Final Report on the Safety Assessment of Isobutylparaben and Isopropylparaben

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Abstract
Isobutylparaben and Isopropylparaben are esters with a phenol ring structure intended for use as preservatives in cosmetics. In 1993, only Isobutylparaben was reported to be in use. When administered to rabbits via a stomach tube, Isobutylparaben was metabolized primarily to p-hydroxybenzoic acid; <1% was recovered unchanged. Spleen, thymus, hepatic parenchyma, and lymph node atrophy was observed in short-term feeding studies in mice with Isobutylparaben at a concentration of 1.25%. All mice died at concentrations of 5 and 10%. Isobutylparaben at a concentration of 0.6% produced no adverse effects. Mutagenesis was not observed with either ingredient in Ames tests, but both positive and negative results were seen in chromosome abberation assays of Chinese hamster ovary cells in culture. In chronic mouse-feeding studies, 0.15, 0.3, and 0.6% Isobutylparaben caused no increase in neoplasias or decrease in time to neoplasm development. Data on Methylparaben, Ethylparaben, Propylparaben, and Butylparaben considered relevant to the assessment of Isobutylparaben and Isopropylparaben were summarized. Subchronic and chronic studies indicate that these other parabens are practically nontoxic, nonmutagenic, and noncarcinogenic. They also do not irritate or sensitize normal skin. Tests of patients with damaged skin, however, do show that a few of these individuals can be sensitized. These data support the recommendation that all six of these parabens should not be used on damaged skin. Given the absence of any adverse effects, including irritation and sensitization, in persons with normal skin, the conclusion that Methylparaben, Ethylparaben, Propylparaben, and Butylparaben are safe as cosmetic ingredients was reaffirmed. By extension, because of their similarities, the conclusion was reached that Isobutylparaben and Isopropylparaben are safe as cosmetic ingredients in the present practices of use.