hair greasiness

8/11/2019 Hair Greasiness

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J. Soc. Cosmet.Chem.27, 3-14 (1976) 1976 Societyof CosmeticChemists f Great Britain

Sensory erception nd

of hair greasiness

evaluation

G. C. DOBINSON* and P. J. PETTERt

Presentedat the Symposiumon 'A Sensory Approach to

Cosmetic Science' organized by the Society of Cosmetic

Chemists f Great Britain at Manchester n 7-9th April 1975

Synopsis--The eneralprinciples f SENSORY EVALUATION are briefly discussed, ith

particular eferenceo the assessmentf HAIR propertiesn the laboratory.Two procedures

are described. he 'meter method' in which assessorslace sampleson a scale, s rapid, simple

to analyse, nd mostuseful or self-containedxperiments.he 'rankingmethod' n which two

or moresamples re compared t a time, is slowerbut more sensitive nd better suited o

intercomparisonof experiments singa common standard.

The usefulness f sensory esting o the cosmetic hemist s illustratedby a study of hair

greasiness,esignedo relatesensoryssessmentf greasinesso the rheologicalharacteristics

of the grease. ilms of oils, greases nd waxes,coveringa wide rangeof CONSISTENCY, were

deposited nto hair switchesor tactileand visualassessment.or the oils, both tactile and

visualgreasinesshowed positiveinearcorrelationwith the logarithmof viscosity,measured

by cone-and-plateiscometer. or the greases nd waxes, actile greasiness as negatively

correlatedwith yield value, measured y cone penetrometer, hile visualgreasinesshoweda

maximum in the centre of the consistency ange.

INTRODUCTION

Sensoryestings well establishedn cosmetic cience s a meansof

assessinglavours, ragrances, tc. Its application or the evaluationof

physical ropertiess lesswellknown,particularlyn the aboratorywhere

instrumentalmethods end to predominate.n fact, it may be that the

average osmetic hemistwould tend to regardsensorymethodsas in-

* Presentaddress:Central Electricity GeneratingBoard, Sudbury House, London, E.C.1.

? UnileverResearch,sleworthLaboratory,455 London Rd, Isleworth,Middlesex.


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4 JOURNALOF THE SOCIETYOF COSMETICCHEMISTS

herently ess eliable han instrumentalmethodsand only to be usedwhere

there is no obvious nstrumentalapproach. t is possible,however, or a

panel of assessorso functionas a usefulevaluation ool providedcertain

conditionsare observed.Such a panel can be used not only for assessing

complexpropertiessuch as 'body' or 'condition' of hair but also as an

alternative o an instrumentalmeasurement,or example,of combability.

In this paper we shall briefly review someexperimental pproacheso

sensory estingof hair propertiesand illustratewith someresultsobtained

from a study of hair greasiness.t is generallyconvenient,although ob-

viously essrealistic, o carry out such evaluationsunder laboratory con-

ditions usinghair switches ut, in principle, he methodscan be applied

in vivo.

GENERAL PRINCIPLES OF SENSORY EVALUATION

It is not intended o surveysensory valuation ully: this topic hasbeen

well coveredby Harper (1).

In order to usehuman beingssuccessfullys assessorsor evaluationof

someproperty,certainprecautions houldbe taken: the test environment

(light, temperature,humidity, etc.) should be kept constant;distractions

shouldbe eliminated;assessorsn the samepanel shouldbe given dentical

instructions.The number of assessorsequireddependson several actors

amongstwhich are the requiredaccuracyof the results, he numberof test

items, the magnitudes f property differences etween tems and the skill

of the udges.As assessorsain experience nd confidence, heir judgments

usually become more consistent.No assessor hould observeeither the

results of another's assessment or how that assessment was obtained.

An assessor an be requested ither to indicate the magnitudeof some

propertyof a testsampleor to rank two or more samplesor that property.

