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Sodium lauryl sulfate irritant patch tests. II. Variations of test responses among subjects and comparison to variations of allergic responses elicited by Toxicodendron extract
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Sodium lauryl sulfate irritant patch tests. II. Variations of test responses among subjects and comparison to variations of allergic responses elicited by Toxicodendron extract Mark V. Dahl, M . D . , * Franklin Pass, M . D . , * and Ronald J. Trancik, P h . D . * *
Minneapolis and St. Paul, M N Inflammation was induced on the forearms of volunteers by twenty-four closed patch tests to either the irritant 10% sodium lauryl sulfate (SLS) or Toxicodendron extract. Each chemical was tested at eight sites on the ventral forearms of each volunteer in order to assess the variability of response among test sites in individual subjects. Inflammation was assessed about 10 minutes after patch tests were removed. The degree of inflammation elicited by both Toxicodendron and SLS was variable among subjects, but variation among individual test sites was much more marked in subjects tested with SLS (p < 0.002). The marked variability of responses to irritation that occur in any single subject may explain why irritant patch test responses do not reliably identify the irritation-prone individual. (J AM ACAD DERMATOL 11:474-477, 1984.)
The response of skin to contact with irritating chemicals is unpredictable. In the clinical setting, elicitation of dermatitis depends on body site, nature of chemical, concentration of chemical, duration of contact, regularity o f contact, environmental factors, and many other variables. Similarly, variability is c o m m o n in the clinical patch test. Irritant responses are elicited in some individuals but not in others, or at one time in a given individual but not at another.1 Recently we applied eight replicate patch tests of either 10% sodium lauryl sulfate (SLS) or Toxicodendron antigen (pentadecylcatechol) to the skin of volunteers. T h e degree o f inflammation
From the Department of Dermatology,* University of Minnesota Medical School, Minneapolis, and the Clinical Research Department,** Riker Laboratories Inc., St. Paul. Accepted for publication March 7, 1984. Reprint requests to: Dr. Mark V. DaM, Box 98 Mayo, University of Minnesota Medical School, Minneapolis, MN 55455.
474
from the irritant SLS was much more variable than from the allergen Toxicodendron. METHODS Closed patch tests with SLS or an extract o f Toxicodendron radicans (Hollister-Stier Laboratories, Spokane, WA) were applied to the forearms of volunteers after written informed consent was obtained. The population tested with SLS consisted of five male and five female subjects who had fair or average complexion and were between the ages of 18 and 34 years. T h e population tested with Toxicodendron consisted o f seven other male and three other female subjects who had fair or average complexion and were between the ages of 22 and 40 years. These latter subjects all had a history of Toxicodendron dermatitis and had previously reacted to a screening patch test with Toxicodendron antigen. Four patch tests were applied to each arm (ventrolateral surface of the mid forearm) using Al-test patches in strips occluded with Blenderm tape. The distance between test sites was 22 ram. Each patch
Volume 11 Number 3 September, 1984
Sodium lauIyl sulfate irritant patch tests. H
475
T a b l e I, Degree o f reaction at various sites at 24 hours
Subject No.
Sodium lauryl sulfate solution, 10%* 1 1 2 1 2 0 0 0 3 3 4 1 4 4 1 1 5 -+ 0 + 6 3 3 2 7 -+ + 1 8 4 3 5 9 4 3 2 10 1 1 1 Toxicodendron extract]" 1 2 2 2 2 3 3 3 3 4 4 4 4 3 3 3 5 3 2 3 6 3 3 3 7 2 2 2 8 4 4 4 9 3 3 3 10 2 2 2
Mean
S.D.
