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j. Cosmet.
sci., 58, 347-357 (July/August2007)
Hair and amino acids: The interactions and the effects
EIKO OSHIMURA, HIROSHI ABE, and RINA OOTA,
AminoScience
Laboratory,
Afinomoto
Co.,Inc.,Sz/zz/ki-cho
1-1,
Kawasaki210-8681, Japan.
Synopsis
The interactionand the functionof someaminoacidsin hair careapplications
arediscussed.
When amino
acidsareappliedto hairin theformof simpleaqueous
solution,
uptakeof theaminoacidsis mainly
controlled
byionicequilibrium.
Whenaminoacids
wereincorporated
in a hairconditioner,
theresultwas
quitedifferent,
suggesting
theimportance
ofinteraction
between
theamino
acids
andthecationic
surfac-
tants.
Uptake
ofpyrrolidone
carboxylic
acid(PCA),
aderivative
ofglutamic
acid,isenhanced
bycombining
with arginine,anaminowith strongaffinitytowards
hair.
Effectsof someaminoacidson bleached/dyed
hair are described.
A hair conditioner
incorporated
with
alanine
improves
hairsurface
hydrophobicity
ofbleach-damaged
hair.Histidine
andphenylalanine
improve
tensilestrength.
PCAwasprovedto beeffective
to improve
color-retention
of dyedhair.
INTRODUCTION
Proteinisthesecond
majorcomponent
oflivingorganism,
followingwater.All proteins,
includingskinandhair,arevariouscompositions
of aminoacids.
Within the corneocytes,
thereis alsoa complexmixtureof freeaminoacidsandother
low molecularweight,water-soluble
compounds
(NaturalMoisturizingFactoror
NMF)(1), andareknownto contributeto maintenance
of waterbalancein the stratum
corneum.Aminoacids,pyrrolidone
carboxylic
acid(PCA),lactateandurea,all componentsof NMF, arewidelyusedin cosmetic
fieldsandtheirusefulness
iswellestablished.
Unlike in thecaseof theskin,thepresence
andtheroleof naturallyoccurring
freeamino
acidsin hair shaftsarenot knownyet. Althoughfreeaminoacidsareoftendetectedin
hair(2,3),theyaremorelikelyto bea product
ofproteindegradation
caused
by UV or
cosmetic
treatment.But aminoacidsprovidedexternally
areknownto interactwith the
hairto givevarious
cosmetic
effects,
suchasmoisturizing,
strengthening
thehair(4),
and retention of artificial color (5).
In haircareapplications
it hasbeena long-experienced
strategy
to share
theideaofskin
care and utilize materialswhich are establishedin skin care applications.Vitamins,
hydrolyzed
proteins,
vegetable
extracts
aregoodexamples.
Thisstrategy
isoftenproved
to be soefficientthat understanding
of theirbasicinteraction
with hairtendsto be left
behind.In thispaper,interaction
between
hairandvarious
aminoacidsarediscussed
as
well as the benefits of amino acids treatment.
347
348
MATERIALS
JOURNAL OF COSMETIC SCIENCE
AND
METHODS
MATERIALS
Natural hair of Japanese
women, 18 cm in length from tip end, was obtainedfrom
privatesourceandsubjected
to measurement
of physicalproperties.
The hairwastreated
with bleachinglotion for 30 minutesat 33øC,rinsedthoroughlyin runningtap water,
and this processwasrepeated4 times.
After the last bleaching,washingwith 15% active sodium laureth sulfate solution,
extensiverinsingand drying in a conditionedroom (23øC, 40% RH.) followed.
METHODS
UptakeofaminoacidJapanese
hair, treatedwith a wavinglotionof thioglicolicacidand
with a neutralizer of sodium bromate, was immersed in a solution of 11.5 mM amino
acid.After 10 minutesthe concentration
of the aminoacidsolutionwasdeterminedby
HPLC methodusing an artion-exchange
columnand an electrochemical
detector.
