j. Soc.Cosmet.
Chem.,39, 107-119 (March/April1988)
A new in vitro methodfor transepidermalwater loss:A
possiblemethodfor moisturizer
evaluation
L. M. LIEB, R. A. NASH, J. R. MATIAS, and
N. ORENTREICH, St.John'sUniversity,
Jamaica,NY 11439
(L.M.L., R.A.N.) and Orentreich
Foundation
for theAdvancement
of
Science,
Inc., 910 Fifth Ave., New York,NY 10021 (J.R.M., N.O.)
Received
October19, 1987
Synopsis
Transepidermal
waterloss(TEWL) throughthe ventralskinof the hamsterearwasdeterminedusinga
modifiedflow-throughdiffusionapparatus.Tritium-labeledwater wasallowedto permeatethroughthe
dermal/epidermal
layers.Water vaporwascollected
in a closedsystemby adsorption
ontosolidanhydrous
calciumchloridein a separately
attachedreceiver.The desiccant
wasremoved,dissolved
in water,and the
radioactivity
determinedby liquid scintillationcounting.The rateof TEWL wasdetermined
for various
durations
ofexposure
to thedesiccated
environment,
in thetemperature
rangebetween
5 and40øC.TEWL
rate reacheda maximumonehour after exposure,and then decreased
to a steadystatewith time. TEWL
increasedexponentiallywith increasingtemperaturein accordance
with the Arrheniusrelationship.An
activation
energy
valueof 13Kcal/mole
wasobtained.
At incubator
temperature
of22øC,therateofTEWL
wasfoundto be 152 _+ 14 p,g/cm2/hr,
whichagreeswith previously
reportedvaluesobtainedby in vivo
methodsof testing.The presenttechniqueis proposed
asa rapidin vitromethodfor measuring
TEWL and
asa possible
pretestfor assessing
efficacy
of potentialskin-moisturizing
agents.Fouragentswerestudied
for their effecton waterpermeability.The agentstestedweremineraloil, castoroil, sesame
oil, and 25%
glycerinin water.Skinmembranes
treatedwith occlusive
agentssuchasmineraloil, castoroil, andsesame
oil showeda marked decreasein the TEWL rate, while thosemembranestreatedwith the humectant, 25%
glycerinin water,showed
a markedincrease
in theTEWL rate.Similarresultsusingthesesameagentshave
beenreportedpreviously.
INTRODUCTION
Blank showedthat properhydrationof the stratumcorneumis a primaryfactorin
maintainingskinsoftness
andflexibility(1,2). Otherconstituents
of skin, suchasproteinsand lipids, play a minorrole by influencingthe water-binding
capacityof the
stratumcorneum.Appearance
and barrierfunctionof the skin is affected,if it is not
optimallyhydrated(3). Thiseffectis exhibitedin low relativehumidityenvironments,
wherethe skin becomes
dry, flaky, and/orchapped.When skinhydrationincreases
at
higherrelativehumidity, the watercontentand the permeabilityof skin increases
(1,2,4-10). It is considered
supple,flexible,pliable,and lesslikely to chap,fissure,
and crack (1,2, 11- 14).
Somecosmeticchemistsregardmoisturizationas any meansto increasewater content
and maintainthis level overa periodof time (15). "A moisturizer,"as definedby
Kligman(16) "is a topicallyappliedsubstance
or productthatovercomes
thesignsand
107
108
JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS
symptomsof dry skin." In simple terms, the alleviationof the dry skin state after
"moisturizers"
are appliedexternallymay be partly due to the increased
hydrationor
water contentof the skin (1). One of the methodsusedto assess
the hydratedstateof
the skin is to measurethe percentdecrease
of transepidermal
waterloss(TEWL) on skin
treatedwith a moisturizerversusuntreatedskin. TEWL is a passivediffusionalprocess
wherewatervapordiffusesfrom highly hydrateddermal layersvia the stratumcorneum
to the exteriorsurfacewhere it evaporates
freely.
