolutionCosmetics3.4. orComparison Ammonium 2018, 5, x FORof Quantities HydroxidePEER REVIEW of asProtein an Alkaline Lost From Agent Human Hair after Treatment with AMPD Aqueous6 of 10 Solution or Ammonium Hydroxide as an Alkaline Agent Figure3.4. Comparison5 compares of Quantities the quantities of Protein of proteinLost From lost Human from Hair human after hairTreatment immersed with AMPD in pure Aqueous water (control), humanSolution hairFigure bleachedor Ammonium 5 compares with Hydr Hthe2oxideO 2quantitiesand as an AMPD Alkaline of protein aqueous Agent lost solution, from human and humanhair immersed hair bleached in pure withwater H 2O2 (control), human hair bleached with H2O2 and AMPD aqueous solution, and human hair bleached and ammoniumFigure 5 hydroxide. compares the After quantities bleaching of protein human lost hair from using human ammonium hair immersed hydroxide, in pure the quantitywater of with H2O2 and ammonium hydroxide. After bleaching human hair using ammonium hydroxide, the protein(control), eluted human from the hair hair bleached in the with solution H2O2was and 67.4AMPDµg/mg aqueous hair, solution, whilethe and quantity human hair of protein bleached eluted quantity of protein eluted from the hair in the solution was 67.4 μg/mg hair, while the quantity of fromwith the hair H2O present2 and ammonium in the solution hydroxide. after After using bleaching AMPD aqueoushuman hair solution using ammonium was 40.4 µ g/mghydroxide, hair. the Protein protein eluted from the hair present in the solution after using AMPD aqueous solution was 40.4 loss wasquantity halved of protein by using eluted AMPD from the aqueous hair in solutionthe solution as anwas alkaline 67.4 μg/mg agent hair, compared while the withquantity the of use of μg/mg hair. Protein loss was halved by using AMPD aqueous solution as an alkaline agent compared protein eluted from the hair present in the solution after using AMPD aqueous solution was 40.4 ammoniumwith the hydroxide. use of ammonium hydroxide. μg/mg hair. Protein loss was halved by using AMPD aqueous solution as an alkaline agent compared with the use of ammonium hydroxide.
FigureFigure 5. Determination 5. Determination of of quantities quantities of ofprotein protein lost from human human hair hair after after using using 5% 5%ammonium ammonium hydroxidehydroxide or 2% or AMPD2% AMPD aqueous aqueous solution solution as as an an alkalinealkaline agent. agent. The The re resultssults are are expressed expressed as the as mean the mean Figure 5. Determination of quantities of protein lost from human hair after using 5% ammonium ± ± standard deviation of three experiments. *** p < 0.001, **** p < 0.0001. standardhydroxide deviation or 2% AMPD of three aqueous experiments. solution as *** anp alkaline< 0.001, agent. **** p The< 0.0001. results are expressed as the mean ± standard deviation of three experiments. *** p < 0.001, **** p < 0.0001. 3.5. Concentration of Thiol Groups (-SH) Produced by Disulfide Bond Cleavage in Human Hair after 3.5. Concentration of Thiol Groups (-SH) Produced by Disulfide Bond Cleavage in Human Hair after Treatment Treatment with AMPD Aqueous Solution or Ammonium Hydroxide as an Alkaline Agent with AMPD3.5. Concentration Aqueous Solutionof Thiol Groups or Ammonium (-SH) Produced Hydroxide by Disulfide as an Bond Alkaline Cleavage Agent in Human Hair after TreatmentFigure with 6 shows AMPD a Aqueouscomparison Solution of the or Ammoniumconcentration Hydroxide of thiol asgroups an Alkaline (–SH) Agent produced by cleavage Figure6 shows a comparison of the concentration of thiol groups (–SH) produced by cleavage of of disulfide bonds in human hair immersed in pure water, human hair bleached with H2O2 and Figure 6 shows a comparison of the concentration of thiol groups (–SH) produced by cleavage disulfideAMPD bonds aqueous in human solution, hair and immersed human inhair pure bleached water, with human H2O hair2 and bleached ammonium with hydroxide. H2O2 and The AMPD of disulfide bonds in human hair immersed in pure water, human hair bleached with H2O2 and aqueousconcentration solution, andof thiol human groups hair (–SH) bleached produced with by H 2theO2 cleavageand ammonium of disulfide hydroxide. bonds in AMPD-treated The concentration AMPD aqueous solution, and human hair bleached with H2O2 and ammonium hydroxide. The of thiolhair groups was lower (–SH) than produced the concentration by the cleavage of thiol groups of disulfide (–SH) produced bonds in by AMPD-treated disulfide bond haircleavage was in lower concentration of thiol groups (–SH) produced by the cleavage of disulfide bonds in AMPD-treated ammonium hydroxide-treated hair. thanhair the was concentration lower than the of thiolconcentration groups of (–SH) thiol producedgroups (–SH) by produced disulfide by bond disulfide cleavage bond cleavage in ammonium in hydroxide-treatedammonium hydroxide-treated hair. hair.
