Comparison of colophony patch test preparations

The patch test reactivity to different petrolatum preparations and concentrations of colophony (gum rosin) was compared. A serial dilution test with gum rosin 20%-0.001% gave a clear dose-response relationship with a maximum response to 10% and 20%. Patch testing with 60% in the routine test did not reveal any further cases compared to simultaneous testing with 20%. Irritancy to the 60% concentration was seen in some cases. A good correlation in reactivity was found between commercially-supplied test preparations for routine testing and homogeneous preparations made up in our laboratory. Our results imply that a concentration of 10% is well worth considering for routine testing.