Levequeet al. (17) recentlymadein vivoTEWL measurements
(Servomed
© evaporimetertechnique
of Nilson)of dry skinpatientsandcompared
thismethodto the regressionmethodof Kligman (16). A statisticallysignificanttrendwasobserved
with TEWL
and dry skin, althoughthe two did not correlateclosely.It is notedthat an increasein
TEWL (from normallevels)during a dry skin statesuggests
a disturbancein the horny
layerstructure.However,during this statethere'salsoa tendencyof dry skin to form a
thickerhornylayer, counteractingthis effect(17). This methodof measuringmoisturizing efficacyvia TEWL ratedecrease
hasits limitationsandis a subjectof controversy.
Other methodsthat havebeenusedto hydratethe skin include(18): 1. applyingexternalwaterdirectly to the stratumcorneum,and 2. increasingthe rate of diffusionof
water from the lower epidermallayersthroughthe stratumcorneum.
Accordingto Wu (19), transepidermal
water lossis describedby the term calledflux
and is expressed
by Fick'ssecondlaw:
J = D(C) dC/dX
whereJ equalsflux, in Ftg/cm2/hr,C equalswaterconcentration
in the stratumcorneum, •tg/cm3, X equalsthe thickness
of skinmembrane,cm, andD(C) equalsdiffusivityof waterin the stratumcorneum,cm2/hr.D(C) is a constantdeveloped
by Wu
(19) to describethe diffusivityof waterand its relationto the barrierpropertiesof the
membrane
FACTORS
utilized.
AFFECTING
TEWL
The environmentaltemperature,relativehumidity, and skin sourcemust be controlled
during experimentation
in orderto determineTEWL. This requirementis evidentby
the large variation in TEWL values,reportedpreviously:100-1500 Ftg/cm2/hr
(1,4,6,9,20-26).
In vivostudiesby Grice et al. (20,21) and in vitro experimentsby Matias (22) have
shownthat TEWL will increaseexponentiallywith increasingtemperature.Reportsof
the effect of environmentalrelative humidity on TEWL, however, are in conflict
(23-26). Using differentexperimental
methods,Goodmanand Wolf (23), Spruitand
Malten (24), and Bettleyand Grice(25) showedthat the waterlossthroughskin decreases
asrelativehumidity increases.
Morerecentcontrolledin vivostudiesby Grice(26)
revealeda maximumTEWL ratebetween50% and 75% relativehumidity(RH).
In vitro measurements
with fetal hog peridermby Wu (19) have confirmedGrice's
findings(26). The integrity and sourceof skin usedin in vitrostudiesare alsocritical
factors.It has been reportedthat diseased
and damagedskin have increased
TEWL
(27-28). Dupuis (29) reported a TEWL value from foreheadskin almost twice that
from skin at other anatomic sites.
METHOD FOR TRANSEPIDERMAL WATER LOSS
109
Application of topical vehiclescan either increaseor decreasethe hydration of the
stratum corneumdependingon how the vehiclealters water activity in the barrier.
Oily, occlusivematerials,suchaspetrolatum,mineral oil, lanolin, and isopropylmyristate,significantlydecrease
the rate of waterlossfrom the skin. Theseagentscanbe
considered
moisturizingagentssincethey are able to increase
skin hydration.Humectants,agentsthat act to bind waterto skin, suchasglycerinandpropyleneglycol,can
increaseskin moistureby interactingwith the atmosphericmoisturein conditionsof
moderateto high humidity. When the relativehumidity of air decreases,
humectants
on the skin, however,will extractmoisturefrom the deeperlayers.Riegerand Deem
haveshownthat humectants
increase
the in vitroTEWL at conditionsof low humidity
(30). Humectantsalone,therefore,only functionasa moisturizerin properatmospheric
conditions.It is conceivable
that the moisturizingemulsionscanstill decrease
TEWL,
at various humidities, even with a humectantpresentin the formula. Decreasing
TEWL presumably
increases
the poolof wateravailableto hydratethe skin. It is possibleto determinethe influenceof TEWL on moisturizereffectiveness
by comparinga
TEWL
value on untreated skin to that value obtained from moisturizer- or occlusive
agent-treatedskin (30).