Figure 6. The concentration of thiol groups (-SH) produced by cleavage of disulfide bonds in human hair after using 5% ammonium hydroxide or 2% AMPD aqueous solution as an alkaline agent. The FigureFigure 6. The 6. The concentration concentration of thiol thiol groups groups (-SH) (− producSH) produceded by cleavage by cleavage of disulfide of bonds disulfide in human bonds in results are expressed as the mean ± standard deviation of three experiments. ** p < 0.01 vs. ammonium humanhair hair after after using using 5% ammonium 5% ammonium hydroxide hydroxide or 2% AM orPD 2% aqueous AMPD solution aqueous as an solution alkaline agent. as an The alkaline hydroxide. results are expressed as the mean ± standard± deviation of three experiments. ** p < 0.01 vs. ammonium agent. The results are expressed as the mean standard deviation of three experiments. ** p < 0.01 vs. ammoniumhydroxide. hydroxide.
Cosmetics 2018, 5, 39 7 of 10
Cosmetics 2018, 5, x FOR PEER REVIEW 7 of 10 3.6. FieldCosmetics Emission 2018, 5, x Scanning FOR PEER ElectronREVIEW Microscope (FE-SEM) Observations 7 of 10 3.6. Field Emission Scanning Electron Microscope (FE-SEM) Observations Figure3.6. Field7 shows Emission images Scanning of theElectr hairon Microscope surface obtained (FE-SEM) by Observations FE-SEM at ×10,000 magnification. Surface unevennessFigure and 7 the shows number images of of cuticle the hair holes surface decreased obtained in by hair FE-SEM bleached at ×10,000 with magnification. AMPD aqueous Surface solution Figure 7 shows images of the hair surface obtained by FE-SEM at ×10,000 magnification. Surface unevenness and the number of cuticle holes decreased in hair bleached with AMPD aqueous solution comparedunevenness with hairand the bleached number usingof cuticle ammonium holes decreas hydroxide.ed in hair bleached Unevenness with AMPD and curling aqueous of solution the cuticle compared with hair bleached using ammonium hydroxide. Unevenness and curling of the cuticle edgecompared were also with suppressed. hair bleached Figure using8 presents ammonium a graph hydr withoxide. the Unevenness calculated and number curling of cuticleof the cuticle holes per edge were also suppressed. Figure 8 presents a graph with the calculated number of cuticle holes per 100 µmedge2. Thewere number also suppressed. of cuticle Figure holes 8 presents observed a grap in theh with surfaces the calculated of human number hair of was cuticle significantly holes per less 100 μm2. The number of cuticle holes observed in the surfaces of human hair was significantly less after using100 μm AMPD2. The number aqueous of solutioncuticle holes asan observed alkaline in agentthe surfaces than when of human using hair ammonium was significantly hydroxide. less after using AMPD aqueous solution as an alkaline agent than when using ammonium hydroxide. after using AMPD aqueous solution as an alkaline agent than when using ammonium hydroxide.
