Use of a chromameter in assessing the efficacy of ... - CiteSeerX

j. Soc.Cosmet. Chem.,41, 369-378 (November/December 1990)

Use of a chromameter in assessinothe efficacyof anti-irritantsand tanninoaccelerators N. MUIZZUDDIN,

K. MARENUS, D. MAES, and

W. P. SMITH, EsteeLauderLaboratories, 125 PinelawnRoad, Melville, NY 11747.

Accepted October 24, 1990.

Synopsis

The chromameter isa toolforprecise andobjective assessment of surface color.Dataoutput,in theformof the L* a* b* colorcoordinatesystemis usedfor differentstudiespertainingto skin color. L* values (darkness/lightness) are usefulin evaluatingand quantifyingthe tanningresponse. The a* values(red/ green)arevaluablefor quantifyingthe degreeof erythema. We havefounda highly significant(p = 0.0002) correlation betweeninstrumental readingsandvisual evaluationof skin colorresponse.

In studiesinvolvingskin tanning,combination of the L*, a*, andb* valueswerestudied.We conclude that L* valuesprovidean objectiveand repeatable measure of skin darkening;however,for a complete pictureof thetanningresponse, AE* couldbecalculated. Forstudies involvingskinirritancy,thea* value is usedto quantifyerythema.The resolution of the datais high enoughto allowfor discrimination and statisticalconfirmationof responses that cannotbe reliablydeterminedby simplevisualassessment.

INTRODUCTION

Erythema andpigmentation aretypicalresponses to ultravioletradiation(1). The detectionof visiblechangein skin coloris affectedby severalunrelatedfactors,suchas viewinggeometry, ambientillumination, colorof unexposed surrounding skin,andthe experience andvisualacuityof theobserver (2). Instrumental objective methods allowforaccurate, repeatable, andunbiased quantification of skin colorand any changetherein.The Minolta Chroma(Reflectance) Meter described byBabulak etal. (1986)(3) isa portable, noninvasive instrument thatquickly andeasilyquantifies surface color.Dataoutputis in variousforms,of whicha* values andL* valuesallowfor simplequantification of surface redness anddarkness/lightness. This monograph describes the objectivemeasurement of the cutaneous response to variousstimuliandcompares thiswith information obtainedfromconventional subjective visual estimations.

369

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JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS

MATERIALS

AND

METHODS

INSTRUMENTATION

Chromameters measure surface colorand surface darkness/lightness to a precisedegree by illuminatingthe sitewith a pulseor floodof light of definedcolor/brightness froma xenonarc lamp. The reflectedlight dividesthree ways, passesthroughfilters, and strikessiliconphotocells.Upon striking the siliconphotocells,light energyis converted into an electricalsignaland sent to a microprocessor whereit is convertedinto coordinates for the chosencolorspace.Data output is in the form of L*, a*, and b* values.L* corresponds to levelsof darkness/lightness betweenblackandwhite. Coordinatea* signifiesthe balancebetweenred/green,and b* betweenyellow/blue.For skin measurements, the q- a* rangeis of particularinterestin measurements of erythema. L* or reflectance valuesare usefulin tanningstudies.

ERYTHEMA

ASSESSMENT:

ANTI-IRRITANCY

STUDIES

A numberof experiments havebeendesignedto studythe anti-irritancyeffectof skin treatmentproducts.The volarforearmof healthyvolunteers(age23-35 yr) is a convenientsitefor suchstudies,althoughfacialskincanbe moresensitive.Studiesweredone with differenttypesof irritants. The most commonlyusedirritant in our studiesis Balsamof Peruin petrolatum.Balsamof Peruis a syrupybalsamfroma tropicalAmerican tree (Myroxylonperurae)growing chiefly in E1 Salvador.It containsfragranceoils

andhasbeenusedin perfumery.However,a majorityof the cosmetic-using population hasbeenreportedto reactto it. The immediatereactionto thiscompoundis in the form of urticaria, which is an irritancyreaction,not involving the systemicantigen-antibodyreactions observed in sensitization reactions (4). Formatofthestudy.Two 3-cm-square areasweredelineatedon the forearms of 14 volunteers. Baseline skin color measurements were noted on both sites as a* values of the chromameter. One site was treated with an anti-irritant. The material was allowed to

absorbfor 20 minutes,and then Balsamof Peruwasappliedon the treatedaswell as the adjacentuntreatedcontrolsite. Degreeof redness(a* values)was recordedat its maximalpoint after 25-45 minutes. Anti-irritant effectswere determinedby comparinga* valuesof the treatedsite with control sites. Baseline redness values of the skin were subtracted from each measurement.