In vitromethodsfor TEWL measurement
canbe utilized to pre-evaluatethe potential
efficacyof moisturizers
in humanskin. Presentin vitromethods(1,2,4,7,8, 19,30- 33)
are time-consumingto usefor this purpose.Another limitation is that water lossfrom
the skin canconflictwith waterlossfrom the moisturizer.The objectiveof the present
researchwasto developa simpleand accuratemethodthat permitsrapid evaluationof
TEWL of potential moisturizersby a quantitative measurementof moisture loss
throughan animalskin membrane.This methodusesa tritiated-watertracertechnique
whichcaneliminateerroneous
TEWL valuesthat may resultfrom the waterevaporation
from a moisturizer.
EXPERIMENTAL
APPARATUS
PROCEDURE
DESIGN
A modificationof a flow-throughdiffusioncell originallydesignedby Bronaugh(34)
wasutilized. The membranewasfull-thickness,cartilage-stripped
skin taken from the
ventral ear of the male Syriangoldenhamster(Harlan-SpragueDawley, Indianapolis,
IN) asdescribed
by Matias(35). Tritiated water(HTO) permeatedthroughthe membraneinto the receptorcompartmentof the diffusioncell. Flux (TEWL) wasdetermined,via scintillationcounting,by the measurement
of HTO that adsorbed
on anhydrouscalciumchloridein the receptorcell. A TEWL rate-vs-timestudywasconducted
to determinethe time to steadystateor equilibriumconditions
at 32øC.The prepared
cellswere then exposedto temperatureincrementswithin the rangebetween5 and
37øC,andthenTEWL measured
at steadystate.A plot of the logarithmof TEWL vs
the reciprocalof absolutetemperaturewas usedto determinethe energyof activation
(by slopeanalysis)
in accordance
with the Arrheniusrelationship.
An evaluationof TEWL was conductedfor skin treated with three occlusiveagents:
mineraloil, castoroil, andsesameoil, andskin treatedwith a humectant(25% glycerin
110
JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS
in water)by addingthe 10 IxL of the agentontothe exposed
skin area(0.32 cm2) and
conductinga TEWL rate-vs-timestudy. A skin-conditioningstudy was also done.
Hamster ear skin wastreatedin vivowith daily applications(10 Ixl/ear)of mineral oil
for two weeks.Animalswerethensacrificed
andTEWL determined
for the previously
treated and untreated contralateral ear skins.
APPARATUS
PREPARATION
Syriangoldenhamsterswere sacrificedby meansof an intraperitonealinjectionof sodium pentobarbital(65 mg per animal). The earswereremovedby incisionat the base
with the aid of surgicalscissors.
The dorsalear skin wasgently pulled awayfrom the
supportingcartilage,starting at the baseand extendingdistally. The cartilagewas
gently scrapedoff with a scalpelfrom the ventral side. A 10-mm diameterdermal
punchwas taken from the centerof the strippedskin sample.A photographof the
teflon cell usedfor in vitroTEWL studiesis shownin Figure 1. The cell wasequilibratedto constanttemperature
at 32øCusingheatedwaterpumpedthroughan aluminum holdingblockfrom a 35øCwaterbath or from a temperature-controlled
incubator. The 10-mm punchbiopsyof the skin wasplacedventralor hairysideup on the
lip or edgeof the donorcompartment
andthe top holderwasscrewed
tightly into place.
The insidesectionof the top wasfreeto rotatesothat the top couldbe securedwithout
twistingthe skin. The exposed
areaof the skinwasapproximately
0.32 cm2.