FigureFigure 7. FE-SEM 7. FE-SEM observations observations of of the the surface surface ofof humanhuman hair hair after after using using ammonium ammonium hydroxide hydroxide or or Figure 7. FE-SEM observations of the surface of human hair after using ammonium hydroxide or AMPDAMPD aqueous aqueous solution solution as as an an alkaline alkaline agent agent (×(×2000)2000).. Top: Top: the the surface surface of ofhuman human hair hair immersed immersed in in AMPD aqueous solution as an alkaline agent (×2000). Top: the surface of human hair immersed in purepure water; water; middle: middle: the the surface surface of of human human hair hair afterafter using 2% 2% AMPD AMPD aqueous aqueous solution solution as an as alkaline an alkaline pure water; middle: the surface of human hair after using 2% AMPD aqueous solution as an alkaline agent;agent; bottom: bottom: the the surface surface of of human human hair hair after after usingusing 5% ammonium ammonium hydroxide hydroxide as an as alkaline an alkaline agent. agent. agent; bottom: the surface of human hair after using 5% ammonium hydroxide as an alkaline agent.
Figure 8. Comparison of the number of cuticle holes in FE-SEM images (×10,000). The results are FigureFigure 8. Comparison 8. Comparison of theof the number number of of cuticle cuticleholes holes inin FE-SEMFE-SEM images images (×10,000). (×10,000). The Theresults results are are expressed as the mean ± standard deviation of three experiments. ** p < 0.01 vs. ammonium expressedexpressed as the as mean the ±meanstandard ± standard deviation deviation of three of experiments.three experiments. ** p < 0.01** p vs.< 0.01 ammonium vs. ammonium hydroxide. hydroxide. hydroxide.
Cosmetics 2018, 5, x FOR PEER REVIEW 8 of 10 Cosmetics 2018, 5, 39 8 of 10 3.7. Oxygen Mapping of Human Hair after Using AMPD Aqueous Solution or Ammonium Hydroxide as an Alkaline3.7. Oxygen Agent Mapping Using EDS of Human Hair after Using AMPD Aqueous Solution or Ammonium Hydroxide as an Alkaline Agent Using EDS The results of EDS-mediated oxygen mapping in human hair after using AMPD aqueous solutionThe or results ammonium of EDS-mediated hydroxide oxygen as an alkaline mapping ag inent human are shown hair afterin Figure using 9. AMPD When aqueoushuman hair solution was immersedor ammonium in pure hydroxide water, oxygen as an alkaline atoms were agent segreg are shownated inaround Figure the9. Whensurface human cuticle hair layer. was The immersed oxygen atomsin pure on water, the surface oxygen of atomsthe hair were bleached segregated using around AMPD theaqueous surface solution cuticle were layer. present The oxygen over the atoms entire on cuticle,the surface whereas of the when hair bleachedammonium using hydroxide AMPD aqueous was used, solution the oxygen were present atoms overwere thelocalized entire cuticle,at the cuticlewhereas edge. when ammonium hydroxide was used, the oxygen atoms were localized at the cuticle edge.
FigureFigure 9. 9. OxygenOxygen mapping mapping by by EDS EDS on on the the surface surface of of hu humanman hair hair following following treatment treatment with with 2% 2% AMPD AMPD aqueousaqueous solution solution or or 5% 5% ammonium ammonium hy hydroxidedroxide as as an an alkaline alkaline agent. agent. Streng Strengthth is is in in order order of of strong, strong, red, red, green,green, blue, blue, black. black.
