changes in epidermis and transepidermal water loss

j. Soc.Cosmet. Chem.,48, 219-234 (September/October 1997)

Correlation between surfactant-induced ultrastructural

changesin epidermisand transepidermalwater loss MANOJ MISRA, K. P. ANANTHAPADMANABHAN, KAREN HOYBERG, RICHARD P. GURSKY, SEAN PROWELL, and MICHAEL ARONSON,

UnileverResearch

US, 45 RiverRoad,Edgewater, NJ 07020. Accepted for publication October 31, 1997.

Synopsis A comparativeanalysisof surfaceand ultrastructuralchangesin stratumcorneum(SC) with transepidermal waterloss(TEWL) wasconducted to developa betterunderstanding of the surfactant-induced damageto humanskin.Treatmentscompriseda synthetichnionicsurfactant(A), a compositionof soap,glycerin,and petrolaturn(B), a pure soap(C), and water (control).An increasein water lossis shownto correlatewith increased perturbationof lipid barrierand damageto multiple layersof corneocytes. Transmission electron microscopy(TEM) revealedthat, in general,one to two layersof lipid lamellaeenvelopedthe outer layers of SCthroughoutthe tissue.A significantlylargernumberof lamellae(approximately six to eight) appeared only in the lower layers.Surfacetopology,obtainedusingenvironmentalscanningelectronmicroscopy (ESEM),displayeda normalunperturbedstructure.Treatmentwith A did not resultin significantchanges in SC. B causedregionalvariationsin corneocytes and an increasein TEWL. Treatment with C exhibited significantvariationin TEWL numbers:lipid lamellaeweredisorderedand corneocytes appeareddamaged

andswollen. Intercorneocyte damage ranged fromoneto two(forTEWL - 11 g/m2 hr) to up to sixcell layers (forTEWL- 34 g/m2 hr)oftheSC.Thepresence orabsence of theoutermost layers ofdisjunctum did not appearto be critical for water loss,presumablydue to a decrease in lipid lamellae.

INTRODUCTION

Mammalianepidermalcellsexist in a stateof constantrenewal.The processof differentiationstartswith the embarkationof the basalcellson a well-orchestrated path of terminal differentiationthat culminatesin the formation of the outermostlayer of stratifiedepithelialcellscalledstratumcorneum.The architectureof the stratumcorneumis oftenschematically comparedwith a brick wall patternin which the corneocytes (analogous to bricks)lie embeddedin a "mortar" of intercellularlipid-rich domains(1). The lipid milieu is highly complexandcomprises ceramides, cholesterol, andfatty acids. Cholesterolsulfate,glucosylceramides,and phospholipids exist in small amounts(2). Intercellularcontactis facilitatedby the presence of desmosomes, which form junctions betweenneighboringcells(3). Dependingupon the presenceor absenceof interlayer desmosomes, the stratum corneumcan be further subdividedinto compacturnand 219

220

JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS

disjunctum regions, respectively. Degradation ofdesmosomes isbelieved to beprimarily responsible for the desquamation of the outercorneocyte layers. Someof the importantrolesof the stratumcorneum areto preventthe desiccation of underlying regions, providemoisture retention, andrestrictthepercutaneous absorption of extraneous substances. Thewatercontent of thestratumcorneum is dependent upon the quantityof waterdiffusinginto thecorneum fromunderlying layers,its abilityto retainwater,andthe amountof waterlostdueto evaporation. The barrierpropertyof thestratumcorneum (barrierto waterloss)isbelieved to residein theintercellular lipid lamellae(4) that forma highlyordered,impermeable membranous structurebetween the corneocytes. An increasein water lossmay occureither as a result of decreased

ambienthumidityor bysurfactant-induced cellularperturbations. Dry skinisattributed to defective desquamation, but the mechanisms responsible for surfactant-induced dry skinarenotwellunderstood. Although theintercellular lipidsareconsidered responsible forthebarrieractionofskin,noconsensus hasemerged regarding therolethatthelipids play in dry skin conditions (2). Damageto the ultrastructure of epidermis hasbeen shownto causedecreased waterretentionpropertiesof the stratumcorneumandabnormal scaling(5-6).

