Contact Dermatitis, 1999, 41, 264–267 Copyright C Munksgaard 1999Printed in Denmark . All rights reserved

ISSN 0105-1873

The influence of patch test size and design onthe distribution of erythema induced by

sodium lauryl sulfateM N C M. W

Department of Dermatology, Amersham Hospital, Whielden Street, Amersham,Bucks HP7 0JD, UK

Patch testing is an invaluable tool for the experimental induction of acute irritant contact derma-titis (ICD), with a variety of chamber systems available for use. Ideally, the inflammatory reactionsproduced should be of uniform intensity across the test area, thereby facilitating grading of theresponse and tissue sampling for histopathological studies. Unfortunately, annular, follicular and/or blotchy erythema frequently occur. In this study, we set out to compare the performance of 5patch test systems (8 mm, 12 mm and 18 mm Finn Chambers; 19 mm and 25 mm Hilltopchambers) when testing normal healthy volunteers with sodium lauryl sulfate at concentrationsselected to produce mild, moderate and moderately severe reactions. Visual assessment of the patchtest sites revealed good dose responses with all 5 chamber types. Uniformity of erythema acrossthe test site was more closely linked to the actual intensity of response than the delivery systemitself, mild reactions being far less likely to display homogeneous erythema than moderately severereactions. Extra large chambers did not perform significantly better than smaller chambers. Bal-ancing the need for a uniform reaction pattern and adequate tissue sampling area, against theexposure risk, we conclude that 12 mm Finn Chambers represent the optimum patch test systemfor acute SLS-induced irritation where histopathological investigations are the ultimate aim.

Key words: irritant contact dermatitis; sodium lauryl sulfate; Finn Chamber; Hilltop chamber.C Munksgaard, 1999.

Accepted for publication 24 May 1999

Patch testing has long been used as a tool to exper-imentally reproduce cutaneous irritation in orderto study the clinical features and pathogenesis ofirritant contact dermatitis (ICD) (1, 2). One prob-lem associated with this technique, which is be-lieved to be particularly acute when standard 8mm Finn Chambers are employed, is that reactionpatterns can be non-uniform across the test area.Annular, follicular and blotchy reactions may allbe seen in the responses to many irritants, includ-ing the most widely utilized experimental irritantof all, sodium lauryl sulfate (SLS). This can makethe intensity of the patch test response difficult toassess, both semi-quantitatively using visual scor-ing, and quantitatively with bio-engineering tech-nology. It can also make interpretation of histo-logical data from biopsied patch test sites problem-atic at times.

It has been suggested that the use of extra largeFinn Chambers and alternatives to the Finn

Chamber, such as the Hilltop chamber, may givebetter results when testing irritants, particularlywith respect to the rate of false-negative reactions(3). Whether they also produce more uniform reac-tion patterns is rarely commented upon. Since it isimportant to this group, in terms of ongoing im-munopathological studies, to achieve as homogene-ous a reaction pattern as possible, we set out to sys-tematically compare the performance of 5 differentpatch test systems, when patch testing with SLS.

Materials and Methods

Subjects15 healthy female volunteers, with no past or pres-ent history of skin disease (age range 26–50 years,mean 36.6 years), took part in the study, after pro-viding written informed consent. Approval for thestudy was given by the Wycombe Local ResearchEthics Committee.

265PATCH TESTING WITH SLS

Patch tests

Sodium lauryl sulfate (±99% purity; Sigma-Ald-rich Ltd, Gillingham, Dorset, UK), freshly pre-pared in distilled water, was chosen as the experi-mental irritant.

Table 1 gives the comparative patch test infor-mation in detail. 3 different concentrations wereused with each chamber type. These concen-trations were determined in an initial pilot studyso as to produce, as far as possible, mild, moderateand moderately severe reactions in the majority ofthose tested. The volumes placed in each chamberwere those recommended and routinely utilized byother investigators (4,5; Basketter, personal com-munication).

All volunteers received each of the 5 chambertypes containing SLS prepared at the 3 concen-trations, i.e. a total of 15 patches. These were ap-plied to the upper and lower back in a randomizedfashion for 23 h, after which time they were care-fully removed.

Visual assessments of the intensity of erythemawere made 1 h later using a scale of 0–4π, where0Ωno erythema, 4πΩsevere erythema. The distri-bution of erythema was recorded as homogeneous,annular (peripheral ring of erythema, with littleerythema within the annulus) or blotchy/follicular(isolated, irregularly located, areas of erythema).The two authors scored the reactions indepen-dently in the first instance. Good concordance inthe assessments was achieved.

Statistical analysis of the results was not con-sidered appropriate because of the qualitative na-ture of the information derived.

Results

All 5 chamber types gave good dose responses.Fig. 1 shows the mean visual erythema scores (π

Table 1. Details of the 5 patch test systems employed

Concentrations ofChamber type and size SLS (w/v) Volume used

8 mm Finn Chamber onScanporA* 1%, 2%, 4% 15 ml12 mm Finn Chamberon ScanporA* 0.5%, 1%, 2% 50 ml18 mm Finn Chamberon ScanporA* 0.125%, 0.25%, 0.5% 200 ml19 mm Hilltop chamberon DuraporeA† 0.25%, 0.5%, 1% 100 ml25 mm Hilltop chamberon Micropore† 0.125%, 0.25%, 0.5% 200 ml

*Epitest Ltd. Oy Finland – Finn Chambers used with filterpaper discs.

† Hilltop Research Inc., Ohio, USA – chambers contain WebrilA

pads.