When using he former of thesealternatives,t is frequentlyconvenient

to place each sampleon what has been designated s a meter for the test

property.This meter,which may be, for example,a lengthof bench op or

a horizontal rod, has no subdivisions nd the assessor ecides or himself

what the range covers.How differentassessors ight use the meter is in-

dicated in Fig. 1. Eight assessors ave independentlyplaced four test

samples long a designatedmeter n order to indicatemagnitudes f some

defined roperty.This example emonstrateshat assessorsre usingdiffer-

ent mental scales e.g. assessors and 7) and of coursedo not necessarily

agreeon the rank order. All assessments,owever,can be put on the same


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SENSORY PERCEPTION AND EVALUATION OF HAIR GREASINESS 5

Assessor I

Assessor

Assessor

Assessor 4

Assessor 5

Assessor 6

Assessor 7

Assessor 8

D C MB

c D

O - C M B

M A

O C M B A

12'

I I

D BM C A

D C M B A

% C M B A

Higher values >

Average O C M B A

o-

Figure I. The meter method.

scaleby standardizing o that all assessorsave the samemean (M) and

standarddeviation c0. When this is done, all assessmentsan be averaged

together o give an overall assessmentn terms of averagescalevalues.

This is shown n Fig. 1.

The overallrank order obtained s generally ound to be reproducible

betweendifferentpanelsof assessors,ut becausendividualsuse different

mental scalesboth the averagescale values and the differences etween

them are characteristic f the particularpanel used.Therefore t is difficult

to compare the results of one test with another, even when one common

standard s used. For a self-contained xperiment,however, his method

does have the advantagesof speedand simplicity of analysisover the

ranking method describedbelow.

An alternativemethod of investigating roperty magnitudes sesdata

in the form of rankings.At leasttwo of the test samples re considered

togetherand the assessorndicates he order of the samples.He will generally

go on to rank further setsof test samples, p to a maximum of about ten

sets n order to avoid panellist atigue. It is possible o constructexperi-

mental designswhich are balancedwith respect o suchvariablesas number

of replicates nd positionof samples efore he assessor.he design hould

allow comparisonso be made of samples oth of the same ype and of

different ypes,so that the variancewithin each type can be compared o

the variancebetween ypes.From the ranking data it is possibleo generate


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6 JOURNALOF THE SOCIETYOF COSMETIC HEMISTS

Presentation Ranking Number

A B C A B C 2

A C B 2

B A C 2

B C A I

C A B I

C B A 0

B A D A B D 3

A D B 2

B A D 2

B D A I

D A 8 0

D B A 0

C D A A c D 3

A D C 2

C D A 2

C A D I

D A C 0

D C A 0

D C B B C O 2

B D C I

C D B I

C B D 2

D B C I

D C B I

I

32

Scale values

4,/( A ): 0.63l

M(B) = 0-072

M( C ) = -0-067

M( D ) = -0.636

Figure2. The ranking method.

scale alues.Our methoduses generalization y Levitt (2) of the Bradley-

Terry model (3) which s basedon the assumptionhat a pairedcomparison

is probabilistic, .e. for any pair the comparisonwill not always favour

the same tem. An exampleof the results hat could be obtainedwith this

method is given in Fig. 2, where four samplesare examinedby eight

assessors,achconsideringour triads. For the purposes f illustration he

example s simple; t is quite ikely that an experimenter ould wish to use,

for example,more assessorsr more assessmentser judge.

There are severaladvantages f the ranking approachover the meter

method, he most important one for the experimenter eing hat the scale

valuesobtained rom one test can be compareddirectly with the resultsof

another if there is some common standard n each test, since the model

givesadditivescale alues.Thereare, however,otheradvantages. ssessors,

for example, usually find identifying rank order easier than indicating

magnitudesespeciallywhere differences re small. There may also be

specific easons or preferring he ranking method as, for example, n the

greasinessxperiment o be describedater, where t was essential o avoid

contaminationbetweensamples.


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APPLICATION OF SENSORY TESTING TO HAIR

In applyingsensoryesting o the measurementf hair properties,he

hair switches sedwill dependon the propertiesunder study. n this work

the test sampleswere straight switches repared rom European hair so

that eachswitchwas 24 cm long by 2 cm wide and contained .4 g cm4 of

hair along ts ength.Additionalprecautions re necessaryn order o ensure

that error is not introduced nto the experimentalwork becauseof initial

switchdifferences. he hair to be usedshouldbe carefullyrandomizedand

cleaned o removeany surface eposits.When the switches avebeenpre-

pared they shouldbe storedcarefully o avoid contamination.

When assessors examine such hair switches--either to rank or estimate

propertymagnitudes--it s usuallyconvenient o hang the switchesrom

a horizontalbar by meansof hooksattached o their clamped-root nds.