Our currentunderstanding of the influence of surfactants on stratumcorneum lipidsis notclear,asconflicting evidence exists in theliterature. Forexample, depletion oflipids in surfactant-exposed (7) or solvent-exposed skin(8) is believedto be responsible for increased waterlossandfor dry skin conditions. On the contrary,Fulmerand Kramer (9) reportedthat the effectof sodiumdodecylsulfate(SDS)on stratumcorneumdid not resultin lipid depletion. However,significant differences in specific lipid classes were observed. Similarly,lackof damageto lipidswasalsoreportedby Fartasch etal. (10), who observed the presence of intact lipid lamellaein the outerlayersof surfactanttreated stratum

corneum.

The presentin vitrostudyattemptsto correlatethe ultrastructure of thestratumcorneum

with its waterretentionproperties and the integrityof the barrierafterexposure of humancadaverskin to threedifferentsurfactantsystems. The observed ultrastructural preservation of lipidsandcorneocytes (usingTEM) andsurface features (usingESEM) was correlated with

TEWL.

MATERIALS

METHODS

TREATMENT,

AND

WASH, AND TEWL MEASUREMENTS

A 4" x 8"pieceofabdominal skinfroma 31-year-old Caucasian malewasmounted (after the removalof the adipose tissue)on an in vitroskin-washing device(11), andthe ends of theskinweresecured. Thetemperature of thereservoir wasmaintained at 37øCusing a circulating waterbath.Thesurface of theskinwasdividedintofourequalsections for test treatmentsusingwaterand threeformulations (TableI). BaselineTEWL readings weretakenat eightsitesin eachsection. Skinsections weresubjected to thefollowing washprocedure: (a) The sectionwassoaked for 15 s underrunningtap waterat 40øC; (b) thetestbarwaswettedunderrunningtapwater(40øC)androtatedtentimesin the palm;(c) theproductwasappliedto thesurface of the skinwith fingersfor 2.0 minutes

SURFACTANT-SKIN

INTERACTIONS

Table

I

Principal Constituentsof Different Formulations Product

Main

Formulation A: Isethionatebar

Formulation B: Glycerin-oil bar Formulation C: Pure-soapbar

constituents

Fatty acid isethionate,stearicacid, sodiumtallowate,sodium isethionate,coconutfatty acid, sodiumsterate,sodiumalkyl benzenesulfonate,water, sodiumcocoate,fragrance Sodiumtallowate/cocoate, glycerin,almond oil, water Sodiumcocoate,sodiumtallowate,water, fragrance,sodium chloride

using a back-and-forthmotion, with fingersrewettedafter one minute; (d) post-wash, the skinsurfacewasrinsedwith runningtap water(40øC)for 30 seconds; (e) steps2, 3,

and'4wererepeated fora totalof 15 washes; (f) afterthefinalwash,thesurface of the skin waspatted dry usinga papertowel. The apparatuswasallowedto equilibratefor onehour. Subsequently, TEWL measurements weretaken from the sitesusedfor baseline. The difference between the initial and final values, the delta TEWL value, is

presentedin Table II. ENVIRONMENTAL

SCANNING

ELECTRON

MICROSCOPY

Four 1-cm biopsiesfrom eachpieceof treatedskin were examinedin the ElectroScan Model E-3 ESEM. Since no specimenpreparationis required for observationusing ESEM, the biopsieswereplacedon a 1-cm aluminumstub for examinationin a moist environment.The microscope(equippedwith a Peltier coolingstage)was operatedat -8øC, and a chamberpressurewas maintainedat 7.3 Torr. All sampleswere viewed at an acceleratingvoltageof 10 kV. TRANSMISSION

ELECTRON

MICROSCOPY

Smallpiecesof skin (-1 x 2 mm) weredissected from eachpieceof exposedtissuethat corresponded to variousTEWL values.Tissuepieceswere fixed overnightat 4øC in Table

II

Transepidermal Water Lossof TissueExaminedby TEM or ESEM

A TEWL in g/m2 hr Specimen no.