2 0 3 -+ + 3 1 3 4 1
1 0 3 1 3 1 4 4 2
2 0 4 + 1 3 1 4 4 1
1 0 4 0 1 3 ± 4 4 1
2 0 4 + 1 3 1 5 4 1
1.50 0.00 3.25 1.00 0.69 2.88 0.81 4.00 3.63 1.13
0.53 0.00 1.04 1.25 0.37 0.35 0.26 0.76 0.74 0.35
2 3 4 3 2 3 2 4 3 2
2 3 4 3 3 3 2 4 3 2
2 3 4 4 2 3 2 4 3 2
2 3 4 3 3 3 2 4 3 2
2 3 4 3 3 3 2 4 3 2
2.00 3.00 4.00 3.13 2.63 3.00 2.00 4.00 3.00 2.00
0.00 0.00 0.00 0.35 0.52 0.00 0.00 0.00 0.00 0.00
*Mean, 1.89; S.D., 1.41. tMean, 2.88; S.D., 0.75.
consisted of either 25/xl of 10% aqueous SLS or 5/M of 2% Toxicodendron oleoresin in ethyl alcohol. After 24 hours, patches were removed. The degree of inflammation was graded 5-10 minutes later and then 2, 24, and 48 hours later with an eight-point grading scale, as follows: 0 = No visible reaction __+= Barely perceptible erythema l = Mild erythema 2 = Moderate erythema 3 --= Intense erythema 4 = Intense erythema with edema 5 = Intense erythema with edema and vesiculation 6 = Intense erythema with edema and vesicular erosion RESULTS
T h e degree o f inflammation at each site is pres e n t e d in Table I. Sites 1, 3, 5, and 7 were on the right f o r e a r m , and sites 2, 4, 6, and 8 were on the left f o r e a r m . Sites 1 and 2 were nearest the elbow, and sites 7 and 8 were nearest the wrist. T h e degree o f variation among test sites was
considerably greater at sites elicited with SLS than those elicited with Toxicodendron. The total number of scores different f r o m the m e d i a n score for each subject is 27 for SLS in comparison to 4 for Toxicodendron. If the range of scores for each subject in grading point scale units is determined and summated, the total is 18 for SLS and 2 for Toxicodendron. The greater variability of scores within subjects tested with SLS, in c o m p a r i s o n to those tested with Toxieodendron, was statistically significant (Wilcoxon's r a n k - s u m test, two sided) at 24 hours (p = 0.0016). Not only was there considerable site-to-site variation in intensity of reaction f r o m SLS, but there was a considerable difference in mean reactivity among subjects in the two groups. All subjects elicited with Toxicodendron extract had mean scores between 2 and 4, whereas those elicited with SLS had mean scores ranging f r o m 0 to 4. Standard deviations for the eight tests in each subject are included in Table I, The m e a n standard
476
Journal of the American Academy of Dermatology
Dahl et al
deviation for SLS was 1.41, whereas the mean for Toxicodendron was 0.75. Corresponding sites on the left and right side scored identically 90% of the time with Toxicodendron but only 53% of the time with SLS. A similar variability was noted 2, 24, and 48 hours later. DISCUSSION The threshold of irritancy to chemicals varies considerably from subject to subject. 2,a This variation may be marked. 4''~'* Both Toxicodendron and SLS induce a wide range of reactions among subjects both in threshold and degree of reaction. In some individuals the reaction is mild, whereas in others it is severe. The variability is more marked with the irritant SLS than with the allergen Toxicodendron extract. The variation is probably relevant to clinical disease as well, since the skin of some individuals seems more susceptible to damage with irritating chemicals. The nature of protective and susceptibility factors is largely unknown, but evidence suggests that the causes of variability are multifactorial. ~ Not only did reactions to irritants differ from subject to subject, but they also differed from site to site in individual subjects. Whereas all test reactions with Toxicodendron seemed similar in a given subject, the inflammation at SLS sites varied greatly. This reaction was obvious when the arms were inspected, even at a distance. Rietschel* compared the forearm response to patch tests with aqueous solutions at 5% SLS. He also found unpredictable variability between sites, and the reasons for this variability are not apparent in his study either. According to two groups of investigators, the intensity of reaction to one irritant does not reliably predict the intensity of reaction to another. 7'~ Similarly, the intensity of reaction to SLS patch tests cannot be used as a "hyperirritability marker" for the excited skin syndrome? Since there is marked site-to-site variability in the degree of inflammation elicited by closed patch tests with SLS in a given subject, these vagaries of single test responses make comparisons between subjects or irritants un*Rietschel RL: Advances and pitfalls in in'itant and alIergic testing. J Soc Cosmetic Chem 33:309-313, 1982.
