Allergic contact dermatitis from propyl gallate: dose response comparison using various application methods

The antioxidant propyl gallate, in a deodorant product, caused an allergic contact dermatitis in 1 subject during developmental controlled use testing. Subsequent dose response elicitation studies with this subject revealed a differing threshold of sensitivity to propyl gallate dependent upon application method. Increasing the level of occlusion increased the elicitation response. Responsiveness from greatest to least was: occluded patch on the upper arm greater than semi-occluded axilla greater than open application on the antecubital fossa. The thresholds determined for propyl gallate (w/v in 25:75 ethanol:water) were: (a) 0.0025% for the upper arm occluded patch; (b) 0.0035% for the underarm without shaving; (c) 0.005% for the underarm with shaving; (d) 0.015% for the antecubital fossa. Occluded patch responsiveness to propyl gallate was monitored and remained unchanged throughout a 2-year period. These data are useful in understanding the relationship between occlusive allergic contact dermatitis patch testing and clinical contact dermatitis.