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`’cupysgm © 1974 by The Williams a Wilkins Co.
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`Vol. $2. No. 1!
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`Prmted in l-'.S.A.
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`REGIONAL DIFFERENCES [N THE THICKNESS (CELL LAYERS) OF THE HUMAN
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`STRATUM CORNEUM: AN ULTRASTRUCTURAL ANALYSIS*
`KAREN A. HOLBROOK. PH.I).. AM) GEORGE F. UDI..-‘-\ND. MD.
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`ABSTRACT
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`The importance of the stratum corneum as the rate-limiting barrier to percutaneous
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`penetration has been well documented in the literature. Data have also been reported which
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`suggest that the barrier function of this zone varies among different regions of the body.
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`However. little attention has been given to regional variation oi'two morphologic parameters
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`known to affect permeability—thickness and number of cell layers. in the present study.
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`significant regional variation in both the mean thickness and the mean number of cell layers
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`has been documented for four selected. sample regions of the body Ufa pflpulation of six adult
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`volunteers. and for two more homogeneous subgroups separated by sex and age. While the
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`pooled data from the total population and the pooled data from the male and female
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`subgroups are in general agreement. it has been shown that there is also marked individual
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`variation within a region that is characteristic and specific for each individual. The number
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`of cell layers appears to account for the variation in thickness.
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`1
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`V
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`in the permeability of
`Widespread interest
`- human skin has generated a plethora of experimen-
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`tal investigations using in vivo and in vitro tech-
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`- niques. Several of the in vivo studies were carried
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`out by measuring the diffusion of a radioactively
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`“labeled compound through the epidermis and der-
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`mis into the blood vascular system of living sub.
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`'jects [1. 2]. Other investigators have used in vitro
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`. model systems in their experimentation [3]. In the
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`latter method. permeability of human cadaver skin
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`. is measured. The measurements of the kinetics of
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`transport that are obtained from both experimen-
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`tal approaches would not be expected to differ
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`significantly on the basis that only the nonviable
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`”'cells of the stratum corneum serve as the rate-
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`_ limiting barrier to the passage of substances across
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`the epidermis [4 1.
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`The rate of diffusion of molecules is.
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`dependent upon the length of the diffusion path-
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`. way. which in this instance is the thickness ofthe
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`stratum corneum. However. data on the thickness
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`"of the stratum corneum are limited and general-
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`ized and do not systematically take into account
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`“the possibility of significant
`regional variations
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`' which might be implied from the demonstration of
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`regional variation in percutaneous absorption i1.
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`. 2].
`The studies to investigate the differences in
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`Hthickness and numbers of cell layers of the stratum
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`comeum from different regions of the body have
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`- failed to establish controls for preservation of the
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`full thickness of the samples [5, 6]. Nonetheless.
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`the importance of these two parameters of the
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`This work was supported by USPHS Grants [ME-02600.
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`AIM-08368. and (EM-16598 from the National Institutes of
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`“Health. and by a grant from the Procter and Gamble
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`Company. Cincinnati. Ohio.
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`’ From the Department of Biological Structure [KAI-l
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`and GFO). and the Department of Medicine. Division of
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`. Dermatology tGFOJ. University of Washington School of
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`Medicine. Seattle. Washington 93195.
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`5
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`stratum corneum to the interpretation of permea-
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`bility data has been recognized: "Strictly speak-
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`ing. such comparisons of [rates of permeation] are
`not valid unless one corrects for horny layer thick~
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`ness or alternatively for number of cell layers" [71.
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`It was,
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`the objective of the present
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`study to apply methods that would assure preser—
`vation of an intact. full-thickness stratum corneum
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`and to evaluate quantitatively the regional varia-
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`tion in total thickness and numbers of cell layers of
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`this epidermal zone using electron microscopy.
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`MATERlALS AND METHODS
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`i'lexor
`Specimens were obtained from the abdomen.
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`forearm. anterior thigh. and posterior inferior iliac re—
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`gion of six. healthy. human volunteer subjects.
