Characteristics of patch test reactions to common preservatives incorporated in petrolatum and water, respectively

The irritant properties of some preservatives and the use of water as the patch test vehicle for some of them call for a critical evaluation of patch test reactions to preservatives.

To examine the association between test vehicle (petrolatum versus water) or the patients' age and history of atopic dermatitis, respectively, and certain patterns of reaction to preservatives.

Data of 34,631 patients tested in 34 centres with 11 common preservatives were retrospectively analysed. The dynamic reaction patterns, reaction indices (RIs) and positivity ratios (PRs) were statistically evaluated.

All preservatives yielded more crescendo reactions in older than in younger patients. For 10 of 11 preservatives, the percentage of crescendo reactions was slightly higher in patients without a history of atopic dermatitis, and for 10 of 11 agents the RI was higher in patients with a positive history of atopic dermatitis. No consistent vehicle-related effects on reaction characteristics were found. Chlorhexidine digluconate 0.5% in water and sodium benzoate 5% in petrolatum had the lowest RIs, highest PRs, and lowest proportions of crescendo reactions.

Water as a vehicle is unlikely to affect the reaction patterns of preservatives. The generally used patch test preparations of chlorhexidine digluconate and sodium benzoate need improvement.