reliable. Comparative studies of irritant responses would require testing technics that minimize this variability or, alternatively, multiple tests with the same chemical to determine an average response. The wide range of reaction to irritation by SLS in a given subject at various sites underscores the apparent futility of identifying potential employees susceptible to occupational hand eczema by applying patch tests with irritants. This variability also confounds studies of therapeutic agents used to treat irritant dermatitis elicited by controlled insult. Frosch and Kligman TM have developed a chamber assay in an attempt to obtain more reproducible results. At the same time the response of a given individual's skin to the allergen in the Toxicodendron extract is relatively constant. If this is also true for other allergens, then quantitative patch test studies of allergic contact dermatitis are more likely to be valid than those of irritants. Our testing was done only at one concentration and only on the skin of the forearms. Site-to-site variations over the b o d y surface and dose response variations were not examined. The consistency of response confirms the notion that allergic contact dermatitis elicited by quantitative patch tests could serve as a model for evaluation of therapeutic agents. 4 However, often the dermatitis is so severe that inflammation is not notably suppressed, except for potent agents .4 In summary, 24-hour closed patch tests with the irritant SLS induce inflammation, but the degree of inflammation is unpredictable for site-to-site comparison in the same anatomic area (forearm). The variation is less with allergic contact dermatitis elicited by twenty-four closed patch tests with Toxicodendron extract. Although our method may be satisfactory for quantitative patch testing with strong allergens such as Toxicodendron, our study supports the observations of others that these same methods are not satisfactory for quantitative patch tests for irritants, unless the sources of variability can be identified and controlled. REFERENCES
1. MagnussenB, Hersle K: Patch test methods. II. Regional variations of patch test responses. Acta Derm Venereol (Stockh) 45:251-261, 1966. 2. Dahl MV, Trancik RJ: Sodium lauryl sulfate irritant patch tests: Degree of inflammation at various times. Contact Dermatitis 3:263-266, 1977.
Volume 11 Number 3 September, 1984
Sodium lauryl sulfate irritant patch tests. II
3. Bruynzeel DP, van Ketel WG, Scheper RJ, et al: Delayed time course of irritation by sodium lauryl sulfate: Observations on threshold reactions. Contact Dermatitis 8:236-239, 1982. 4. Kaidhey KH, Kligman AM: AssaY of topical corticosteroid. Arch Dermatol 112:808-810, 1976. 5. Skog 13, Forsbeck M: Comparison between 24-48 hour exposure time in patch testing. Contact Dermatitis 4:362-364, 1978. 6. Mathias CGT, Maibach HI: Dermatotoxicology. Monograph I. Cutaneous irritation: Factors influencing the response to irritants. Clin Toxieol 13:333-346, 1978.
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7. Czerwinska-Dihm I, Rudzki E: Skin reactions to primary irritants. Contact Dermatitis 7:315-319, 1981. 8. Bjornberg A: Skin reactions to primary irritants in patients with hand eczema. G6teberg, I968, Oscar Isacsons Trycked AB. 9. Bruynzeel DP, van Ketel WG, yon Blomberg-van der Flier M, Scheper P,J: Angry back or the excited skin syndrome: A prospective study. J AM ACADDERI~IATOL 8:392-397, 1983. 10. Frosh PJ, Kligman AM: The Duhring chamber: An improved technique for epicutaneous testing of irritant and allergic reactions. Contact Dermatitis 5:73-81, 1979.