`three
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`white males and three white females within the age group
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`of 25—31. The areas to be sampled were gently cleansed by
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`a single stroke with a 70% alcohol wipe prior to biopsy
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`with a high-speed. electric rotary drill fitted with a
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`2.5-mm biopsy punch. The tissue "plug" obtained was
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`then marked in a manner to assure the preservation of
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`full-thickness stratum corneum during further process-
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`ing. Small sheets of lens paper were placed above and
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`below the core of tissue. The "sandwiched" preparation
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`was then set onto a hollow plastic cylinder (prepared by
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`trimming away the bottom of a BEEM capsule) and
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`secured in place with an open-top cap iFig.
`Ii. The
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`assembled capsule with the paper-enclosed biopsy sam-
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`ple was carried through fixation, dehydration. and em-
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`bedment for electron microscopy. Thus. cell layers which
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`might have become detached during processing were
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`trapped beneath the lens paper and could be included in
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`the measurements of thickness and the counts of cell
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`layers
`(Figs. 2a.bl.
`In pilot assays of
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`marking the surface with AgNO, and particulate carbon
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`prior to removal of the biopsy specimen established that
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`the technique of biopsying did not remove the outer layer
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`of the stratum corneum.
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`Tissue was fixed. for electron microscopy in 2 parts of
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`'3‘“? osmium tetroxide buffered with 1 part of 0.2 M
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`s-collidine at
`low temperature for 2 hr. dehydrated
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`through a graded series of alcohols. and embedded in
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`L'OREAL USA, INC. EX. 1017
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`“31
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`L'OREAL USA, INC. EX. 1017
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`416
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`THE JOURNAL OF INVESTIGATIVE DERMATOLOGE
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`r'
`U —~ % - +
`Skin
`F.
`It“
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`biopsy
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`Lens paper
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`markers
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`Flush: nnq mm
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`open lrd
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`[he plashr
`[S]. Follnumg; pnlymrnzam-n.
`Epun '41.”
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`r'yLindi-r Wm \‘H!
`tawny having the air-sue and enclming
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`paper 11- hr urienled cm mL-Iui slum with the stratum
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`t'nrm-um :‘mFiliUflE‘d parallel In rho tum ul' the mic-mumm-
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`t'hm'k surh [hm tissue Hmflmm maulrl he cm in :I plmw
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`perpendirularIn[ht-5kmsLJrl'.‘:t1-.'I‘l1u:k sections t 1.5 pm!
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`were prepared with glass knm-s 21ml lhin sectinn». in Ihv
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`‘llu-r mlr-rl'erenre color mnur. were ml through both thr-
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`ll~4~ue and 1011: paper with :1 dmmund kniiv mounted un :1
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`Ri-u'herl
`()m {.3 lillrmrm'rnn_>mc Several
`thin :zecliuns
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`were ml at each 0! 8—41] uniformly separated intervals
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`FIlOIIOn.
`dehydrmion ‘-
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`Assembled capsule.
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`paper and biopsy
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`I.”
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`ass-urt-
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`[‘CLhmqur' ulemgnml
`[“1“
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`prvsonatmn nf full-thickness sernlum mrneum during:
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`[inner-5mm n! (Issue !ur elemrnn :nu'rusmpv.
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`I
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`LENB PAFEFI
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`,;g x‘ *1.mi
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`.../4%
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`'..‘:
`Fm,
`;min-r marker uhuu-
`131 Light mn'rngraph shnwmu the lane-
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`i
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`Imcrngruph nt human epidermth and Ion.» paper marker
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`'nurmm epidermln I
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`"3|!-
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`Ihl Eleclrun
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`'I‘I-IIC‘KNESS 0F H’I‘RATI'M CORNEUM
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`417
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`[1 was estimmed Lhzn. measurements
`each skin sample.
`'Lhruugh the entire hinpsy sperimen. All sections were
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`were made over a Inlal nl‘ 2072:”: lineal mm (if the stratum
`duuble stained with haturmed uram'l acetate and Hey,
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`ntild's 19]
`lead citrate. Sectinus were examined in a mrneum. For the purpose nI‘ex-aluming lhe thickness. :1
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`Philips 200 electrnu microscope.