Uptakeof PCA. IntensivelybleachedAsian hair swatches,weighing 0.8 g each,were
purchasedfrom Beaulax(Tokyo, Japan).Each swatchwas washedwith a 15 wt%
solutionof sodiumlaurethsulfatefor oneminute,rinsedextensively
with runningtap
water for one minute
and air dried.
A hair swatch was immersed in 6 ml of amino acid or PCA solution for 30 minutes. The
swatchwas rinsedin running tap water for 20 secondsand air dried overnight.For
recoveryof amino acid from the hair, the swatchwas immersedin 15 ml of 10mM
phosphoricacidbuffersolution,pH 3.5. After 30 minutes,10 ml of the buffersolution
was removedfbr quantitativeanalysis.Concentrationof the amino acid or PCA was
determinedby HPLC method.
Hair conditioner
treatment
and hydrophobicity
meas•rement.
Hair conditioner(cationicsurfactant0.6 wt% active,cetyl alcohol3.0 wt%, 0.5 g per tress)wasappliedto wet hair
and distributedmanuallyfor 30 seconds,
then 30 seconds
rinsingin runningtap water
(40øC)followed.The hair tresses
weredried for more than four daysin a conditioned
room (23øC, 40% RH).
A hair fiber wasfixed in a horizontalpositionand 1 pl of aleionizedwater wasmounted
on the point 10 cm from the hair tip end.Twentyseconds
laterthe contactanglewhich
the water drop and the fiber surfaceform was measuredmicroscopically.
Amino acid treatmentand tensilestrengthmeasurement.
A hair swatch was immersedin
100mL of 2 wt% amino acid solution at 35øC for three minutes. The swatch was then
rinsed in 100 ml deionized water at 35øC for one minute, and air dried.
Tensilemeasurements
wereperformedon singlefibersin aleionized
water.Hair fibers,
40 mm in length, were immersedin aleionized
water for at leastone hour beforethe
measurementand then extendedat a rate of 20ram per minute on a tensile tester
KES-G1-SH (Karo Tech) to obtain fbrceneededto extend the fiber by 20%.
Co/or-retention
efj•ct
Test I (Figure 1)
ExtensivelybleachedAsian hair swatches,purchasedfrom Beaulax,were dyed with
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Intensively•,•.
bleached
hair
Color
measurement
•-
Color
measurement
5%PCA
[ Water
l
Semi-permanent Dye
<Dye>
<Wash>
AE*
Figure 1. Experimentaldesignof Test I.
4-amino-3-nitropheol
by immersingin the 0.02 wt% solutionfor 30 minutes.After
removalfrom the dye solution,the swatcheswere air dried.
Treatment with PCA solutionsand color measurement:The pH of 5.0 wt% PCA or
citric acid solutionwasadjustedwith arginine.A hair swatchwasimmersedin 6 ml of
the solution for 30 minutes. Treatment in deionized water was set as control. The swatch
wasrinsedin running tap water for 20 seconds
and air dried overnight.The colorvalue
was measuredby a colorimeter(initial value).
The swatchwasimmersedin 6 ml deionizedwaterfor 30 minutes,air dried overnight,
and the color value was measuredagain (after wash).
-.--q/(Linitial
_ Laft
__ aafte
AE>g
.... h -}-(ainitial
>gr
-}-(binitialbart
.... h)2
RelativebE* wasdetermined
asfollowingin orderto eliminatethe variance
amongeach
experiment:
RelativeAE* = AE*/AEc*ontro•
Test II (Figure 2)
ß Hair dye: Red shade.The dye componentwas the emulsionformula basedon fatty
alcoholsandcontainedfollowingdyeprecursors
anddirectdyes;Toluene-2,5-diamine
sulfate, 2-Methylresorcinol,4-amino-2-hydroxytoluene,
4-Amino-3-nitrophenol,
• '•Post-dye Shampoo
Shampoo
co,or _[Oo,io.er
I,amool!
co,or
Treatment
x 3 times
] Dye
treatment
[
•
Conditioner
x 3 times
measurement;
D
measurement;
B
B
D
D
•
IZ•
Shampoo
x3 times
I
•
D
Shampoo
Conditioner
B
Conditioner
I
x3 times
II
IZ•
.Imeasureme
after6
cycles
oo.,,,o.er
•Shampøø
••E•
Cønditiø
IiSham
t•Cø1
A
B
C
D
A
I•
B
C
D
I•
A
B
C
D
Figure 2. Experimentaldesignof Test II.