In other studies,anti-irritant materialssuchas indomethacinor hydrocortisone were applied15-20 minutespriorto the irritant. Baseline measurements of bothtreatedand untreatedsiteswereobtainedprior to applicationof the stimulusor anti-irritantmaterial. Visual scoringof erythemawasdeterminedby a panelof trainedjudges.Results wereevaluatedwith a statisticalpackage(Statgraphics) to assess significance.

TANNING

STUDIES

Assessing tanningaccelerators requirespreciseandobjectivequantification of skindark-

ANTI-IRRITANTS

AND TANNING

ACCELERATORS

371

eningin response to UV irradiation.L* valuesareusedfor measurement of skinlightness.Fora complete pictureof thetanningresponse, AE* canbecalculated asfollows:

A E* = X/(AL*)2 q- (A a*)2 q- (A b*)2 AE* thenrepresents the linearcombination of changes in bothskinreflectance aswell as color.

In the followingstudiesskin tanningwas assessed visuallyas well as with L* values measured by the chromameter. The MED for eachpanelistwasdeterminedto obtain the optimumUV dosefor the experiment.Tanningproductswereappliedon the skin beforeor afterexposure to the solarsimulator,at the appropriate UV doselevels.

Twenty-four-hour erythema wasmeasured by a* values,andafter48-72 hourstanning wasdeterminedby the changein L* valuesascompared with the controlsiteexposed to the samedoseof UV irradiationbut not treatedwith tanningaccelerator. Visual evaluation of tanningwasconducted by a panelof trainedjudgesona 1-4 standardized scale. The resultswere evaluatedwith a statisticalpackage(Statgraphics)to assess significance.

RESULTS ERYTHEMA

ASSESSMENT

Correlation of instrumental and visualassessment. In orderto determineif the resultsobtained from the chromametermeasurements were in agreementwith thoseobtained from visual assessment,we determined the correlationcoefficientfor results obtained

via both measuringtechniques (TableI). After subtractingthe baselineskin measurements, the product-treatedsite valueswere subtractedfrom the a* value of the untreatedsite to obtain Aa* value (Table II).

Visual scoringof skin erythema,asgrade 1 to 4, basedon a standardized scale,was

doneby a panelof trainedobservers andcompared with the Aa* valuesobtained with the chromameter(Figure 1). The visualgrading of skin erythemais generallyconsideredthe differencebetweenbaselineskin colorand increase in redness asobserved by the eye. We founda significantcorrelation(r = 0.6785, p < 0.001) betweenvalues obtainedon increase of redness andvisualgradingof skin erythema.

Anti-irritancystudies. The efficacyof an anti-irritantchallengedby eithera chemicalor physicalstimuluswas determinedin terms of inhibition of erythema(a* value) and comparedwith the skin area treated with irritant alone. Figure 2 showstwo sites treated with

the chemical irritant

Balsam of Peru. Site B is a control that was not

Table

I

CorrelationBetweenVisualScoringandChromameter Readingsfor the Measurement of Skin Erythema Chromameter

n = 14

Visual

Correlation

gradingA a*

grading

coefficient r

3.29

1.!

0.6785 (p < 0.00!)