Water

Formulation A

Formulation B

Formulation C

Technique

1 2 3 4

0.37 0.64 1.03 1.59

1.61 2.02 2.56 2.86

2.12 2.30 2.76 3.98

11.53 16.65 32.67 34.52

TEM

5 6 7 8

0.49 0.56

1.17 1.61 3.05 3.80

2.54 3.93

6.39 8.99 22.34 58.35

ESEM

0.66

0.92

4.10

4.79

222


2.5% glutaraldehydein 0.1 M sodiumcacodylatebuffer (pH 7.2). After extensive washing,tissuepieceswerepost-fixedin eitherbuffered1% osmiumtetroxide(30 min) or 0.5% rutheniumtetroxide(15 min). Sampleswererinsedin threechangesof buffer beforedehydrationin a gradedconcentration seriesof acetone.Specimens wereembeddedin Spurrresinandincubatedat 60øCfor two days.Ultrathin sections werecut from the hardenedblocks,mountedon carbon-coated coppergrids, and post-stainedwith uranylacetateandleadcitrate.The specimens wereexaminedin a JEOL 1200 EX TEM.

RESULTS

TEWL

TEWL measurements were obtainedat eight sites for each of the treatments,and specimens weredividedfor furtherstructuralstudiesusingTEM andESEM(TableII). The distribution of TEWL measurementswas narrow for tissue exposedto water, formulation A, and formulation B. The respectivemean (+SD) valuesof TEWL were

0.78 + 0.4 g/m2hr(water),2.3 + 0.8 g/m2hr(formulation A), and3.3 + 0.9 g/m2hr (formulation B). On the other hand, tissue treated with formulation C exhibited the

highest TEWLvalues andshowed significant site-to-site variation (24 + 16g/m2hr). TEM

AND

ESEM

Water-washed controlskin.Epidermis,in a water-washedcontrol specimen(Figure la), consistsof the inner and outer layersof stratum corneum(compacturnand disjunctum).

Disjunctureis characterized by the absence of interlayerdesmosomes. In contrast,the corneocytes in successive layersof compactumexhibit the presence of interlayerdesmosomes.The statusof desmosomes may differ dependingprimarily upon the extent of degradationcausedby desquamating enzymes.The intercellularspaceis generallyoccupiedby sheetsof lipid lamellae(12), the numberand integrity of which vary from regionto region.The outermostlayersof the disjunctumnormallydisplayeda thin sheet of lipids comprisingone to two layers(Figure lb). Departuresfrom this normalouter stratumcorneumstructurewereoccasionally observedin thoseregionsof water-washed tissuewhere stratum corneumappearedeither totally or partly devoidof disjunctum (Figure lc). The outer lipid layers, in such regions,displayedrobust structuresof well-formedmultilayers(five or six) that extendedaroundand betweendesmosomes (Figure ld). In general,the numberof lipid lamellaewerelargerin the lowerlayersof corneocytes, which alsodisplayeda greaternumberof interlayerlipid-envelopeddesmosomes. A majority of the tissue,however,displayedintact disjunctum,with very few lipid layerscoveringthe outer corneocytes. Multilamellar lipid layerswere seenenveloping only 20-30% of the surfacecorneocytes. Structurally,the intercellularproteins and cell envelopeappearednormaland remainedunaffectedby treatment.TEWL values for water-washedtissuepiecesdid not show significantsite-to-sitevariation.This is confirmedby the uniformityof the structuralpreservation observedin differentpieces of tissue.Even in the 20-30% of the region that displayeddamageddisjunctum,the intactlipid multilayerswerepresumably sufficientto maintainbarrierproperties. ESEM showedthat the surfacetopographywas fairly smooth(Figure 7a), the individual cor-