With the membranetightly fitted in place,onesideof the side-armopeningwasclosed
with a petrolatumplug. The donorcompartmentof the experimentalcell (sectionunderneathskin) was filled from the oppositesidewith approximately150 IxL of 100
IxCi/ml solution(2.2 X 108dpm/ml)containingtritiatedwater(HTO). This sidewas
also closedwith a petrolatum plug. A yellow Eppendorfpipet tip with a 5.0-mm
sectioncut off from the bottom and, subsequently,
attachedinto a 10-mm length
sectionof ¬" O.D., Vs"I.D., V•6"wall Tygontubingservedasthe receptor
compartment. The Tygon tubing end wasattachedto the screwedtop portionof the diffusion
cell (seeFigure 1). The receptorcompartment
wasfilled with approximately
0.24 g of
granular,anhydrouscalciumchloride,and the top coveredwith Parafilm.The cell was
returnedto the heatedaluminumholdingblockor the incubator,and the desiccant
was
removedor exchangedaccordingto the time specified.The desiccantwasplacedin a
20-mL scintillationvial and dissolvedin 2 ml of purified water. A 500-uL aliquot
samplewas then placed into a new vial, dissolvedin 10 mL scintillation cocktail
(Aquasol-2,New EnglandNuclear, BostonMA), and countedfor tritium contentfor
oneminutein a ModelSL400Intertechnique
scintillationcounter.
A knownvolumeof HTO wasdissolvedin water and the countsper minute (cpm)
determinedby scintillationcounting.This wasdesignated
asthe reference
standard.A
background
countwasdeterminedfor a volumeof waterandsubsequently
subtracted
from the count for the reference standard. Both the reference and the blank standard
had the sameconcentration
of dissolved
calciumchlorideas the sample.This wasto
eliminateerroneous
valuesdue to quenching.The cpm wasdeterminedfor the known
volumeof HTO anddividedby densityto determinethe cpm/weight.An HTO count
value was determinedfor sampleand divided by the referencevalue, the time, and
membraneareato determinethe TEWL in Ixg/cm2/hr.Six replicates
wereprepared.
METHOD
FOR TRANSEPIDERMAL
WATER
LOSS
111
A. Receptorcompartment
B. Donor compartment
C.
Parafilm
seal
D. Receptor
compartment;
filledwith calcium
chloride.
E. "Screw-in" attachment; functions to secureskin
and hold receptorcell.
F. Skin membrane;placeduponsmallwell of water
which functionsas donorcompartment.
Figure I. In vitroTEWL apparatus,representing
a modificationof Bronaugh's
flow-throughdiffusioncell.
112
JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS
RESULTS
AND
DISCUSSION
METHODOLOGY
Calciumchloridewaschosenasit is the mostconvenientdesiccantavailablefor study.
Five individualmeasurements
weremadeof the amountof anhydrous
calciumchloride
placedin the receptorcompartment
of the cell. The averageweightrecordedwas0.24
+ 0.016 g.
Cartilage-stripped
hamsterearmembraneis a newsourcefor obtaininga freshsampleof
full-thicknessskin membrane.Percutaneous
absorptiontheorystatesthat the flux is
inverselyproportionalto skin thickness(10). In actuality,we are referringto the thicknessof the stratum corneum,asthis is the rate-determiningskin layer. Measuredskin
thickness was 0. 181 --- 0.003 mm. Since little or no variation in skin thickness was
observed,it wasassumedto be a constantwhen measuringTEWL.
TIME
STUDY
Two blank and six experimentalcellswere preparedand placedinto the heatedaluminum holding block at varioustemperatures.The receptorcompartmentcontaining
the desiccantwas exchangedfor a fresh sample at the following time intervals:
0,0.5,1,2,3,4,5,6,7,8, and 20 hours.The TEWL flux wasdeterminedby calculating
the cumulativecountsat the particulartime interval.
A plot of the rate of TEWL-vs-time is shownin Figure 2. It wasobservedthat at 0.5
hourandonehour,the rateincreased
rapidlyfrom340 Ixg/cm2/hr
to 460 Ixg/cm2/hr,
and then the TEWL decreased
after two hours. Equilibrium was reachedbetweenthe
third and sixth hour. The apparatusoperatedin the presence
of a dry atmosphere
(less
than 25 percentrelativehumidity), determinedby a cobaltchloridepapertechnique
500
400
500
0
1
2
3
4
5
6
7
8
Time (hours)
Figure 2. TEWL rate vs time. Bars refer to standarderror of measurement.