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Sodium lauryl sulfate irritant patch tests. III. Evaporation of aqueous vehicle influences inflammatory response M a r k V. Dahl, M . D . , and Mary Jane Roering, B.S.N~
Minneapolis, MN Patch tests with aqueous solutions of the irritating detergent sodium lauryl sulfate (SLS) elicit varying degrees of inflammation from subject to subject and from site to site, For an investigation of the causes of this variability, two patch tests with 10% aqueous solutions of SLS were applied to adjacent areas o f ventral forearm skin of eighteen volunteers. In one test the water vehicle was allowed to evaporate from the patch test unit before the patches were applied. After 22 hours the patch tests were removed, and 2 hours later the degree of inflammation was graded. Less inflammation was present at the site of the dry patch test in fifteen of eighteen subjects, and the score of inflammation between each pair was significantly less at the dry patch test site (p < 0.001). These studies show that evaportion of water from aqueous solutions can influence the irritating potential of SLS on human skin. (J AM A c a o DERMATOL 11:477-479, 1984.)
A t v a r i o u s times and for various reasons, inv e s t i g a t o r s h a v e applied irritating chemicals to the s k i n o f h u m a n subjects and produced inflammat i o n . T h e d e g r e e o f inflammation elicited from
such tests is highly variable. This variability occurs not only from subject to subject but also from patch test to patch test in individual patients.1-'~'*'t S o m e causes o f this variability h a v e
From the Department of Dermatology, Universityof MinnesotaMedical School. Accepted for publication March 7, 1984. Reprint requests to: Dr. Mark V. Dahl, Box 98 Mayo, Universityof Minnesota Medical School. Minneapolis, MN 55455.
*RietschelRL: Advancesand pitfalls in irritant and allergen testing. ] Soc Cosmet Chem 33:309-313, 1982. 'l'BrownVKH: A comparisonof predictive irritation tests with suffactants on human and animal skin. J Soe Cosmet Chern 22:411-420, 1971. 477
I I
II
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Sodium lauryl sulfate irritant patch tests. II. Variations of test responses among subjects and comparison to variations of allergic responses elicited by Toxicodendron extract Mark V. Dahl, M . D . , * Franklin Pass, M . D . , * and Ronald J. Trancik, P h . D . * *
Minneapolis and St. Paul, M N Inflammation was induced on the forearms of volunteers by twenty-four closed patch tests to either the irritant 10% sodium lauryl sulfate (SLS) or Toxicodendron extract. Each chemical was tested at eight sites on the ventral forearms of each volunteer in order to assess the variability of response among test sites in individual subjects. Inflammation was assessed about 10 minutes after patch tests were removed. The degree of inflammation elicited by both Toxicodendron and SLS was variable among subjects, but variation among individual test sites was much more marked in subjects tested with SLS (p < 0.002). The marked variability of responses to irritation that occur in any single subject may explain why irritant patch test responses do not reliably identify the irritation-prone individual. (J AM ACAD DERMATOL 11:474-477, 1984.)
The response of skin to contact with irritating chemicals is unpredictable. In the clinical setting, elicitation of dermatitis depends on body site, nature of chemical, concentration of chemical, duration of contact, regularity o f contact, environmental factors, and many other variables. Similarly, variability is c o m m o n in the clinical patch test. Irritant responses are elicited in some individuals but not in others, or at one time in a given individual but not at another.1 Recently we applied eight replicate patch tests of either 10% sodium lauryl sulfate (SLS) or Toxicodendron antigen (pentadecylcatechol) to the skin of volunteers. T h e degree o f inflammation
From the Department of Dermatology,* University of Minnesota Medical School, Minneapolis, and the Clinical Research Department,** Riker Laboratories Inc., St. Paul. Accepted for publication March 7, 1984. Reprint requests to: Dr. Mark V. DaM, Box 98 Mayo, University of Minnesota Medical School, Minneapolis, MN 55455.