SURFACTANT-SKIN

INTERACTIONS

223

neocyteswere hardly visible, and very few corneocytes displayednoticeableuplifting (uplifted corneocytes appearbrighter with greatercontrast). Formulation A-treatedskin.The overallultrastructuralmorphologyof skin exposedto the isethionatebar (formulationA) appearedvery similar to that of the water-washed skin. However, in general,fewer cell layerswere presentin the disjunctum/compactum regions (Figure 2a). Thin lamellar sheetsor multilayer lipid regionswere seenin both formulationA- andwater-treatedskin.The lipid lamellaein the outerlayerswereoften presentasuniform,4-8 layersthick, well-definedextendedregions(Figure2b) and, as in the water-washedspecimens, theseregionsbelongedto the lower layersof stratum comeurn,often in compacturn.The integrity of proteinswithin the cell and the cell envelopewas noticeablyunaffectedby the treatment. FormulationA-treated skin exhibited somewhathigherTEWL valuesthan water-washed skin. This differencemay be due to an overall reductionin the number of cell layersand a resultantdecreasein the thicknessof the corneum.Corneocyte sizewasunaffected.The surfacetopography(Figure 7b) was smooth,with a few uplifted corneocytes visible. Formulation B-treatedtissue. The glycerinbar (formulationB)-treatedspecimenwassimilar to the skin specimentreatedwith the isethionatebar. The number of cell layersin the disjunctum/compactum region was variable.Although the majority of the tissue displayedthe normal morphologyof lipid lamallae,evidenceof disorderwithin the lamallae could occasionallybe seen(Figure 3a,b). Generally, the organizationof cell envelopeand proteins was unaltered. In certain cases,however, the tissue displayed significantdisruptionof proteinsand lipids (Figure 4a,b). The intercellularlipids in adjacentouter layerswere either absentor displayeddisorderedstructures.Damageto cellularregionswas evidentin the form of large, globular, low-densityregions,which oftendisplayedlipid-like structures (arrows,Figure4b). Suchdamagewasalwaysconfined to the outermostlayer of the epidermis.FormulationB-washedtissueappeared somewhatmore damagedin comparisonto either control or to formulation A-treated tissue.This wasreflectedin termsof somewhatlargerTEWL values.ESEM observations alsoshowedthe presence of a greaternumberof upliftedcorneocytes comparedto control (Figure 7c).

Formulation C-treatedtissue. The soapbar (formulationC)-treated specimenexhibited maximum ultrastructuraldamageto cellular proteinaceousmaterial, envelope,and lameliar lipid structures.The presenceof disjunctumcould be seenonly in about 5% of the treatedtissue(Figure5a).Most of the tissuedisplayedabsence ofdisjunctumandloss of a few layersof compacturn.Lipid structurein the outer layerswas often severely damaged.Orderedlamellarstructureswere replacedby amorphousmaterial. Suchregionsoften coexistedwith poorlyorderedlipid-like structures(arrows,Figure 5b). This could be due to the intercalationof detergentin lipid layers.Intracellulardamageto proteinswas similar to that describedfor formulationB exceptthat the damagewas much more extensiveand severein the formulation C-washed tissue (almost 25% of the

formulationB-washedtissueand 100% of the formulationC-washedtissuedisplayed intracellulardamage).The damagedcells appearedthree to four times wider than the controlcells(Figures6a, lc). TEWL measurements showedsignificantsite-to-sitevariation.The lowestTEWL value

fortheskinexamined usingTEM was11g/m2 hr.Damage in thiscase wasconfined to thetoptwolayers ofcorneocytes. Specimens thatshowed largewaterloss(-35 g/m2 hr)

224


.

o

Figure 1. (a) Low magnificationoverviewof water-washed tissuedisplayingthe separation betweendisjunctureand compactumregionsof SC. Disjunctureis characterized by the absence of interlayerdesmosomes(arrowheads) (! ! 000 x). (b) Lipids coveringthe outermostcorneocytes of disjunctum(arrowheads) in controltissueshowfew multiple layersof orderedlameliarstructures(128,000x).

SURFACTANT-SKIN

INTERACTIONS

225

Figure1. (c) Water-washed controltissue showing thepresence of interlayer desmosomes (arrowheads) in the outerregionsof SC andabsence of disjuncture (24,000x). (d) Multilayeredlipid lamellae(arrows) enveloping theouterlayers ofcorneocytes anddesmosomes (arrowheads) wereseen in those regions ofcontrol tissuethat lacked disjuncture(128,000x).

226


-

-L

Figure 2. (a) FormulationA-treatedtissueshowingdisjunctum--compactum region(24,000x). (b) Wellpreserved,multiple layersof lipid lamellae(arrows)in lower layersof SC (128,000x).

exhibitedsignificantdamageto lipids andproteinsin the top 4-6 cell layersof stratum corneum(Figure 6a,b). Often, the entire disjunctumand most of the compacturnappeareddestroyed(Figure6c). Damageto the inter- and intracellularregionswasqualitatively similar in all the samplesirrespectiveof individual variationsin water loss. However, the extent of damage rangedfrom the top few layersto the deeperlayers,

SURFACTANT-SKIN

INTERACTIONS

227

Figure 3. (a) FormulationB-treatedtissueshowingdesmosomes (arrowheads) and disjunctum-compactum regionof the SC (24,000x). (b) Multiple layersof lipid lamellae(arrows)surroundingthe outerlayersof SC (128,000x).

dependingupon TEWL. ESEM micrographsshowedthat the surfaceof formulation C-treatedskin resembledthe surfacefeaturesof dry skin, i.e. a large numberof corneocytesdisplayeduplifted morphology(markedregions,Figure 7d).