I•
I•>
[z•
A
B
C
D
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351
lb
ShampoosUsed in Test II
A
B
C
D
Control
Sodium PCA
Sodium PCA + Arg
Silicone
Na Laureth sulfate (active)
7.56
7.56
7.56
7.56
Cocamidopropylbetaine(active)
1.20
1.20
1.20
1.20
2.00
1.00
--
--
0.40
4.00
q.s
4.00
q.s
Sodium
PCA
Arginine
Amodimethicone, emulsion
--
Pearlizingagent
Preservatives
NaCl
--
--
2.00
4.00
q.s
4.00
q.s
2.00
2.00
2.00
2.00
Citric acid
pH 5.8
pH 5.8
pH 5.8
pH 5.8
Water
Balance
Balance
Balance
Balance
ß'•'10.0
• .=
5.0
0.0
..-.'
..
3
6
9
-5.0
pH value
Figure 3. Arg uptakeat variouspH. Hair: Arg: 5.741 mM, 10 minutesimmersion,40øC.
Arg
Gly
(•
""•o(•
Glu.,.+..%•o. ' .....
O(•
H=N+
--
COOH
...
COO-
I
I
'pH3
pH6
COOI
Hair • :•" ......•" .'•ñ:T:...........
"'....:.... :-(.r
.........
'.....
,.........
'"(!' ' ': ....
•.'r•
........ . .........
-"•• '
. ...........
pH9
Figure 4. Ionic chargeon aminoacidsand hair at variouspH.
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JOURNAL OF COSMETIC SCIENCE
of the solution.It is alsowell known that the chargeson hair alsodependon the pH
(Figure4). The uptakeof aminoacidsfrom the simpleaqueoussolutionsis dominated
by ionic interaction.Arginine, being a basicamino acid, bearscationicchargebelow
pK2 -- 9.04, sohasstrongaffinity for hair at pH overabout4, the isoelectricpoint of
hair (6). Acidic or neutralaminoacidshavingnegativeor neutralnet chargeat pH 3-7
are hardly taken up by hair.
UPTAKE
OF AMINO
ACIDS
FROM
HAIR
CONDITIONERS
When we observethe uptakeof aminoacidfrom a cosmeticformulation,quite different
phenomenaoccursbecause
cosmeticformulationsarecomplexmixture of variouschemicals.The exampleis shownin Figure 5. Although the interactionbetweenglycineor
glutamicacidandhair is veryweakat pH 6, theyaretakenup by hair from conditioner
formulations.This specificdata was obtainedfrom the material balanceof the conditioner solution, so chemical interaction between the amino acids with the cationic
surfactantprobablymakesthe major contribution.
USE OF ARGININE
AS AN
"ANCHOR"
A guanidiniumgroup is known to havequite high affinity for hair protein(7). Figure
6 showsthe amountof argininerecovered
from hair either by water or by acidicbuffer
solution(pH 3.5). The differencewasgreaterat higherpH. This indicatesthe existence
of stronginteractionbetweenacidicgroup on hair and arginine.
This impliespotentialuseof arginineasan "anchor"for the depositionof othercosmetic
materialwith weakeraffinity for hair. One exampleis applicationin combinationwith
PCA. PCA is derivedfrom glutamic acid in the human skin. Saltsof PCA are highly
hygroscopicand thus they are useful as moisturizersand conditionersin cosmetics.
However,beingan acid with small molecularsize,its affinity to hair is relativelylow.