474
from the irritant SLS was much more variable than from the allergen Toxicodendron. METHODS Closed patch tests with SLS or an extract o f Toxicodendron radicans (Hollister-Stier Laboratories, Spokane, WA) were applied to the forearms of volunteers after written informed consent was obtained. The population tested with SLS consisted of five male and five female subjects who had fair or average complexion and were between the ages of 18 and 34 years. T h e population tested with Toxicodendron consisted o f seven other male and three other female subjects who had fair or average complexion and were between the ages of 22 and 40 years. These latter subjects all had a history of Toxicodendron dermatitis and had previously reacted to a screening patch test with Toxicodendron antigen. Four patch tests were applied to each arm (ventrolateral surface of the mid forearm) using Al-test patches in strips occluded with Blenderm tape. The distance between test sites was 22 ram. Each patch
Volume 11 Number 3 September, 1984
Sodium lauIyl sulfate irritant patch tests. H
475
T a b l e I, Degree o f reaction at various sites at 24 hours
Subject No.
Sodium lauryl sulfate solution, 10%* 1 1 2 1 2 0 0 0 3 3 4 1 4 4 1 1 5 -+ 0 + 6 3 3 2 7 -+ + 1 8 4 3 5 9 4 3 2 10 1 1 1 Toxicodendron extract]" 1 2 2 2 2 3 3 3 3 4 4 4 4 3 3 3 5 3 2 3 6 3 3 3 7 2 2 2 8 4 4 4 9 3 3 3 10 2 2 2
Mean
S.D.
2 0 3 -+ + 3 1 3 4 1
1 0 3 1 3 1 4 4 2
2 0 4 + 1 3 1 4 4 1
1 0 4 0 1 3 ± 4 4 1
2 0 4 + 1 3 1 5 4 1
1.50 0.00 3.25 1.00 0.69 2.88 0.81 4.00 3.63 1.13
0.53 0.00 1.04 1.25 0.37 0.35 0.26 0.76 0.74 0.35
2 3 4 3 2 3 2 4 3 2
2 3 4 3 3 3 2 4 3 2
2 3 4 4 2 3 2 4 3 2
2 3 4 3 3 3 2 4 3 2
2 3 4 3 3 3 2 4 3 2
2.00 3.00 4.00 3.13 2.63 3.00 2.00 4.00 3.00 2.00
0.00 0.00 0.00 0.35 0.52 0.00 0.00 0.00 0.00 0.00
*Mean, 1.89; S.D., 1.41. tMean, 2.88; S.D., 0.75.
consisted of either 25/xl of 10% aqueous SLS or 5/M of 2% Toxicodendron oleoresin in ethyl alcohol. After 24 hours, patches were removed. The degree of inflammation was graded 5-10 minutes later and then 2, 24, and 48 hours later with an eight-point grading scale, as follows: 0 = No visible reaction __+= Barely perceptible erythema l = Mild erythema 2 = Moderate erythema 3 --= Intense erythema 4 = Intense erythema with edema 5 = Intense erythema with edema and vesiculation 6 = Intense erythema with edema and vesicular erosion RESULTS
T h e degree o f inflammation at each site is pres e n t e d in Table I. Sites 1, 3, 5, and 7 were on the right f o r e a r m , and sites 2, 4, 6, and 8 were on the left f o r e a r m . Sites 1 and 2 were nearest the elbow, and sites 7 and 8 were nearest the wrist. T h e degree o f variation among test sites was
considerably greater at sites elicited with SLS than those elicited with Toxicodendron. The total number of scores different f r o m the m e d i a n score for each subject is 27 for SLS in comparison to 4 for Toxicodendron. If the range of scores for each subject in grading point scale units is determined and summated, the total is 18 for SLS and 2 for Toxicodendron. The greater variability of scores within subjects tested with SLS, in c o m p a r i s o n to those tested with Toxieodendron, was statistically significant (Wilcoxon's r a n k - s u m test, two sided) at 24 hours (p = 0.0016). Not only was there considerable site-to-site variation in intensity of reaction f r o m SLS, but there was a considerable difference in mean reactivity among subjects in the two groups. All subjects elicited with Toxicodendron extract had mean scores between 2 and 4, whereas those elicited with SLS had mean scores ranging f r o m 0 to 4. Standard deviations for the eight tests in each subject are included in Table I, The m e a n standard
476
Journal of the American Academy of Dermatology
Dahl et al