DISCUSSION

This study provided an opportunity to examine the correlationbetween surfactant-

228


Figure 4. (a) Damageto outerlayersof corneocytes (arrows)wasseenin 25% of the formulationB-treated tissue(24,000x). (b) A highermagnification view of the damagedregionshowingfingerprint(arrows)of lipid-like regionssurroundingthe outer corneocytes (128,000x).

inducedstructuralchangesin epidermiswith TEWL. Different surfactanttreatments resultedin variabledegreesof lipid and corneocyte preservation. Most of the waterwashedtissue(control)displayedintactdisjunctumcomprisingfew layers(oneto two) of lipid coveringthe outercorneocytes. In contrast,isolatedregionsthat lackedmostof

SURFACTANT-SKIN

INTERACTIONS

229

b

Figure5. (a)Occasional presence ofdisjunctum informulation C-treated tissue (TEWL11g/m2hr).Outer lipid layers(arrow)weregenerallyfeatureless (24,000x). (b) Grossintracellular damage(arrowheads) and lossof intercellular lipids(arrows)canbe seenin this high-magnification view of formulationC-treated tissue (128,000x).

230


Figure 6. Swellingof the cellswasvisiblein the formulationC-treatedtissue(a). Damageextendedto deeperlayersof corneocytes. Often up to 4-6 cell layersweredamagedin tissuedisplayinghigherTEWL values(a and b). Extensivedamageoften resultedin the lossof mostof the cell layersof the SC (c); such

regions werepresent in tissue displaying highTEWL (-30 g/m2 hr).(24,000x[a andc], 128,000x[b].)

SURFACTANT-SKIN

INTERACTIONS

2 31

Figure 7. Representative ESEM picturesof the surfaceof tissuestreatedwith water(a), formulationA (b), formulationB (c), and formulationC (d). Arrowsshowthe uplift of the individualcorneocytes.

the disjunctumwere occasionally encountered. Suchregionsdisplayedmultilayersof intact sheetsof lipid lamellaearoundand betweenneighboringdesmosomes. Similar featureshavealsobeenreportedin sequentialtape stripsharvestedfrom normal skin, which revealedthat the multiple lamellaeexistedonly in the lower layersof stratum corneumand were absenttoward the surfacelayers(2).

FormulationA-treated skin was similar in morphologyto water-washedtissueexcept that regionsdevoid of disjunctureappearedwith increasedfrequency.Intracellular proteinsandextracellularlipidsremainedpredominantlyunaffected.Lipid lamellaewere multilayered and well-formed. The water loss did not significantly depend on the damageto the outer cell layers(which lack lipid lamellae),presumablybecauseof two reasons: first, the damageto outer layerswas commonto both water and formulation A-treatedpiecesof skin, andsecond,the TEWL valuesfrom differenttissuepieceswere fairly consistent.The generalstructureof formulationB-treatedtissuewas similar to formulationA-treated tissueexceptfor significantinter- and intracellulardamageto about 25% of the tissue noticed in the caseof formulation B. Lipids often lacked characteristicperiodicity in formulationB-treated tissue.TEWL valueswere modest. Regionalvariationin TEWL couldbe attributedto the damagedlipid lamallaeobserved in about 25% of the tissue.FormulationC-induceddamagewasubiquitousand severe, and resultedin lossof lipid structureaswell as intracellulardamageto proteins.Such

232


damagewasreflectedin high TEWL values.The natureof structuraldamagewassimilar in all specimens irrespectiveof individualvariationsin TEWL. The fact that only the

upperlayers appeared damaged in tissue displaying lowerTEWLnumbers (11g/m2 hr) in contrast to fourto sixaffected layers forhighTEWLnumbers (35g/m2 hr)indicates a direct relationshipbetweenthe extent of damageand water loss.