20
METHOD
FOR TRANSEPIDERMAL
WATER LOSS
113
adaptedfrom Solomon(36). Sincethe apparatusoperatesin the presence
of a dry atmosphere,this transittime periodresultsin an initial evaporation
of waterfrom the membrane.Initially, the membraneis fully hydrated,swollen,and is morepermeable.This
providesan "increased
push"effectto passwaterthroughthe membranetowardsthe
anhydrous
desiccant.This transittime periodis designated
the "burst"effect.At steady
state, the amount of water adsorbedonto the desiccantis in equilibrium with the
amount abovethe membrane.Also, the membraneis approachinga drier state and is
lesspermeable.
EquilibriumTEWL rateaftersix hourswasapproximately
300 Ixg/cm2/hr
at 32øC.
Table I summarizes
previouslyreportedTEWL valuesbaseduponthe variousin vitro
techniques
currentlyemployedfor measurement.
Blank (1,2) utilized full-thicknessskin membranefrom the human abdomenin his
studiesand reportedTEWL valuesof between130 and 270 Ixg/cm2/hr
(23øC,23%
RH). Our valueof 152 Ixg/cm2/hr(22øC, 20-25% RH) for the hamsterskin is in
excellentagreementwith Blank'svaluefor humanskin.
TEMPERATURE
STUDY
A plot of TEWL rate-vs-temperature
is shownin Figure 3. An exponentialincreasein
TEWL wasobserved,which impliesthat watervaporpermeates
by a diffusionalpro-
cess.The TEWL ratebetween5 and 12øC,however,showedlittle change.
Table
I
Summary
of Transepidermal
WaterLoss(TEWL) RateDataforVariousIn VitroSkinModels
Refer-
Investi-
gator
Blank
Mali
Mali
Reiger,
Year
ence
1952
(1,2)
1956
1956
1974
(8)
(8)
(30)
Membrane
used
Method
TEWL
Temper-
rate
ature
(•g/cm2/hr)
øC
Relative
humidity
in %
100-200
23
40-50
thickness skin
130- 270
23
20-30
from abdomen
400-800
35
57
500-600
21
Human, full-
Gravimetric
Human,epider-
Gravimetric,
mis from trunk
desiccator
Human, epider-
Gravimetric,
mis from sole
desiccator
Human, stratum
Gravimetric
0
21
0
21
0-20
251
130
21
21
4O
85
21
3000
250- 300
corneum from
Deem
abdomen
Wu
Blank
1983
1984
(19)
(33)
Fetal hog
periderm
Human, stratum Saturated
salt
comeurn
et al.
Saturated
salt solutions
work
1987
Hamster ear,
full-thickness
skin
3O
600-1200
30
0-80
250-300
32
20-25
152
22
20-25
solutions and
tritiated
This
5O
water
Tritiated water
114
JOURNAL OF THE SOCIETYOF COSMETICCHEMISTS
500
400
lOO
0
I
5
10
15
20
25
:50
:55
40
Temperature øC.
Figure 3. TEWL rate vs temperatureat steady-state
conditions(after 3 hours).Barsreferto standarderror
of measurement.
If the reciprocal
temperatures
in degrees
Kelvinareplottedvs the naturallogarithmof
the TEWL rate in the temperature
rangesbetween12 and 37øC,linearityis observed
(Figure4). It is difficultto explainthe lackof linearityat 5øC.The waterpermeation
may have been disruptedat this near-freezingtemperature.The energyof activation
was calculatedby slopeanalysis.Our calculatedvalue of 13.1 Kcal/molecompares
favorablywith an activationenergyvalue of 15 Kcal/mole previouslyreportedby
Scheupleinfor human skin (9).
MOISTURIZER
STUDY
Four experimentalcellsand two blank cellswerepreparedfor eachmoisturizingagent
tested.Ten •L of eachagentwasappliedto the top of the membranesurface,prior to
attachmentof the receptorcell filled with desiccantand placementof the unit into the
32øCheatingblock.Plotsof TEWL-vs-timevaluesfor membranes
treatedwith various
potential moisturizersare shownin Figures5 and 6. The figuresshowindividual
TEWL valuesvs time overa 24-hourtime periodfor the untreatedsampleand skin
treated with agents. The untreatedsampleshowsa result similar to that reportedin
Figure 2. Transepidermalwater lossreachessteady-stateconditionsafter three hours,
exceptfor that sampletreatedwith 25% glycerin.