Fig. 1. Mean visual erythema scores (π SD) for the variouschambers employed for patch testing with SLS. 3 concen-trations were selected for each chamber type, so as to producemild, moderate and moderately severe reactions after 23 h ap-plication.

standard deviations) for each chamber and SLSconcentration. Comparable reaction intensitieswere achieved with the highest concentrations, butthere were variations at the lower concentrations,most notably with the 8 mm Finn Chambers,which produced more intense reactions at the low-est concentration. The results for erythema distri-bution are given in Fig. 2. Examples of typical ho-mogeneous, annular and blotchy reactions seen inthis study are given in Fig. 3.

Lowest concentrations

For most chamber types, the frequency of blotchy/annular reactions was greatest at the lowest con-centration (Fig. 2A). The larger chambers gave thegreatest number of annular/blotchy reactions.

Mid concentrations

The 19 mm and 25 mm Hilltop chambers pro-duced no annular reactions at the mid concen-trations, but there were a significant number ofblotchy reactions (Fig. 2B).

Highest concentrations

For all chamber types, the frequency of homogen-ous reactions was high (Fig. 2C). The 19 mm Hill-top gave uniform erythema in all individuals.

Discussion

This study set out with a simple objective, to studythe distribution of the erythema induced by SLS

266 NICHOLSON & WILLIS

Fig. 2 (A–C). Erythema distribution at the 3 concentrationlevels chosen for each chamber type so as to produce mild,moderate and moderately severe reactions.

when applied to the skin under different patch testconditions, the ultimate goal being that of achiev-ing as uniform an inflammatory reaction as poss-ible. Uniformity is of particular value to investi-gators where accuracy of grading is important,and where representative tissue sampling for histo-logical appraisal of patch test sites is required.

Fig. 3 (A–C). Representative examples of the patterns of ery-thema distribution produced by patch testing with SLS. In (A),an annular reaction has been produced by patch testing with a19 mm Hilltop chamber at an SLS concentration of 0.25%. (B)shows a blotchy reaction from 0.25% SLS applied in a 25 mmHilltop chamber. In (C), the desired homogeneous reaction pat-tern has been induced, in this case, by the application of 0.5%SLS in an 18 mm Finn Chamber.

When designing the study, we chose to evaluateerythema only, which is, of course, only 1 compo-nent of an irritant response. However, it is argu-ably the most conspicuous, and the one uponwhich most visual scoring systems for irritancy arebased. We decided against the utilization of bi-ometry, on the grounds that, in the main, the in-

267PATCH TESTING WITH SLS

struments available are designed to sample a broadarea of the patch test area simultaneously, andwould not necessarily reflect inconsistencies acrossthe site. In addition, we purposefully induced 3 dif-ferent categories of reaction intensity, mild, moder-ate and moderately severe, so as examine the in-fluence which this parameter may have on ery-thema distribution. In accordance with theliterature in this area (6, 7), we needed to reducethe concentrations of SLS as the dose of SLS in-creased, so as to reach comparable levels of in-flammatory response across the different chambertypes.

As the results show, all of the chambers gavegood dose responses. However, none of them in-duced uniform erythema with a high degree of fre-quency across all of the reaction intensities. Al-though only assessed qualitatively, homogeneity oferythema was more closely linked to the actual in-tensity of response, than the delivery system itself.Hence, mild reactions were far less likely to displayuniform erythema than moderately severe reac-tions. This is perhaps not surprising in the contextof irritant reactions, where inflammatory mediatorrelease is likely to be localized to areas of cellulardamage.

Contrary to what we had expected, 8 mm FinnChambers produced a higher frequency of uniformreactions than the other chambers. However, thismay largely be explained by the higher intensitiesof response induced at the lowest concentration,despite our best attempts to achieve comparabilitywith the other 4 chambers. On the whole, Hilltopchambers did not perform significantly better thanFinn Chambers, nor did extra large chambers givebetter results than more moderately sizedchambers. Taking into consideration the principleobjectives of ICD induction, in our case with aparticular emphasis on the supply of suitable bi-opsy material, and weighing these against possiblerisks to the volunteer in the event of unexpectedly

severe reactions, it is the opinion of the investi-gators that the 12 mm Finn Chamber is the mostsuitable chamber for histopathological studiesusing SLS. Whether it is the optimum chamber forall irritants and for all experimental purposes re-mains to be determined.

Acknowledgements

The authors thank all the volunteers who partici-pated in the study, and Helen Duckworth for ex-pert nursing assistance. This work was supportedby the Erasmus Wilson Dermatological ResearchFund.

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Arch fur Dermatologie und Syphilis (Berlin) 1896: 34: 103.2. Pirila V. Chamber test versus patch test for epicutaneous

testing. Contact Dermatitis 1975: 1: 48–52.3. Frosch P J, Kligman A. The Duhring chamber. An im-

proved technique for epicutaneous testing of irritant andallergic reactions. Contact Dermatitis 1979: 5: 73–81.

4. Agner T, Serup J. Individual and instrumental variationsin irritant patch test reactions. Clin Exp Derm 1990: 15:29–33.

5. Tupker R A, Willis C M, Berardesca E et al. Guidelines onsodium lauryl sulfate (SLS) exposure tests. Contact Derma-titis 1997: 37: 53–69.

6. Dykes P J, Hill S, Marks R. The effect of area of appli-cation on the intensity of response to a cutaneous irritant.Br J Dermatol 1991: 125: 330–334.

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Address:

Carolyn WillisDepartment of DermatologyAmersham HospitalWhielden StreetAmershamBucks HP7 0JDUK