TEWL is generallyconsideredto be a passivediffusionphenomenon. AssumingFick's law of diffusionasa first approximation, diffusionof watercouldbe considered inversely proportionalto the distanceor the total thicknessof the corneum.However,water loss through the surfacelayersof corneocytes is not only inverselyproportionalto the thicknessof the epidermisbut alsodependsuponthe resistance to its migrationpathway providedby the barrierlipids. Both parameters(epidermalthicknessand lipids) were affectedby different surfactanttreatments.Although the epidermisoften displayed structuralvariabilityevenin water-treatedtissue,the decrease in corneumthicknesswas not significantenoughto affectTEWL, as was evident by the uniformity of TEWL measurements. Also, in water-treatedtissuethe lipids were well preservedin the lower layersof the stratumcorneum,providingan effectivebarrieragainstwater loss.Treatment with the isethionatebar resultedin an increasein the frequencyof occurrence of intact multilamellarlipid sheetscoveringthe uppercorneocyte layers.This suggests that the treatment with formulationA resultedin a reduction(comparedto control) in the outer layersof disjunctumand consequently causeda slight increasein TEWL. The water loss, however, remained limited due to the barrier offered by the surfacecontouringlameliarlipids.Glycerinbar-treatedtissuedisplayedfeaturessimilarto those describedfor the isethionatebar. However, the outer lipids displayeddamagedmorphology,i.e., non-lamellar,amorphous materialin about25% of the surfaceregions.It is tempting to suggestthat the modestincreasein TEWL in glycerinbar-treatedtissue couldbe ascribedto damagedlipids in the outer layersof surfacecorneocytes, but the relationshipis only directionalat best.Significantdependence of TEWL on the thinning of epidermisand disruptedlipid structureswas evidentin soapbar-treatedtissue.The disjunctumwascompromised in almost90% of the tissue.The lipid barrierunderlying the disjunctumwasseverelyaffectedand appearedasan amorphous non-lamellarstruc-

ture.In tissuedisplaying >30 g/m2 hr of waterloss,thestratumcorneum waspunctuated with regionsin which almost all structure above the viable cell layerswas disrupted(Fig. 6c).

The soapbar-treatedtissuerevealeda decrease in the numberof cell layersformingthe stratumcorneum,lipid loss,and significantswellingof the corneocytes. Someof the corneocytes werefour timeswider in projectioncomparedto the normalcorneocytes. A surfactant-induced increasein surfacearea and swelling is known to dependon the surfactanttype (13). Increasedpermeabilityof the cell membraneand consequent increasein the intracellularbindingof watermolecules may be responsible for the observed increasein the projectedwidth of damagedcorneocytes. An advantageof usingESEM for structuralstudiesis that the specimencanbe observed in its nativestatewithoutpreparationartifacts.However,the interpretationof the ESEM micrographs requiresa carefulanalysis. Normal, undamaged skin in ESEM appears asa smooth surface.In damagedskin, the structuralchangesto corneocytes appearas brighterregions.This couldbe attributedto the uplifting of cells,whichcauses changes in their geometricdisposition.Peripheriesof uplifted corneocytes appearbrighterthan surroundingregions.Such fine changesare often difficult to detect becausethe skin

SURFACTANT-SKIN

INTERACTIONS

233

surfaceis rarelyflat and signalvariationsfrom neighboring(-100 pm) regionsmay also contributeto significantintensityvariationsin the image.Therefore,extractionof fine structuralchanges(in individualcomeocytes) from grossintensityvariationsrequiresa carefulanalysisof the micrographs. The accuracyof TEWL measurementis dependentupon the amount of water loss. Measurements are highly reproduciblefor low-water-lossconditionssuchas thosethat