When comparedto the untreatedsample,castoroil is the only agentthat exhibiteda
"burst"effect.Skin treatedwith sesame
oil, mineraloil, and 25% glycerinin waterall
appearto inhibit this effect. Satoand Nagai (37) comparedthe effectsof different
METHOD
FOR TRANSEPIDERMAL
WATER LOSS
115
m
O-•
5.0
mmm
•mmm
m•
4.0
ecipr0cl of
Kelvin
Temperature
X10
z
Figure 4. Naturallogarithmof TEWL vs reciprocal
of absolutetemperaturex 1000.
emollientmaterialson TEWL usinga silasticmembrane.Therewasa goodcorrelation
between the TEWL rate for this in vitro model and the TEWL rate for an in vivo human
skin model. They foundthat the decrease
of TEWL rate that resultedfrom emollient
applicationwasinverselyproportionalto the polarityof the materialapplied.In other
words,the morepolarthe materialappliedto the membrane,the greaterthe TEWL
rate. Mineral oil is the leastpolar substance
that we testedand it inhibited TEWL the
most.At steadystate,the effectof castor-oil-treated
skin on TEWL (Figure6) was
similarto that of sesame-oil-treated
skin (Figure5).
Glycerin,whichactsto bindwaterto the skin,produced
an interestingeffect.During
the first two hoursglycerinactedasan occlusive
agent,sinceTEWL valueswereclose
to that of mineral-oil-treated
skin. After fourhours,however,the glycerin-tissue
compositewasobserved
to become
saturated
with water.At thesix-hourtimepoint,TEWL
rateswere almostdoublethoseof untreatedskin. This is comparable
to the results
obtainedby Reigerand Deem(30) who foundan increase
in the TEWL rate upon
applicationof 25% glycerinin water. Reiger and Deem showedthat hurnectants,in
general, increaseTEWL rate at low relative humidities.
116
JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS
ß
Untreated
o
Mineral
A
Sesame Oil
Oil
[] Glycerin
500
400
$oo
200 100 0
i
2
5
4
5
6
7
24
Time (hours)
Figure 5. TEWL ratesvs time valuesfor untreatedskinandskintreatedwith mineraloil, sesame
oil, and
25% glycerinin water. Barsreferto standarderrorof measurement.
A two-weekconditioningstudywascarriedout with mineraloil, the mosteffectiveof
the occlusive
agentstested.This testprovideduswith someinsightinto the mechanism
of mineral oil as a moisturizer.Resultsof this study are reportedin Table II. No
significantdifferences
were foundbetweentreatedand untreatedear skin samples.It
was concludedthat for mineraloil to act to decrease
TEWL rate in this procedure,it
must be able to bind to the skin. The protectiveeffectsof mineral oil were experimentally removedduring samplepreparation.Thus we concludethat mineral oil actsto
decrease
TEWL by impartinga physicalbarrierto the transportof water from the
membrane.Conditioningthe skinwith mineraloil appeared
to be an ineffectivetreatment modality.
CONCLUSIONS
Previouslydevelopedin vitrotechniquesfor measuringTEWL are tediousand timeconsuming.Most of thesein vitromethodsemploya gravimetrictechniquefor measurement. SteadystateTEWL ratescannotbe achievedin lessthan 24 hours.Blank'sin
vitromethod(30) of usingtritium-labeledwater to measurewater losswas combined
METHOD
FOR TRANSEPIDERMAL
ß
WATER
LOSS
117
Untreated
•- t vCastor
Oil
E-= 500
.a 4oo-
.....
•._. 300
•- o
o._j
200
100 o
1
2
3
4
5
6
7
24
Time (hours)
Figure 6. TEWL ratesvs time valuesfor untreatedskin and skin treatedwith castoroil. Barsrefer to
standard error of measurement.
with adsorption
of waterontoa desiccant.