APPLICATION IN A STUDY OF HAIR GREASINESS

The examplewe have chosen o illustrate sensory valuationof hair is

taken rom a studyof the problemof hair greasiness.he factorscontrolling

hair greasinessnd ts perception re complex, ut must nclude he physical

properties f the greasy ilm of lipid materialon the hair surface, nd, more

specifically,ts rheological haracteristics.he experimentso be described

wereaimedat establishingowpeople's ensory ssessmentf hair greasiness

correlateswith the rheologicalparametersof the grease.Tactile and visual

judgmentswere studiedseparately, inceboth modes were believed to be

important in the self-assessmentf greasiness.While the relevance of

rheology o the feel of greasyhair is clear, a possibleconnectionwith

appearances perhaps essobvious.However,the most important visual

clue to the presence f greaseon hair, apart from changesn gloss, s the

so-calledrats-tail'effect,when he hairs end to adhere ogether n bundles,

and it was this aspectwhich was studied.

The general lan of the work was o take a numberof materials overing

a wide rangeof consistency,rom thin mobile oils throughgreaseso solid

waxes, o characterize hem rheologically nd to assesshem by sensory

testingon hair switches or their greasiness, ither tactile or visual. The 11

materialsselected re shown n Table . The seriesbeganwith four silicone

oils of increasing iscosity,anging rom a nominal 100 centistokes'p to

'one million centistokes'. Next came semi-solid materials which would

normally be thought of as 'greasy': anolin, petroleum elly and a high


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Table I. Materials selected or greasiness xperiments

Code Material

Increasing consistency

SIL 1 ]

SIL2 --Poly(dimethylsiloxane)luids

IL 3

SIL4

LAN Lanolin

PJ Petroleum elly

PEG Poly(ethyleneglycol)

LIP}

IP II --Synthetic mixtures of lipid materials

LIP III

WAX Paraffin wax

molecularweight poly(ethylene lycol). Mixtures of lipid materials pre-

dominantlyoleic and stearicacids and their glycerolesters)were used o

span he gap between he greases nd the relativelyhard paraffinwax.

These materials were applied to hair switchesby spraying 1o w/w

solutionsn etherfrom pressurized erosolpacks.Each switchwas sprayed

until the depositequalled1 /o of the weight of the hair (this being ypical

of the grease evels ound on hair in vivo)and finally the hair was combed

through o promoteuniformdistribution. Preliminaryexperiments howed

that this combingstep did not remove a significant mount of material

from the switch.) Materials were compared hree at a time in a seriesof

sensory ests, inked togetherby includingeach ime one material common

to the previousgroup. In this way, the completebody of data could be

analysed ogether o give an overall picture, placing all 11 materialson a

scaleof relative greasiness.

The sensory ssessmentsere carriedout according o the general ank-

ing procedure lreadydescribed. actileandvisualassessmentserecarried

out separately.n the tactile test, switcheswere presentedor ranking n

pairs,hangingbehinda screen o that the panellists ould eel but not see

them (Fig. 3). In order to avoid transfer of material betweenswitches,

panellistswere asked o feel one switch n each hand, and to wash heir

hands betweeneach pair. Six switcheswere used or each est, made up of

duplicatesor eachof the threematerialsbeingcompared. welvepanellists

eachassessedix pairs, n the courseof which everyswitchwas felt twice,

once n the left hand and once n the right, in order to take accountof any

bias.

In the visual est, panellists ould see he switches ut were not allowed


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JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS

:' /

Figure 3. Tactile assessment f greasiness.

Facing page 8


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l0 JOURNAL F THESOCIETYF COSMETICHEMISTS

conepenetrometerasusedo measureheyieldvalue i.e.theminimum

stresselowwhichhematerialeaseso flow).Bothof these restandard

techniqueso be oundn mosthealogicalextbookse.g. herman4)),

andneedbedescribednlybrieflyhere.

Thecone-and-plateiscometerFig. ) consistsssentiallyfa slightly

conicaliscotating ithtsapexust ouchingflatstationarylate. he

fluid amplescontainedn he ap etweenonend late,ndhe orque,

Q Torque

I G

I

Speed

D I

'Cone

Sample..

i Plate

I

I

I

Torque, G

Dynamiciscosity,'/ Constant(Speedf otation,

Figure5. Ferranti cone-and-plateiscometer.