4. Discussion 4. Discussion Compared with hair that was bleached using ammonium hydroxide as an alkaline agent, hair Compared with hair that was bleached using ammonium hydroxide as an alkaline agent, hair that was bleached using AMPD aqueous solution exhibited improved bleaching properties, that was bleached using AMPD aqueous solution exhibited improved bleaching properties, decreased decreased antioxidant activity, lower protein loss and less cuticle damage. This suggests that a antioxidant activity, lower protein loss and less cuticle damage. This suggests that a bleaching process bleaching process using AMPD aqueous solution suppresses damage to the hair when compared using AMPD aqueous solution suppresses damage to the hair when compared with the conventional with the conventional process for melanin decoloration that uses ammonium hydroxide as an process for melanin decoloration that uses ammonium hydroxide as an alkaline agent. alkaline agent. Concentration measurements of thiol groups (–SH) produced by cleavage at identical pH revealed Concentration measurements of thiol groups (–SH) produced by cleavage at identical pH that lower concentrations were present with the use of AMPD aqueous solution than when ammonium revealed that lower concentrations were present with the use of AMPD aqueous solution than when hydroxide was used. This suggests that disulfide bonds in hair are cleaved when bleached using an ammonium hydroxide was used. This suggests that disulfide bonds in hair are cleaved when alkaline agent. It is thought that cysteine thiol groups contribute to the formation of hair by forming bleached using an alkaline agent. It is thought that cysteine thiol groups contribute to the formation disulfide bonds and crosslinking keratin protein chains. Therefore, the fact that the concentration of hair by forming disulfide bonds and crosslinking keratin protein chains. Therefore, the fact that of thiol groups (–SH) produced by disulfide bond cleavage in hair was lower when using AMPD the concentration of thiol groups (–SH) produced by disulfide bond cleavage in hair was lower when aqueous solution than when using ammonium hydroxide in the bleaching process suggests that using AMPD aqueous solution than when using ammonium hydroxide in the bleaching process the effect on crosslinking between keratin protein chains is lower with AMPD than with ammonium suggests that the effect on crosslinking between keratin protein chains is lower with AMPD than with hydroxide. This theory is supported by the observed maintenance of hair shape, suppression of ammonium hydroxide. This theory is supported by the observed maintenance of hair shape, cuticle hole formation, and lower protein loss. Additionally, the results of oxygen mapping by suppression of cuticle hole formation, and lower protein loss. Additionally, the results of oxygen EDS indicated that oxygen atoms were present on the surface of the entire cuticle of hair bleached mapping by EDS indicated that oxygen atoms were present on the surface of the entire cuticle of hair using AMPD aqueous solution, whereas when ammonium hydroxide was used, oxygen atoms were bleached using AMPD aqueous solution, whereas when ammonium hydroxide was used, oxygen localized at the cuticle edge; therefore, hydrogen peroxide coats the surface of the hair more thoroughly atoms were localized at the cuticle edge; therefore, hydrogen peroxide coats the surface of the hair and remains for longer periods of time when AMPD aqueous solution is used in place of ammonium more thoroughly and remains for longer periods of time when AMPD aqueous solution is used in
Cosmetics 2018, 5, 39 9 of 10 hydroxide in the bleaching process. This is thought to be why the effect of bleaching is stronger using AMPD aqueous solution than when using ammonium hydroxide. AMPD promotes decomposition of desmosome [13] and has a 1,3-propanediol structure, promotes osmosis and has a moisturizing effect on hair. Desmogleins are important proteins in the hair follicle [14]. Adjusting the pH to 8 using aminomethyl propanediol (AMPD) promotes the decomposition of desmogleins by stimulating the activity of exfoliation enzymes, such as kallikrein 5 and 7, which are optimal at this pH [13]. However, AMPD had no effect on the decomposition of desmogleins during bleaching because the pH is 10.75 in a bleaching solution. AMPD is a substituted aliphatic alcohol that functions as a pH adjuster in cosmetic products at concentrations less than 10%. The dermal toxicity data that are presented demonstrate, for example, that mascara with 1.92% AMPD does not cause dermal irritation or allergic contact sensitization, suggesting that the maximum reported concentration of 2% AMPD in mascara would be safe for use [12]. Therefore, AMPD can be expected to have a high affinity for hair, and the bleaching effect of the alkali/hydrogen peroxide can be expected to be persistent. The number of bleaching sessions and the bleach processing times using hydrogen peroxide and AMPD aqueous solutions are topics to be studied in the future.
5. Conclusions The results of this study indicated that in terms of perceived chemical odor, bleaching effect on hair, scanning electron microscope observations of cuticle damage, antioxidant activity of hair and protein loss, AMPD aqueous solution is considered to be more useful than ammonium hydroxide as an alkaline agent.
Author Contributions: K.I. and K.M. designed the study and performed the experiments and data analysis. K.I. and K.M. interpreted the data and drafted the manuscript. K.M. supervised the study and critically revised the manuscript. All authors read and approved the final manuscript. Funding: This research received no external funding. Conflicts of Interest: The authors declare no conflict of interest.
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