The newmethodprovedto beveryefficient.
TEWL equilibriumcouldbe achieved
within threehoursanda full studycanbe completed within eight hours.
Cartilage-stripped
hamsterear skin wassuccessfully
usedasan in vitromembranefor
TEWL measurement.
The barrierproperties
of thehamsterearskincompared
favorably
to thoseof humanskin. TEWL ratevaluesagreedwith valuespreviously
reportedfor
human skin obtained under similar environmentalconditions(1,2). The membrane
exhibitedan exponential
increase
in TEWL with increased
temperature.A calculated
energyof activationfor waterpermeation
of 13 Kcal/molewasin generalagreement
with the valuereportedpreviouslyby Scheuplein
for humanskin (9).
Table
II
Transepidermal
Water LossValuesfor Mineral Oil ConditioningEar After VariousTime Periods
Time Periods:
1 hr
3 hr
6 hr
24 hr
268
2O6
Treated Ear
Mean
TEWL
I-tg/cm2/hr
391
269
Untreated
Ear
Mean
TEWL
}zg/cm2/hr
437
p > 0.3
315
p>
0.3
226
p > 0.3
2O2
p>
0.3
118
JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS
The presentin vitrotechniquepotentiallycanalsobe usedto evaluatethe relativeeffectivenessof skin agents. This method has a real advantagein that the tritium-tracer
techniquecaneliminateerroneous
TEWL valuesthat may resultfromwaterevaporation
froma moisturizer.In general,it wouldappearthat TEWL is influencedby the polarity
of the agentappliedto the skin. The mostnonpolarof the four agentstested,namely
mineral oil, showedthe lowestTEWL rate. In contrast,the humectant,(25% glycerin
in water)-treatedskin, showedan increasein TEWL rate. Our TEWL ratesfor glycerin
were comparableto data previouslyreportedby Reiger and Deem (30). Occlusive
agents,suchas mineral oil, showedevidenceof decreasingwater lossby acting as a
physicalbarrierto the transportof water throughthe membrane.
Furtherworkis deemednecessary
forprovingthevalidityof thismethodasa pretestfor
moisturizerefficacy.
REFERENCES
(1) I. H. Blank, Factorswhich influencethe watercontentof the stratumcorneum,
J. Invest.Dermatol.,
18, 433-439 (1952).
(2) I. H. Blank, Further observationson factorswhich influence the water content of the stratum cor-
neum,J. Invest.Dermatol.,21, 259-269 (1953).
(3) N. Brudney,M. Leduc,and B. Turek, Effectsof vehicleson percutaneous
absorption,Cosmet.
Toilet.,
93, 53-66 (1978).
(4) H. D. Onken and C. A. Moyer, The water barrierin humanepidermis,Arch. Dermatol.,87,
584-590 (1963).
(5) R. J. Scheuplein
and I. H. Blank, Permeabilityof the skin, Physiol.Rev., 51(4), 702-747 (1971).
(6) H. BakerandA.M. Kligman, Measurement
of transepidermal
waterlossby electricalhygrometry,
Arch. Dermatol.,96, 441-452 (1967).
(7) G. E. BurchandT. Winsor,Rateof insensible
perspiration
(diffusionof water)locallythroughliving
andthroughdeadhumanskin,Arch.Intern.Med.,74, 437-444 (1944).
(8) J. W. H. Mali, The transportof water through the human epidermis,J. Invest.Dermatol.,27,
451-469 (1956).
(9) R. J. Scheuplein,
Mechanisms
of percutaneous
absorption.I. Routesof penetration
andthe influence
of solubility,J. Invest.Dermatol.,45(5) 334-346 (1965).
(10) R.J. Scheuplein
and R. Bronaugh,Biochemistry
andPhysiology
of theSkin(OxfordUniversityPress,
1983), pp. 1255-1295.
(11) S. Nacht, Skin frictioncoeffient:Changesinducedby skin hydrationand emollientapplicationand
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