Toxicodendron antigen patch test. Degrees of inflammation observed after various time intervals

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.