Induction of antigen specific hyposensitization to poison oak in sensitized adults.

Twenty-one adults, highly sensitive to urushiol, the allergen in poison oak/ivy, ingested up to 300 mg of urushiol over three to six months. A control group received placebo capsules. The study was done double blind to evaluate changes in patch test reactivity to urushiol, altered reactivity to an unrelated contract sensitizer, side effects, and duration of hyposensitization. A significant number of subjects in the experimental group (15/21) became hyposensitized. Such hyposensitization was not seen in the control group (2/12), and the difference between groups was significant. No change in reactivity to an unrelated contact sensitizer occurred in subjects hyposensitized to urushiol, suggesting antigen specificity. Retesting up to three months after completion of the protocol indicated that subjects remained hyposensitized without a "rebound" effect during the time. Side effects, detected by questionnaire, were limited to vesicular and urticarial rashes and pruritus ani in 18 of 21 test subjects.