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J. Soc.Cosmet. hem. 4 239-243 1973) 1973Society f Cosmetic hemistsf GreatBritain

The influenceof temperature ndhumidityon stratumcorneum ndits relationto skin chappingJ. D. MIDDLETON and B. M. ALLEN*

Presented n the 11th April 1972 in Oxford, at the Symposiumon' Skin--Environmental esponsesndprotection',organizedby the Society of Cosmetic Chemists of Great Britain.

Synopsis The susceptibility f the STRATUM CORNEUM to CHAPPING depends pon itsmechanical properties such as extensibility. It has previously been shown that at constanttemperature, xtensibilityof isolatedcorneum s related o RELATIVE HUMIDITY and thatat constant elativehumidity,extensibilityncreases hen he temperatures raisedabove25C.In this report extensibilityof isolatedanimal corneumhas been determinedat 5C whereskinchapping occurs more frequently. EXTENSIBILITY was found to be lower at reduced tem-peraturesalthough the corneumwater content did not decrease.t was concluded hat skinchapping s the result of a low corneumTEMPERATURE and WATER CONTENT and thatgreater laking and chappingof the surfacecorneum s a resultof a gradientof temperatureorwater content across he corneum n a cold or dry ENVIRONMENT.

INTRODUCTION

The function of the stratumcorneum s to protect the underlyingtissues rom desiccation nd from chemicaland physical nsult. To fulfilthese unctions t must form a continuousmembranewith a high degreeofflexibilityand elasticityo allowfor the movements f the skin. f flexibilityand elasticity re reduced he corneum ends o crackand flake. This con-dition is commonlyseen,particularly n winter weather,and is often re-ferredto as skin chapping.* Environmental afetyDivision, UnileverResearch aboratoryColworth/Welwyn,ColworthHouse, Shambrook, Bedford.

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240 JOURNALOF THE SOCIETYOF COSMETIC HEMISTSSeveral tudies ave nvestigatedhe factorswhichcontrol he flexibilityand elasticity f the corneum.Blank (1) was he first o observe ubjectively

that water was an important factor in the flexibility of human callus andthat the water contentof isolatedcallusdepended pon the relativehumi-dity (rh) of the atmosphere.he dependencef water contentof isolatedcorneum on rh was later confirmed by Singer and inson (2) and byMiddleton (3) usinganimal corneum.The dependencef the elasticproperties f corneumon rh wasdemon-stratedby Middleton (3), who showed hat extensibility f isolatedanimalcorneum ncreasedwith increasing h. Wildnauer, Bothwelland Douglass(4), working with isolatedhuman corneum,showed hat elongationofstratum corneum strips at fracture increased with increasingrh. Thebreakingstrengthdecreased ith increasing h, but the work required ofracturea strip ncreased ith increasing umidity.The dependence f corneumwater contentand elasticpropertiesonhumiditysuggestshat the incidence f skin chapping houldbe related ohumidity.Gaul and Underwood 5) showed hat the incidence f chappingwas greater at low absolutehumidity (dew point) and was not related torh. However, Singerand Vinson 2) showed hat corneumwater contentwasrelated o rh and not to absolute umidity.Middleton 6) pointedout thatin Gaul and Underwood'sobservations5) low absolutehumidity onlyoccurred t low temperature nd showed hat, at temperaturesreater han25C, corneumextensibilityncreasedwith temperatureunder conditionswhere water content did not increase. It was concluded that corneum ex-tensibility,and hence he incidence f chapping,wasdependent pon bothrh and emperature. ur previousmeasurementsn theeffect f temperature(6) wererestrictedo temperaturesreater han ambientand in this paperwe report he effectof lower emperaturesn the regionwhereskinchappingnormally occurs.

EXPERIMENTAL

Stratumcorneum rom the rear footpadsof guinea-pigs as used.Themethodof separation asbeen eportedpreviously 7). From eachpieceoffootpad corneuma strip measuring .6 by 1.5 cm was cut with a stainlesssteel punch. Extensibility was measured on an Instron Tensile Tester.Details of the techniquehave been describedpreviously 3). A strip ofcorneumwas clampedbetween wo pairs of jaws and stretched t a con-stant rate of extension. The load is measured on a tension cell and the

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INFLUENCE OF TEMPERATURE AND RH ON STRATUM CORNEUM 241

load-extensionurveplottedautomatically n a recorder. rom the slopeof the nitial part of the curveextensibilityanbe calculated nd expressedas percentage xtension100 g- load.Duringextensibility easurementsemperature ascontrolled y meansof a specially onstructedabinetLEC Refrigeration td, BognorRegis).This cabinet,with gloveholesat the front, surroundedhe jaws of thebstronand had aperturesat top and bottom to allow free movementofthe jaw attachment o tensioncell and crosshead. elativehumiditywasnot controlled ut wasmeasured ith a wet anddry bulb thermometer ith-in the chamber. hroughout achexperimentemperatureid not vary bymore han -4-1Cand rh by more han + 3o.Before measuringextensibility he corneumwas preconditioned yequilibratingn a desiccatorversaturated otassiumromide81 rh at25C) or 6 days. t was henplaced n the chamberon the Instronand eftto equilibrateo therequiredemperatureor at least20 min beforestartingmeasurements.