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JOURNAL OF THE SOCIETYOF COSMETICCHEMISTS Table

II

Anti-Irritancy Effectof Product Baseline

Treated

Control

skin color

site A

site B

9.29

13.55

0.64

4.9

a* Values

8.65

A a*

% Decrease in erythema

86.94%

pretreatedwith the prospectiveanti-irritant. Site A, on the other hand, was treated

with theanti-irritantmaterialat a doseof 2 mg/cm2, 20 minutespriorto application of the irritant. As illustratedin Table II, the efficacyof the anti-irritant in this caseis quite clear.Chromameter measurements of bothsiteswereobtained(1) prior to applicationof the irritant (baseline) and(2) afterdevelopment of maximalerythema.Several measurements weretakenin orderto insurereadingthe reactionat its maximalpoint, whichoccursabout30-40 minutesafterapplication of the irritant. In addition,at each time point five to six replicatesof eachmeasurement wereobtained.For the mostpart, the varianceof the replicatesis about0.11; however,if the skin is blotchy,the variance increases slightly (0.18). Therefore,eight to ten replicateswereobtainedfor eachmeasurement.

As illustratedin TableII, it ispossible to quantifytheefficacy of a prospective anti-irritant ingredientby evaluatingthe differencein erythemaafter subtractingbaseline values. MeBBuPemen•

o•

Erythema

with

CH•IOMAMETEI• 4O

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vJ. su•

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1

Figure 1. Erythema:Correlationbetweenvisualmeasurements and chromametera* values.

I

ANTI-IRRITANTS

control

AND TANNING

ACCELERATORS

373

test

Figure 2. Anti-irritancyassessment.

TANNING

In studiesto assess changesin skin color due to tanning, the chromameteris also valuable(Figure3). "Pre-tan"productsusuallyseekto reducethe amountof UV requiredto achieveskindarkening.Other productsseekto extendthe time of skin darkening from a singleUV stimulus. In thesestudiesthe subjectswere treatedwith a tanning productand then exposedto

varyingdoses of UV irradiation(range100-210 mJ/cm2) (TableIII). The controlsite wastreatedwith similar UV doseswithout the product.

After 48-72 hours,skin darkness values(L*) on the product-treated sitesweremeasuredwith thechromameter andsubtracted frombaseline L* values.Figure4 illustrates the resultsof onesuchstudy. Here it is clearthat therewasa doseresponse relationship

betweenskindarkness andincreasing UV-B exposure. In additionto L* values,the a* valuesfor redness,aswell asb* valuesfor yellowcoloration,increased with increasing tanningresponse. A combination of the threecolorvalueswerecalculated asAE*.

Althoughreflectance (L*) valuesindicateskinskindarkness/lightness, a combination of the colorvaluesappears to bestdepictthe tanningresponse asseenin Figures4 and 5. Correlations betweenUV-B exposure andAE* werehighlysignificant(r = 0.9922, p < 0.001).

The degreeof tanningwasalsoassessed by a panelof trainedobservers. Scoringwas basedon a four-pointsystem.Therewasa significantcorrelation(r = 0.895%, p < 0.001) betweenvisualgradingandquantificationof skin darkeningwith the chromameter (Table IV).

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JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS

I•eaeurement

of

Tanning

w•tla

lo

I I I

I I I I I

I I I I

I I

[ I I I I I

I

I

Figure 3. Tanning: Correlationbetweenvisualmeasurements and chromameterL* values.

Relationship between redness and •rknessvalues.We haveobserveda changein the L* valuewith increasein erythema,and in turn the a* valuesalsoincreasewith an increase in tanning. Investigationof the relationshipbetweenthe two valuesshowedthat an increase in redness (a* values)is independent of darkness valuesin the caseof erythema (Table V).

Increasein darkness (L* values)in the caseof skin tanning,however,correlates with an increase in redness due to an increase in reflectance of melanin between 550-600

nm

(5). For tanningstudies,skindarkness measurements (L* values)areobtained48-72 Table

III

UV-B and Skin Tanning Measurements UV-B

dose

mJ/cm 2

/x L*

210 195 170

7.82 7.06 5.71

4.00 3.17 0.17

8.76 8.57 6.17

12.4 11.55 8.41

130 106

4.29 3.33

0.08 0.01

3.95 2.66

5.83 4.26

0.9965

0.8623

r

p