`line was drawn through the straium mrueum perpenr
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`Fifty electron mierngruphs were phntngraphed from
`ciirulnr 1n the skin surface nn ear-h micrograph and
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`.1
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`la. In Stratum eorneum from the posterior inferior iliac region. Note the variation in the ihickness along the
`FIG. 3:
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`- phmugrapheci segment. in,
`.- 3.865; 11,
`-: 4.050! lel Siralum mrueum From the thigh. The thickness is measured as the
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`height of the black line and the. number of eells intersected are crammed.
`- 5,680]
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`y.
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`418
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`THE JOURNAL or INVESTIGATIVE oenmrocooi
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`'4: Mean thickness and mean numbers of cell
`FIG.
`layers of the stratum corneum for the four regions saro—
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`pied from six volunteer subjects. (Electron micrograph
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`“figment;
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`.0001. The large standard deviations '
`level of 9 ~’
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`calculated for these pooled data reflect
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`turcs‘. til that
`the stratum ('nrneunt
`in a given
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`sampled region is variable in both thickness and
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`numbers of cell layers among [he subjects studied.
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`and (2) that a sample length of stratum corneum'
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`measured from any region of each individual is not
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`consistent in thickness and numbers of cell layers.
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`(Figs. :la.b_l. The individual data from each body
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`region of each subject are expressed in Tables I
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`(abdomen). [1 {flexor forearml. Ill lthight. and l\'
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`(backl.
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`the thickness of the
`it was also found that
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`stratum corneum appears to vary proportionately
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`with the numberof cell layers comprising that zone“
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`of the epidermis. This proportionality has been
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`calculated by dividing the mean thickness of each
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`region by the mean number of cell layers for that
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`region. The resulting value also provides an averv
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`age dimenston for 1ndtudual CE” thICknESb' 1r;
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`three of the four regions the cell
`thickness was
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`determined to be .l.‘—.18 um. However. by this»
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`TABLE l
`measured from the deepest layers to the must superficial.
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`The number of cells intersected by that line were then
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`Mean. thickness (pm! and mean number of cell layers of
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`cnunted (Fig. 3c). On several micrographs more than one
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`the stratum comeum from the abdomen of six human
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`measurement was obtained when the thickness of the
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` stratum corneum showed obvious variation along its subjects
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`photographed length tFigs. fiinJil.
`Fluff-“3%:
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`The measurements were then type-d onto IBM com-
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`putt-r cards and submitted to the CDC 6400 computer for
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`statistical analyses. Mean values. standard deviations.
`
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`and p-valucs of comparisons were computed using ver-
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`sion 2.1l ot’ the SPSS Statistical Package for the Social
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`
`
`Sciences [In].
`
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`RESULTS
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`It was the primary objective of this study to
`
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`document regional variation in the thickness and
`
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`number of cell layers ot'the stratum comeurn. first
`
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`for a selected sample population and then for two.
`..
`.
`.
`.
`.
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`more homogeneous subgroups 0! Individuals Within
`that population. The criteria used to establish the
`
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`latter groups Were sex and age. The three male
`
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`subjects selected were of ages 25%? and the three
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`female SUleeClS were 30-31 years Of age. The
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`consistency of the data from each region and each
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`individual was also considered in the interpretn-
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`Lion of results.
`
`TABLE ll
`
`
`Mean thickness (umland mean number of cell layers of
`
`
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`
`
`
`
`
`the stratum. carneum from the llcxor forearm of six
`
`
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`
`
`human subjects
`
`
`
`n
`u
`‘ 0'
`'
`._1:7—.-—— ——
`..
`_
`....
`,wl if"
`
`
`.
`
`.