existin normal unperturbed skin.If thewaterlossisabout20 g/m2hr,themeasurement errorcouldbeabout10%.However, whenlosses approach 80 g/m2hr,theerrorcould exceed 50%(14).TEWLin surfactant-treated tissue maybeashighas60 g/m• hr, as wasseenfor soapbar-treatedtissue.However,the exactTEWL valueis not significant for the currentdiscussion, asthe dependence of structuraldamageon TEWL valueswas fairly consistent. The high degreeof water lossencountered in soapbar-treatedtissuemay be due to the combinedeffectof damageincurredto lipids and to the intracellularenvironment.This could also affect the water-retainingmechanismsinvolving the role of moleculesresponsiblefor providingnaturalmoisturizingfactor(15). Leachingof suchmolecules from surfactant-damaged corneocytes may aggravatedry skin condition. This studyshowedthat the presence or absence of outerlayersof disjunctum,whichhave minimal surroundinglipid, is not critical for water loss.Water lossdependedupon the preservation and integrity of lipids and proteinsbelongingto the lower layersof corneocytes.No severewater losswas observedin caseswhere the lipids in compactum appearedorderedand structured.Inordinatelyhigh water loss(for the soapbar) wasdue to damagethat extendedfrom the surfaceto multiple strataof underlyinglipids and comeocytes.

REFERENCES

(1) P.M. Elias,Epidermallipids:Barrierfunctionand desquamation,J.Invest.DermatoL,80 (Suppl),4449 (1983).

(2) A. V. Rawlings,A. Watkinson,J. Rogers,A. Mayo,J. Hope, andI. R. Scott,Abnormalitiesin stratum corneumstructure,lipid composition,and desmosomedegradationin soap-inducedwinter xerosis,J. Soc.Cosmet.Chem.,45, 203-220 (1994).

(3) S.J. Chapmanand A. Walsh, Desmosomes, corneosomes and desquamation. An ultrastructuralstudy of adult pig epidemis,Arch.Dermatol. Res.,282, 304-310 (1990). (4) P. Bowsenand R.J. White, Isolation,barrierpropertiesand lipid analysisof stratumcompacturn,a discreteregionof the stratumcorneum,Br. J. Dermatol.,112, 1-14 (1985). (5) G. Imokawa,K. Sumura,and M. Katsumi,Studyon skin roughness causedby surfactants. I. A new methodin vivo for evaluationof skin roughness,J. Am. Oil Chem.Soc.,8, 92-108 (1975). (6) G. Imokawa,Evaluationfor alterationof the stratumcorneum,J. Jpn. Cosmet. $ci. $oc.,8, 92-108 (1984).

(7) G. Imokawa,S. Akasaki,Y. Minematsu,and M. Kawai, Importanceof intercellularlipids in water retentionpropertiesof the stratumcomeum:Inductionandrecoverystudyof surfactantdry skin,Arch. Dermatol.Res,281, 45-51 (1989).

(8) G. Imokawa,S. Akasaki,M. Hattori, andN. Yoshizuka,Selectiverecoveryof derangedwater-holding propertiesof the stratumcorneumlipids,J. Invest.Dermatol.,187, 758-761 (1986). (9) A. W. FulmerandG. J. Kramer,Stratumcorneumlipid abnormalities in surfactantinduceddry skin, J. Invest.Dermatol., 86, 598-602 (1986). (10) M. Fartasch,T.L. Diegpan,O. P. Hornstein,Morphologicalchangesof epidermallipid layersof stratumcorneumin sodiumlauryl sulfateinduceddry skin,J. Invest.Dermatol.,96, 617A (1991). (11) K. P. Ananthapadmanabhan, S. Prowell, K. Hoyberg, M. Misra, S. Spaltro,S. Mukherjee,and M.

234


Aronson,Cleanser inducedstructuralchanges in humanstratumcorneum, Proceedings ofthe4th Congress of theEuropean Academy of Dermatology and Venereology, Brussels (Elsevier,Amsterdam,1995), p. 143. (12) K. C. Madison,D.C. Schwartzendruber, P. W. Wertz, and D. T. Downing, Presence of intact intercellularlipid lamellaein the upperlayersof the stratumcorneum, J. Invest.DermatoL,88, 714-718 (1987). (13) L. D. Rhein, C. R. Robbins,K. Fernee,and R. Cantore,Surfactantstructureeffectson swellingof

isolatedhuman stratum corneum,J. Soc.Cosmet. Chem.,125-139 (1985). (14) P. Elsner,E. Berardesca, and H. I. Mailbach(Eds.),Bioengineering of theSkin:WaterandtheStratum

Corneum (CRC, Ann Arbor, MI, 1994), Chapter5. (15) A. V. Rawlings,I. R. Scott, C. R. Harding, and P. A. Bowser,Stratum corneummoisturizationat the

molecularlevel,Prog.Dermatol.,28, 1-12 (1994).