Some Alkyl Hydroxy Benzoate Preservatives (Parabens) Are Estrogenic

Abstract

The inadvertent estrogenicity of certain synthetic chemicals, and their subsequent effects on the endocrine system of humans and wildlife, is of concern. In this paper we report findings fromin vitroandin vivo(uterotrophic) studies which confirm that a range of alkyl hydroxy benzoate preservatives (parabens) are weakly estrogenic. In a receptor-binding assay, butylparaben was able to compete with3H-estradiol for binding to the rat estrogen receptor with an affinity approximately 5 orders of magnitude lower than that of diethylstilboestrol, and between 1 and 2 orders of magnitude less than nonylphenol. In anin vitroyeast-based estrogen assay, the four most widely used parabens (namely methyl-, ethyl-, propyl-, and butylparaben) were all found to be weakly estrogenic with the most potent (butylparaben) being 10,000-fold less potent than 17β-estradiol. The estrogenic activity of parabens was inhibited by 4-hydroxy tamoxifenin vitro,illustrating the requirement of these chemicals to interact with the estrogen receptor in order to activate the yeast. When administered orally to immature rats, the parabens were inactive. However, subcutaneous administration of butylparaben produced a positive uterotrophic responsein vivo,although it was approximately 100,000 times less potent than 17β-estradiol. Given their use in a wide range of commercially available topical preparations, it is suggested that the safety in use of these chemicals should be reassessed, with particular attention being paid to estimation of the actual levels of systemic exposure of humans exposed to these chemicals. The acquisition of such data is a prerequisite to the derivation of reliable estimates of the possible human risk of exposure to parabens.