`
`~ 7
`
`
`Pooled Data from All Subjects
`
`
`
`
`
`Figure. 4 is a graphic representatitm of the mean
`
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`
`
`values for both thickness and numbers of cell
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`layers of the stratum corneum from the [our body
`
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`
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`regions tested. Each bar represents a composite
`
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`
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`mean value that was obtained as an average value
`
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`
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`of the individual means of the data from the six
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`subjects selected. With the mean value of the
`
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`abdominal stratum corneum serving as the stan-
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`dard for comparison. both thickness and numbers
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`of cell
`layers from the l'lexor forearm. thigh. and
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`back were compared by use of the t—test and were
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`found to be significantly different at a confidence
`
`
`
`THICKNESS 0F STRATUM cosNEt'M
`
`
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`
`
`
`
`419
`
`
`
`V '
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`method of calculation the cells of the abdomen
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`were estimated to have a greater average thickness
`
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`.22 pm. These results appear to support
`of
`a
`
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`
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`
`
`
`generalization that regional variation in the thick-
`ness ot stratum corneum is related to the number
`
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`,ot'cell layers that comprise it within a given region:
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`the data appear to lend less support to an alternate
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`. explanation of the regional differences as a conse-
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`quence of extensive variation in individual cell
`thickness. These cmtclusions. although drawn from
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`mean values computed from the. total population
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`of subjects. are borne out by the data that were
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`«summarized independently for the male and fe-
`male subgroups.
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`‘ Pooled Data from Male and Female Subgroups
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`Figure :3 graphically displays the mean values for
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`stratum corneum thickness and numbers of cell
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`layers of all female subjects. The same data are
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`illustrated for the male subjects in Figure 6.
`In
`
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`'both groups.
`the mean thickness of the stratum
`
`.4
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`.
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`
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`TABLE [It
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`
`Mean thickness turn I and mean number of cell layers of
`
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`the stratum corneum from the rhino of six human
`
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`subjects
`
`(Mnr n-
`.t
`4r.
`... .. w
`“ mm
`'
`
`.
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`.-
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`.
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`—-
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` uu
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`TfllflKmall''“ATUKCOINEIJI
`
`I‘IIV'I
`
`NIMSH
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`
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`Fin. 5'. Mean thickness and mean number of cell layers
`
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`of the stratum corneum for the four regions sampled from
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`the male subgroup. [Electron micrograph segments s.
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`6.35:?)
`
`
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`
`1133II'0"
`
`
`
`
`
`THICKNESSo!I'I'M'I'IJICOIHEU‘DI
`
`{pl}
`
`
`
`IIJAV'I1113I“‘ou
`
`“noun:
`
`rum:
`router.)-
`
`rn IGB
`
`M“
`
`ti.- Mean thickness and mean number of cell
`Ftc.
`
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`
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`
`
`
`
`layers of the stratum corneum for the four regions sam-
`
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`
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`pled from the female subgroup.
`lElectron micrograph
`
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`segments - 6.365)
`
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`
`.0001) when
`corneurn is significantly different tp <1
`
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`
`
`compared with the mean abdominal dimensions.
`The mean numbers of cell layers were also signifi-
`
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`
`
`
`cantly different [p <.
`.0001) among the four regions
`
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`of the male subjects. but did not differ significantly
`
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`
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`
`
`.154]
`[1)
`in a comparison of the abdomen and
`7
`
`
`back of female subjects. It may be noted that the
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`calculated individual cell thickness is greater for
`
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`the female subjects as a group and for each female
`
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`
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`
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`subject
`individually when Compared with the
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`
`group of males and with the individual male
`
`
`
`
`subjects. Again. male and female group data
`
`
`indicate that there are thicker cells in the abdomi-
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`
`
`nal region. The pooled data from the total popula»
`
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`tion and the data from the two subgroups are in
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`good agreement.
`
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`
`
`
`
`
`
`. I!
`
`a
`
`.
`
`
`
`'
`r4
`
`
`lib
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`
`
`
`
`
`
`TABLE l\'
`
`
`Mean thickness turn) and mean number of cell layers of
`
`
`
`
`
`
`
`
`
`
`the stratum corneum from the back ofsix human subjects
`
`
`
`
`
`
`
`
`
`
`l
`14.10 Mam -t..,..t..t..,»."gtm
`.n—t 2.,
`,.
`w_
`v
`‘
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`h
`.
`r.
