Macro- and microscopic alterations in 2 rabbit skin regions following topically repeated applications of benzoic acid n-alkyl esters.

This paper explores the irritancy potential of n-alkyl benzoate preservatives (methyl benzoate, MB; ethyl benzoate, EB; n-propyl benzoate, n-PB; n-butyl benzoate, n-BB), allowable in cosmetic formulations. Comparative experiments were carried out involving repeated daily application for all compounds (up to maximum of 6 days) on clipped rabbit skin in 2 distinct regions: the dorsum (0.5 ml per treatment) and the external surface of the outer ear (0.2 ml per treatment). According to the different anatomo-physiological features, benzoates elicited dissimilar reactions in the dorsum and the external ear. In the first mentioned area, there were widespread inflammatory reactions accompanied, in some cases, by necrotic changes and slight epidermal hyperplasia; on the other hand, hyperplasia was the most prominent and earliest alteration in the ear. The irritancy potential was closely related to the duration of treatment as well to the increase in the molecular weight of benzoates.