G,on hecone anbemeasuredt any otationalpeed,. It canbeshown

that he hearatesconstanthroughouthe amplendhat hedynamic

viscosity,, is givenby'

KG

where is a constantependingnlyonthegeometryf thecone. he

plotof G versus wasa straightine or the hinnestiliconeil, but

becamencreasinglyurvedor the emaininghree nd n these aseshe

'lowshear'iscosityas alculatedrom he nitial lope.

Thecone enetrometerFig.6) is a standardnstrumentor characteriz-

ing atsandgreases,nd hemethod sedo obtain ieldvaluesrom

penetrationeasurementsas hatdescribedy Haighton5). In this

instrument,cone, f weightW,penetratesnder ravityhe latsurface

of thesamplen a cylindricalup.Aspenetrationroceeds,hesheartress


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SENSORY PERCEPTION AND EVALUATION OF HAIR GREASINESS ll

Cone weight,

Penetrotion

log

14/

lope:

Yield value =Consfont x

Cone weight, 14/

(Penetrotion,

igure6. Cone penctromcter.

log p

decreases ntil it reachesa value ust balancedby the rheologicalstability

of the sample, nd the coneceaseso move.From this equilibrium enetra-

tion, p, the yield valuemay be calculated s

yield value -

kW

where k is a constantdependingon the cone angle and is tabulated by

Haighton. The value of n is approximately , and may be found by loading

the cone o variousweights,plotting og W against og p and determining

the slopeof the line. In this work, n was ound to have an average alue of

1.79.

The resultsof these wo rheologicalmeasurements re given n Table I.

The yield value quoted or paraffinwax is an approximate igure, since he

penetrometerwas not really suitable or such a hard material, and the

penetrationwas too small to measureaccurately. t was not practicable o

carry out thesemeasurements t a temperatureother than 25C,although

it is recognized hat this is not identical o the temperatureof the materials

duringsensory ssessment:he visualassessmentsere carriedout at room

temperature 22C) while in the tactile assessmentshe films must have

beenat some emperature etween oom and body temperatures.

Let us now consideragain the sensory est results n relation to these

values.First, for the siliconeoils (Fig. 7), plotsof sensory reasinessgainst


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o

Tactile

'0"0'-- -. 0 corr.oefff.= .98

Visual

I I0 10 I0" I0

Yield value kN m2)

Figure 8. Sensoryand instrumental measurements or greases nd waxes.

important n determining he sensory ssessmentf the consistencyf skin

creams Suzukiand Watanabe 6)) and the easeof application o the skin

(Barry and Grace (7)). The relationship or visual greasinesss obviously

more complex han that for tactile greasiness. he increasewith increasing

yield value over the lower half of the rangeprobably eflects he increasing

tendencyof the hairs to adhere ogether o form 'rats-tails',with the ease

of separationof the hairs inversely elated to the yield value. It seems

reasonable, owever, hat eventually he curve will turn down again n the

hard, waxy region, as indicatedby our result or paraffin wax.

Although more work is required before the physicalbasisof the per-

ception of hair greasiness an be fully understood, hese resultssuffice o

demonstratehat it is possible o obtain quantitativemeasurementsf hair

greasinessy meansof sensory ssessment. oreover, our work on hair

switches ould, in principle,be extended o assessmentn vivo,comparing

the greasiness f real heads, although so far we have made only a few

preliminary experimentsn this direction. Finally, we would emphasize

again hat greasinesss ust one exampleof a propertywhichcan be evalu-

ated by sensory esting. We have successfullypplied the technique o a

wide range of hair properties, ncluding, or example,combability, gloss,

softness nd 'fly-away',and the sensory pproach s particularlyuseful or

propertieswhichhave no obviousphysicalcorrelate hat can be measured

instrumentally.


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ACKNOWLEDGMENT

We should ike to thank Mr N.J. McNeice who carried out the experi-

mental work.

(Received: oth February1975)

REFERENCES

(1) Harper, R. Human sensesn action 1972) (Churchill Livingstone,Edinburgh).

(2) Levitt, D. J. J. ScFood Agr. 24 739 (1973).

(3) Bradley, R. A. and Terry, M. E. Biometrika 39 324 (1952).

(4) Sherman, P. Industrial rheology 1970) (Academic Press,London).

(5) Haighton, A. J. J. Am. Oil Chemists'Soc. 36 334 (1959).

(6) Suzuki, K. and Watanabe, T. Amer. Perfum. Cosmet.85 115 (September,1970)

(7) Barry, B. W. and Grace, A. J. J. Pharm. Sci. 60 1198 (1971).

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