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`'
`
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`
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`l
`
`
`
`
`
`
`
`
`
`
`420
`
`THE JOURNAL OF INVESTIGATIVE DERMATOLOGY
`
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`
`
`Individual Data
`
`
`
`It may be seen from Tables l—IV that there is
`
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`
`
`significant variation among individuals in both
`
`
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`
`
`thickness and numbers of cell layers of the stratum
`
`
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`
`
`corneum from the regions sampled. Having estab~
`lished the individual variation. we then considered
`
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`whether it would be possible to obtain a value for
`
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`each subject that could be used to “correct” the
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`data for individual variation and obtain theoretical
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`values for thickness and numbers-of- cell bursts that
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`would be equivalent among subjects. The mean
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`
`thickness and the mean number of cell layers from
`
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`the abdomen. fiexor forearm. thigh, and back of
`
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`
`
`each subject were averaged to obtain an overall
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`
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`“body value" for thickness and numbers of cell
`layers characteristic of each subject. These aver-
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`ages were then used to obtain a mean value for
`
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`thickness and numbers of cell layers for the group
`of subjects. Deviation from this mean was calcu-
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`lated for each subject and that value was used as a
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`factor to adjust the individual regional data. The
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`
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`results of this method to con-act
`the data only
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`
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`further emphasized and supported the conclusion
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`
`
`of specific individual variation in a region among
`
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`the subjects of a. population.
`
`
`
`
`DISCUSSION
`
`
`This study is the only work to date in which
`
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`
`
`
`measurements of the thickness and numbers of cell
`
`
`
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`
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`
`
`
`
`
`layers of the stratum corneum are compared from
`
`
`several body regions of the same subject. Blair [5]
`
`
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`has reported the mean number of horny cell layers
`
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`and mean horny cell thickness characteristic of the
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`interscapuler region and the extensor forearm. but
`
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`the biopsies studied from these into regions appear
`
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`
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`to have been obtained from different subjects. The
`
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`author’s primary concern was to adopt and elabo-
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`rate a method to enhance visualization of horny
`
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`cell layers and not to-compare the stratum corneum
`
`from the two regibns Baker and Kligm‘an [7]
`
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`
`
`acknowledged regional variation in the stratum
`
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`
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`cornsum thickness and/or numbers of cell layers.
`but they used this information only to advocate
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`
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`care in interpretation of permeability data.
`In
`
`
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`
`
`
`
`another study in which functional differences in
`
`
`
`
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`
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`the stratum corneum were compared. Smith.
`
`
`
`
`
`
`Fischer, and Blank ill] compared the numbers of
`
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`
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`layers of cells from the abdominal and scrotal
`
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`stratum corneum by repeatedly stripping this
`
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`
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`layer. Rushmer and co-workers
`reported
`[12]
`
`
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`
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`their findings on the total skin (epidermis plus
`dermis) thickness of the scalp.
`forehead, back.
`
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`
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`
`
`
`abdominal, thigh. wrist. and palmar surfaces and
`included light microscopic measurements of the
`
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`
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`stratum corneum from the flexor forearm. sole.
`
`
`
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`
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`scrotum. and callus.
`
`
`
`
`It is therefore apparent that while many authors
`
`
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`
`
`have reported values of thickness and numbers of
`
`
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`
`
`cell layers or the stratum corneum. their results
`
`
`
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`
`
`
`
`
`
`
`
`
`
`
`have been obtained by diverse methodology. Some
`of the techniques which have been used to estimate
`
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`both of these parameters include: (1) scotch tape
`
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`
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`stripping to remove the cell layers: the numbers of
`
`
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`
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`strippings were correlated with the numbers of cell
`layers [13];
`(2] treatment of paraffin-embedded-
`
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`and frozen biopsies with alkali to cause swelling.
`hence better visualization and more accurate .
`
`
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`
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`counting of the horny cell layers [14]; (3} applica-
`
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`
`
`
`tion of standard chemical fixation. paraffin em-
`
`
`
`
`
`
`bedment. and staining procedures for histologic
`sections: thickness was measured with a microme-
`
`
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`
`
`
`ter eyepiece [15]; i4) mechanical measurement of
`
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`dried tisme by means of a modified Starett gauge
`
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`
`
`IS]: and (5') preparation of tissue by chemical_
`
`fixation and plastic embedrnent for electron mi-
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`
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`croscopy: measurements were made from electron .
`
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`
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`micrograp'hs [16]. No techniques have been de-
`scribed in any of these studies to insure full
`
`
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`
`
`
`
`thickness preservation of stratum corneum.
