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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 less than 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.

Allergic contact dermatitis was elicited with Toxicodendron antigen and the patch test site examined at various time intervals up to one week. The degree of inflammation was rather constant during the observation period. The mean erythema score at 168 hours was not significantly different from the score at 24 hours. These data support the use of a delayed (96-hour) patch test reading as a guide to discriminating between allergic and irritant patch test reactions.