Assessment of the elicitation response in subjects weakly sensitized to p-phenylenediamine

BackgroundA 30-min application of a hair dye product containing 2% p-phenylenediamine (PPD) to subjects diagnostically graded +, showed that 12 of 18 reacted; eight of 18 with a true + and four of 18 with a doubtful (?+) response, whereas six of 18 did not react at all. In vitro skin-binding experiments showed that for diagnostic patch test conditions the measured exposure level (MEL) is more than 10-fold higher than the MEL for hair dyeing conditions.

ObjectiveTo further analyse the limited elicitation response of the diagnostically + graded subjects to a PPD hair dye product, under standardized test conditions mimicking product usage, by varying exposure time and dose.

MethodsA hair dye model formulation containing 2% PPD, applied for 30, 45 and 60min and a diagnostic PPD TRUE test((R)) were applied to assess elicitation responses to increasing PPD exposure levels. Grading was performed according to International Contact Dermatitis Research Group guidelines.

ResultsSix subjects were available for this follow-up study. One of six subjects responded with a + elicitation response to the hair dye model applied for 60min. Four of the five remaining subjects elicited a+response to the PPD TRUE test((R)) applied subsequently, while one of five responded doubtfully.

ConclusionsIncreasing the PPD exposure time twofold - resulting in a 5-6% increase of sensitivity of this hair dye model test - or further extending the exposure time 48-fold, was found sufficient to increase the MEL above the thresholds needed to elicit individuals with a+diagnostic PPD patch test who did not react to typical hair dye use conditions with a MEL of about 68gcm(-2). This analysis confirms that consideration of the MEL is a useful tool to better characterize thresholds of elicitation than consideration of the applied dose alone.