`
`
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`
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`
`
`
`
`r
`
`General Body Thickness of Human Stratum
`
`
`
`
`
`Comm
`
`The thickness of the stratum corneum has been .
`
`
`
`
`
`
`
`
`
`too frequently expressed in a single value
`all
`
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`
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`intended to be representative of the body as a'
`
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`
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`whole. These figures are probably not a true
`
`
`
`
`
`
`average calculated from several body regions. but
`
`
`
`
`
`
`
`
`rather were based on on isolated measurement.
`
`
`
`Values of [3.2 pm [17]. H um [18]. and 15 pm [191‘
`
`
`
`
`
`have been reported as an average thickness of dry
`
`
`
`
`
`
`
`
`
`
`stratum corneum. By comparison. our “body aver-
`
`
`
`
`
`
`ages" calculated as the average value of the mean
`
`
`
`
`
`
`
`
`
`thicknesses of the four regions ranged from Bil—12.9
`
`
`
`
`
`
`
`
`
`
`1.1m. Only the flexor forearm. and in one case the
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`thigh. had a mean thickness within the range
`
`assumed as an average for the whole body by other
`
`
`
`
`
`
`
`
`
`authors.
`
`
`Again. without reference to regional variation. '
`
`
`
`
`
`
`
`
`
`
`
`
`
`the stratum comeum has been discussed as ap-
`
`
`
`
`
`
`
`
`proximately 15 cell
`layers thick except
`for the
`
`
`
`
`
`
`
`
`
`palm. sole. scrotum. hand. and foot
`[1-11 or has
`
`
`
`
`
`
`
`
`
`been described in ranges of 10-223 cell layers [20]
`
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`
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`and 15—30 cell layers with 20—22 most frequently
`
`
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`
`
`
`
`
`counted [21]. In this parameter, our data for the
`
`
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`
`
`
`
`
`mean numbers of cell
`layers of the. four regions”
`
`
`
`
`
`
`
`
`
`
`sampled lie within a more narrow range of 14—23311
`
`
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`
`
`
`
`cells. Only one enceptional measurement. from the ‘
`
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`flexor forearm. of 30 cells was counted. “Body
`
`
`
`
`
`
`
`
`averages" for the numbers of cell layers compared
`
`
`
`
`
`
`favorably (15.6—22.8) with the range expressed
`from the individual data.
`
`
`
`
`
`
`
`
`Regional Variation in the Stratum Corneum
`
`
`
`
`
`
`It has been commonly recognized but poorly
`
`
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`
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`documented that the thickness of the epidermis as
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`a whole [15. 12] and ot‘ the stratum corneum
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`portion of the epidermis specifically. vary in thick-
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`ness and numbers of cell layers in different regions
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`of the body. We have selected four regions of thou
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`body in document
`this variation. The data ob-
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`tained in this study and the measurements which
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`have been reported in the literature for the same
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`regions are compared in Table V.
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`Comparison of measurements of thickness and numbers of cell layers reported in the literature and measurements
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`obtained in the present study
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`“m“ if FT
`1”
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`Abdomen
`13 um
`Scheuplein [18]
`V5725
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`Blank ti: Scheupiein [2T]
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`18
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`‘ 18 mean
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`* iii—20.9 range
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`10.2-23.4
`25
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`“21.6 mean
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`‘16.7—l30 range
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`No reported
`measurements
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`‘193 mean
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`'14.:1-‘22.‘l range
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`9.64011
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`14—28
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`19 mean
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`Brody [16]
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`Smith. Fischer. 8; Blank
`l11 l
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`Blair [5]
`Odland [28]
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`Blair [5] {measurements
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`obtained from interscap-
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`ular region]
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`Anderson 8: Cassidy [5]
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`(measurements obtained
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`from "hip")
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`‘15)} mean
`“3.4 pm mean
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`*8.2—11.3 range
`*14-21J range
`1
`“‘ Measurements obtained in the present study.
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`THICKNESS DF STRATUM CDRNEUM
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`421
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`TABLE V
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`‘ Flexor
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`forearm
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`Thigh
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`"
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`I Back
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`40 pm
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`'82 am mean
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`‘fi.9—9.8 range
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`15 pm
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`‘12.!) um mean
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`’8.l—.l6.2.um range
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`8.57 13.8 um
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`'10.B um mean
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`*7 .77 15.3 range
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`['2 pm
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`6.2s19.l
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`11.8 mean
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`Rushmer e1 al [12]
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`Humphries & Wildnauer
`['26] (measurements
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`obtained on "leg"!
