Comparison of open and closed patch tests with oleoresins was done on a group of patients with active dermatitis venenata. Equalization of positive reactions from open and closed patch tests occurred during the interval between the initial reading and subsequent observation. If epidermal sensitivity was slight, only a positive closed patch test occurred. This accounted for the difference (13%) between the open and closed patchtest results reported in this study.
SPENCER MC. Open Versus Closed Patch Testing With Oleoresins. Arch Dermatol. 1966;93(1):47–48. doi:10.1001/archderm.1966.01600190053009