deviation for SLS was 1.41, whereas the mean for Toxicodendron was 0.75. Corresponding sites on the left and right side scored identically 90% of the time with Toxicodendron but only 53% of the time with SLS. A similar variability was noted 2, 24, and 48 hours later. DISCUSSION The threshold of irritancy to chemicals varies considerably from subject to subject. 2,a This variation may be marked. 4''~'* Both Toxicodendron and SLS induce a wide range of reactions among subjects both in threshold and degree of reaction. In some individuals the reaction is mild, whereas in others it is severe. The variability is more marked with the irritant SLS than with the allergen Toxicodendron extract. The variation is probably relevant to clinical disease as well, since the skin of some individuals seems more susceptible to damage with irritating chemicals. The nature of protective and susceptibility factors is largely unknown, but evidence suggests that the causes of variability are multifactorial. ~ Not only did reactions to irritants differ from subject to subject, but they also differed from site to site in individual subjects. Whereas all test reactions with Toxicodendron seemed similar in a given subject, the inflammation at SLS sites varied greatly. This reaction was obvious when the arms were inspected, even at a distance. Rietschel* compared the forearm response to patch tests with aqueous solutions at 5% SLS. He also found unpredictable variability between sites, and the reasons for this variability are not apparent in his study either. According to two groups of investigators, the intensity of reaction to one irritant does not reliably predict the intensity of reaction to another. 7'~ Similarly, the intensity of reaction to SLS patch tests cannot be used as a "hyperirritability marker" for the excited skin syndrome? Since there is marked site-to-site variability in the degree of inflammation elicited by closed patch tests with SLS in a given subject, these vagaries of single test responses make comparisons between subjects or irritants un*Rietschel RL: Advances and pitfalls in in'itant and alIergic testing. J Soc Cosmetic Chem 33:309-313, 1982.
reliable. Comparative studies of irritant responses would require testing technics that minimize this variability or, alternatively, multiple tests with the same chemical to determine an average response. The wide range of reaction to irritation by SLS in a given subject at various sites underscores the apparent futility of identifying potential employees susceptible to occupational hand eczema by applying patch tests with irritants. This variability also confounds studies of therapeutic agents used to treat irritant dermatitis elicited by controlled insult. Frosch and Kligman TM have developed a chamber assay in an attempt to obtain more reproducible results. At the same time the response of a given individual's skin to the allergen in the Toxicodendron extract is relatively constant. If this is also true for other allergens, then quantitative patch test studies of allergic contact dermatitis are more likely to be valid than those of irritants. Our testing was done only at one concentration and only on the skin of the forearms. Site-to-site variations over the b o d y surface and dose response variations were not examined. The consistency of response confirms the notion that allergic contact dermatitis elicited by quantitative patch tests could serve as a model for evaluation of therapeutic agents. 4 However, often the dermatitis is so severe that inflammation is not notably suppressed, except for potent agents .4 In summary, 24-hour closed patch tests with the irritant SLS induce inflammation, but the degree of inflammation is unpredictable for site-to-site comparison in the same anatomic area (forearm). The variation is less with allergic contact dermatitis elicited by twenty-four closed patch tests with Toxicodendron extract. Although our method may be satisfactory for quantitative patch testing with strong allergens such as Toxicodendron, our study supports the observations of others that these same methods are not satisfactory for quantitative patch tests for irritants, unless the sources of variability can be identified and controlled. REFERENCES
1. MagnussenB, Hersle K: Patch test methods. II. Regional variations of patch test responses. Acta Derm Venereol (Stockh) 45:251-261, 1966. 2. Dahl MV, Trancik RJ: Sodium lauryl sulfate irritant patch tests: Degree of inflammation at various times. Contact Dermatitis 3:263-266, 1977.