Figure 7 showsthe uptakeof PCA at variouspH. The uptakerisesat pH below4. At
pH over the pKa of PCA and hair, the uptake decreases
becauseof the ionic repulsion
betweenbothcarboxylic
acids.When PCA is appliedto hair asargininesalt,the uptake
was larger than that of sodium salt (Figure 8).
BENEFITS
OF AMINO
ACIDS
FOR
DYED
HAIR
Because
of differentchemicalstructure,aminoacidsarecanprovidea varietyof functions
.•
loo
.o
--- 40
20
/
Uptakefromaqueous
solutions
(pH6)
/
Uptakefromconditioner
formulations
0
•
-20
•
-40
.............
Arg
Gly
Glu
Figure 5. Uptake of amino acids.Amino acid: 11.5 mM, 30 minutesimmersion,25øC.
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COO-
5O
•'
40
o .ff
30
,- •
20
pH 6
....................................................................................
ß By water
.....
-
<l:
10
0
...
3.2
4.3
[] By buffer (pH 3.5)
..
5.3
7.2
pH Value
Figure 6. Recoveryof Arg from hair. Arg treatment:30 minutesimmersion,20 secondsrinse, 25øC.
Recovery:30 minutesimmersmn,25øC.
PCA
25
PCA
O
20
15
..,
pH 6
10
5
0
pH Value
Figure 7. Uptake of PCA: pH dependence.
PCA treatment:5 wt%, 30 minutesimmersion,25øC. Recovery:30 minutes immersion,25øC.
in cosmeticpreparations.Somebeneficialeffectsfound on bleached/dyed
hair are described in this section.
Damagecarebyvarious
aminoacids.Bleachinghair decreases
hydrophobicityof hair fiber
(5). Figure9 showssurfacehydrophobicity
of bleachedhair treatedwith hair conditioners.The averagecontactanglefor naturalhair was100ø andfour-timebleachtreatment
broughtit downto 65ø. By applicationof a simplemodelhairconditionerof monoalkyl
trimmonium chloride,the contactangleincreasedslightly. With 1.5 wt% of L-alanine
addition,the contactangleincreased
significantlyto the similarvalueto that of dialykyl
trimmonium.
Decreasein tensilestrengthof dyed hair fibersis not clearwhen it is measuredin the
dry state, but the effectsof oxidizationare clearwhen measurements
are made in water
(8,9). Figure 10 showstensile strength of bleachedhair measuredin water. Tensile
strengthdecreased
by four-timebleachtreatment,and significantincreasewasobserved
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JOURNAL OF COSMETIC SCIENCE
N=3, mean _+S.D.
3.0
PCA-Arg
PCA-Na
Figure 8. Uptakeof PCA: the effectof counterion. PCA treatment:5 wt%, 30 minutesimmersion,25øC.
Recovery:30 minutes immersion,25øC.
N=20
110
o
---'
100-
o•
90-
<
80-
ß,-,
7'0-
o
o
605O
Bleached
Natural
Bleach
STAC
STAC
+ Ala
I•.
*' p<0.05, **' p<0.01
!•'
Dunnett's
test,control
= STAC
DSDAC
Figure 9. Improvementof surfacehydrophobicity.
50--
N=36
ß
•
20-10--
**' p<0.01
Dunnett's
Bleached
test
0--
Natural
Control
Phe
His
Ala
lie
Arg
Glu
Figure 10. Improvementof tensilestrength.
by applicationof phenylalanineor histidine. In fact, this increaseis attributed to the
increaseof hair fiber diameterwith the tensilestrengthper areabeingunchanged.These
amino acidsare probablydiffusedinto hair fiber and interactwith protein to influence
the structure.
IMPROVEMENT
OF COLOR
RETENTION
BY SODIUM
PCA
Saltsof PCA arehighly hygroscopic.
This propertyis expectedto contributeto retention
of not only water but also other water-solublemoleculesin hair fibers, suchas dye
molecules.
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Test I wasdesignedto examinethis idea.The resultis shownin Figure 11. Basicallythe
influenceof pH is significant,but for all pH conditionsbetter color retention was
observedwith PCA. The differenceof colorretentionat pH 7.2 is impressive.