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`Humphries 8: Wildnauer
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`['26]
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`Anderson & Cassidy [6]
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`(measurements obtained
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`from “hip"i
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`I
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`Number of cell layers. in the majority of exam—
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`ples. our measurements for the number of cell
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`layers comprising the stratum corneum in a given
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`region compare favorably with the values reported
`in the literature. In those instances where there are
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`discrepancies. we may account for the differences
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`by the failure of others to control the preservation
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`of all layers in tissue processing.
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`Thickness. There is considerably more variance
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`between our measurements of thickness and those
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`reported in the literature. Again, methods ol'tissue
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`preservation may explain these discrepancies. The
`amount 01' water allowed to remain in the tissue
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`during processing can account for significant alter—
`ation in this measurement. The stratum corneum
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`can increase its thickness severalfold when fully
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`‘ hydrated.
`Idson [22] has reported that. a dry
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`stratum corneum of 15 ,um thickness can expand to
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`48 pm when fully hydrated. It is. in fact. possible
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`that processing of horny layer for microscopic
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`analysis alters the thickness significantly.
`A further consideration when comparing the
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`thickness and numbers of cell layers from several
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`4 studies is the precise location ot'snmpling. Identifi-
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`cation oi' the region investigated is usually limited
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`to a general term such as back. abdomen, or thigh.
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`Can we compare our “back" measurements from
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`the posterior and inferior
`iliac region with less
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`specifically indicated "hack" measurements of
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`other investigators? One might expect there to be
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`significant regional variation within any broadly
`identified region.
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`The Relationship of Age and Sex to the Thickness
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`and Numbers of Cell Layers of
`the Stratum
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`Corneum
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`The importance of age and sex as variables in
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`determining the thickness and numbers of cell
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`layers of the stratum corneum has been given
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`varying degrees of empha:
`me literature. Both
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`cases have been supported with data. A review of
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`the early literature illustrates this controversy [15]
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`which appears to be still unresolved. More re-
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`cently. Black [‘23] has determined the entire skin
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`thickness to decrease after 65 years of age. but to
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`do so without any relationship to sex. Maximum
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`thickness has been lbund in individuals of 35 years
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`of age [24]. Plewig [25] recognized larger cells in
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`the stratum corneum of females in all areas investi-
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`gated. By contrast. Humphries and Wildnauer [26]
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`concluded that there is “no apparent correlation
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`between the variation in sample thickness. age. or
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`sex of the individual."
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`The mean values of thickness and cell numbers
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`obtained for male and female subgroups are not
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`significantly nor consistently greater for either
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`422
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`THE JOURNAL OF {NVESTIGATNE DERMATGEDGY
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`group. Our data cannot support a relationship of
`age and sex to the overall thickness and numbers of
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`cell layers of the stratum c'orneurn. but the calcu-
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`lated thicknesses of individual horny cells in all
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`cases are in accord with a larger cell size for all
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`regions of females as reported by Plewig [25].
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`Relationship of Thickness [Nam ber of Cell Layers)
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`of the Stratum Comeum to Permeability
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`Two investigations that have been designed to
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`explore the kinetics of permeability in several
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`anatomical regions of the body were carried out in
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`vivo by Feldma'nn and Maibacb Iljand Maibach et
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`al [2]. By measuring the amount of “C present in
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`the urine after application of “Ghydrocortisone to.
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`a given site.
`it. was determined that the rate of
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`absorption of that compound through the skin of
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`the back is 1.7 times more rapid than the rate of
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`absorption through the flexor forearm [1 ]. Penetra-
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`tion of parathion and malathion is 2.1 times and
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`1.4 times greater through the abdominal skin when
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`compared with the flexor forearm [2 ]. Both studies
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`suggest that the skin of the flexor forearm is a more
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`resistant barrier than the skin of either the abdo-
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`men or back. The thickness and cell layer measure-
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`me