Water binding was measured y comparingwet and dry weightsaspreviouslyescribed3), afterequilibratingor 6 daysoversaturatedotas-sium bromidesolution 81o rh at 25C)at the required emperature.Results ereexpressedsmgwaterbound100mg dry weight f corneum.The two pieces f comeurnrom eachguinea-pigwerekept togetherand eachpiecewas measured t a different emperature.n this waystatistical omparisons etween wo temperatures ould be made byanalysis f varianceusingeachanimal as a statistical lock.In two separateexperiments comparisonbetweenextensibility t4-5Cand at 18-22Cwasmade. n the second xperiment aterbindingwasmeasured n the samepieces f corneum.

RESULTS

Table showshe meanextensibilitybtainedn the two experimentstogether ith the meanvaluesor waterbinding n experiment.Analysis f variancehowedhat n bothexperimentsxtensibilityassignificantlyess t the ower emperature itha probability f thedifferencearising y chance f less han 1 o in eachexperiment.his difference c-curredalthoughhe rh washigherat the lower emperaturend extensi-bility s known o increaset higher h at constantemperature3).The measurementsf waterbindingndicated higherwatercontent tlower emperaturesnd hisdifferenceas tatisticallyignificantP < 0.05).

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242 JOURNALOF THE SOCIETYOF COSMETICCHEMISTSTable I

Extensibility nd water bindingof guinea-pigootpadcorneum t differenttemperatures

Temperature Relative Extensibility Water boundhumidity (% 100 g-X (mg 100(C) ( load) dry wOExperiment 1Experiraent 2

4.8 69 4.6 -18.9 62 6.3 -4.0 80 0.8 -

22.0 58 1.3 -4.0 86 - 26.1

22.0 81 - 20.612 replicates n experiment 1, 11 in experiment2.

This difference can be accounted for by the increase in rh oversaturatedpotassiumbromide solution with decreasingemperature 8).The decreasen extensibility t low temperature annotbe accountedorby a decrease n water content and must be due to a direct effect of tem-peratureon the corneum.DISCUSSION

The results show that at low temperaturescorneum extensibility sreduced.From these and previous esults 3, 6) it can be concluded hatextensibility f isolatedanimal corneumdepends pon both the tempera-ture and rh of the air in contact with the corneum. If this conclusion isapplied o humancorneum n vivo t can be predicted hat theseconditionswill lead o skinchapping.Gaul and Underwood's bservations5) showedthat chappingoccurredwhen the air temperaturewas low out of doorsalthough rh was high. However, at the same time rh indoors will be lowparticularly n centrally heated buildingswhere external air is warmedwithouthumidifying. uring a normalday, skinwill therefore e exposedto the two conditions, ow rh indoorsand low temperatureout of doors,which the experimentson isolated corneum indicate will lead to skinchapping.When living skin s exposedo low temperature r low rh therewill bea gradient of temperatureor water content across he corneumwith theouter ayersbeingcolderor drier than the deeper ayers.The resultwill bea lower extensibilityon the surfaceof the corneumso that when the skin sstretched r flexed he surfaceayerswill crackmore easily,while he deeper

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INFLUENCE OF TEMPERATURE AND RH ON STRATUM C:ORNEUM 243

layersremain intact. The crackingof the surface ayer is seenas flaking ofthe skin surface nd commonlyoccursn areassubjectedo flexingsuchasthe fingerwebs. n more severe ases f chapping,complete upture of thecorneumoccurswhen extensibilityof the entire comeurn s reduced o theextent where t cracksunder tension.Any external actors, suchas cold ordryingwinds,which ncreasehe gradientof temperature r water contentwill lead to a greaterdegreeof skin flaking or chapping.Factorswhichreduce he gradients, uchas clothing,will reduce lakingand chapping.(Received: 2th January1972)REFERENCES

(1) Blank, I. H. Factors which influence the water content of the stratum corneum. J. Invest.Dermatol. 18 433 (1952).(2) Singer, E. J. and Vinson, L. J. The water binding propertiesof skin. Proe. Sei. Sect. ToiletGoodsAss. 46 29 (1966).(3) Middleton, J. D. The mechanism f water binding n stratumcorncure.Brit. d. DermatoL80437 (968).(4) Wildnauer, R. H., Bothwell, J. W. and Douglass, A. B. Stratum corneum biomechanicalproperties. I. Influence of relative humidity on normal and extracted human stratumcorneum. J. Invest. DermatoL 56 72 (1971).(5) Gaul, L. E. and Underwood, G. B. Relation of dew point and barometricpressure o chap-ping of normal skin. J. Invest.Dermatol. 19 9 (1952).(6) Middleton, J. D. The effectof temperature n extensiblity f isolated orneum nd ts relationto skin chapping.Brit. J. Dermatol.81 717 (1969).(7) Middleton, J. D. The mechanism f action of surfactants n the water binding propertiesofisolatedstratum corneum.J. oe. Cosmet.Chem.20 399 (1969).(8) Acheson,D. T. in Humidityandmoisturemeasurement 521 (1965) (Reinhold, New York).