Figure 12
shows the influence of counter ion on color retention effect: the combination
of PCA and
arginineexhibitedthe best.Taking the "anchor"effectof arginineinto account(Figure
6), the amountof PCA in/on hair seemsto be the key for the colorretentioneffect.
Test II wasdesignedto examinethe color retentioneffect in more practicalcondition.
SodiumPCA wasemployedinsteadof PCA in consideration
of materialavailabilityand
costaspect.Colordevelopmentwassignificantlyimprovedby SodiumPCA or Sodium
PCA/argininecombination(Figure l 3). After 6 or 12 washcyclesYak hair treatedwith
the PCA containingproductsshoweda distinct brighter, more vibrant shade(Figure
14).
CONCLUSION
A variety of methodswere appliedto evaluatethe interactionsand effectsof amino acids
on bleach-or dye-treatedhair. The findingsobtainedin this studyweresummarizedas
follows:
ß When amino acidsare applied to hair as the stateof simple aqueoussolution,uptake
of the aminoacidsis mainly controlledby ionicequilibrium. When aminoacidswere
incorporatedin hair careformulations,interactionbetweenthe aminoacidsand other
ingredients.
ß Uptake of pyrrolidonecarboxylicacid (PCA), a derivativeof glutamic acid, is enhancedby combiningwith arginine,an aminowith strongaffinity towardshair.
ß A hair conditionerincorporatedwith alanineimproveshair surfacehydrophobicityof
bleach-damaged
hair.
ß Histidine and phenylalanineimprove tensilestrength.
ß PCA wasprovedto be effectiveto improvecolor-retentionof dyed hair.
In conclusion,we emphasizethe potential of amino acidsas hair care material. While
morethan twenty specificnaturallyoccurringaminoacidsarefoundin variousproteins,
only a few of them are outlined in this study. Further investigationwill be required.
140
120
100
PCA
Citric
80
60
1.9
2.8
3.2
5.3
7.2
pH Value
Figure 11. Color retentionof semi-permanenthair dye.
acid
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JOURNAL OF COSMETIC SCIENCE
140
LU
120
ß->
100
Na salt
Arg salt
Na salt
Arg salt
n,
80
60
PCA
Citric acid
Figure 12. Color retentionof semi-permanenthair dye: influenceof counterion.
N=3, meanñS.D.
12.0
8.0
4.0
0.0
Control
Sodium
Sodium
PCA
PCA
Silicone
+ Arg
Figure 13. The effectof PCA on colordevelopmentof permanenthair dye.
wash
[]
12 wash
12.0
8.0
4.0
0.0
-4.0
-8.0
Control
Sodium
Sodium
PCA
PCA
Silicone
+ Arg
Figure 14. The effectof PCA on wash-fastness
of permanenthair dye.
REFERENCES
(1) K. Shimizu,Fragra,ceJ.,56, 19-25 (1982).
(2) M. Oku, H. Nishimura, and H. Kanehisa,Dissolutionof proteins from hair. (I) The analysisof
dissolvedprotein from hair,J. Soc.Cosmet.
Chem.
Jp,., 21(3), 198-203 (1987).
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JOURNAL OF COSMETIC SCIENCE
140I
Argsalt NasaIt
120
lOO
8o
60
PCA
Citric acid
Figure 12. Colorretentionof semi-permanent
hair dye:influenceof counterion.
12.0
N=3,
meanñS.D.
8.0
4.0
0.0
Control
Sodium
Sodium
PCA
PCA
Silicone
+ Arg
Figure 13. The effectof PCA on colordevelopment
of permanent
hairdye.
wash
[]
12 wash
12.0
8.0
4.0
0.0
-4.0
-8.0
Control
Sodium
Sodium
PCA
PCA
Silicone
+ Arg
Figure 14. The e•ct of PCAon wash-fasmess
of permanent
hairdye.
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Dissolution
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of
dissolved
proteinfromhair,J. Soc.Cosmet,
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2006 TRI/PRINCETON
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