Volume 11 Number 3 September, 1984
Sodium lauryl sulfate irritant patch tests. II
3. Bruynzeel DP, van Ketel WG, Scheper RJ, et al: Delayed time course of irritation by sodium lauryl sulfate: Observations on threshold reactions. Contact Dermatitis 8:236-239, 1982. 4. Kaidhey KH, Kligman AM: AssaY of topical corticosteroid. Arch Dermatol 112:808-810, 1976. 5. Skog 13, Forsbeck M: Comparison between 24-48 hour exposure time in patch testing. Contact Dermatitis 4:362-364, 1978. 6. Mathias CGT, Maibach HI: Dermatotoxicology. Monograph I. Cutaneous irritation: Factors influencing the response to irritants. Clin Toxieol 13:333-346, 1978.
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7. Czerwinska-Dihm I, Rudzki E: Skin reactions to primary irritants. Contact Dermatitis 7:315-319, 1981. 8. Bjornberg A: Skin reactions to primary irritants in patients with hand eczema. G6teberg, I968, Oscar Isacsons Trycked AB. 9. Bruynzeel DP, van Ketel WG, yon Blomberg-van der Flier M, Scheper P,J: Angry back or the excited skin syndrome: A prospective study. J AM ACADDERI~IATOL 8:392-397, 1983. 10. Frosh PJ, Kligman AM: The Duhring chamber: An improved technique for epicutaneous testing of irritant and allergic reactions. Contact Dermatitis 5:73-81, 1979.
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Sodium lauryl sulfate irritant patch tests. III. Evaporation of aqueous vehicle influences inflammatory response M a r k V. Dahl, M . D . , and Mary Jane Roering, B.S.N~
Minneapolis, MN Patch tests with aqueous solutions of the irritating detergent sodium lauryl sulfate (SLS) elicit varying degrees of inflammation from subject to subject and from site to site, For an investigation of the causes of this variability, two patch tests with 10% aqueous solutions of SLS were applied to adjacent areas o f ventral forearm skin of eighteen volunteers. In one test the water vehicle was allowed to evaporate from the patch test unit before the patches were applied. After 22 hours the patch tests were removed, and 2 hours later the degree of inflammation was graded. Less inflammation was present at the site of the dry patch test in fifteen of eighteen subjects, and the score of inflammation between each pair was significantly less at the dry patch test site (p < 0.001). These studies show that evaportion of water from aqueous solutions can influence the irritating potential of SLS on human skin. (J AM A c a o DERMATOL 11:477-479, 1984.)
A t v a r i o u s times and for various reasons, inv e s t i g a t o r s h a v e applied irritating chemicals to the s k i n o f h u m a n subjects and produced inflammat i o n . T h e d e g r e e o f inflammation elicited from
such tests is highly variable. This variability occurs not only from subject to subject but also from patch test to patch test in individual patients.1-'~'*'t S o m e causes o f this variability h a v e
From the Department of Dermatology, Universityof MinnesotaMedical School. Accepted for publication March 7, 1984. Reprint requests to: Dr. Mark V. Dahl, Box 98 Mayo, Universityof Minnesota Medical School. Minneapolis, MN 55455.
*RietschelRL: Advancesand pitfalls in irritant and allergen testing. ] Soc Cosmet Chem 33:309-313, 1982. 'l'BrownVKH: A comparisonof predictive irritation tests with suffactants on human and animal skin. J Soe Cosmet Chern 22:411-420, 1971. 477