Chapter 37: Preservatives

INTRODUCTION

Preservatives are integral ingredients in various food, pharmaceutical, cosmetic, and skin care formulations. As water is included in the majority of such products, preservatives are added to prevent the growth of microorganisms and the resultant rapid deterioration or decomposition of the product. Indeed, without preservatives, which are biocidal chemicals, these items important to daily life would exhibit little to no shelf life and become quickly invaded and permeated by numerous bacteria, fungi, and molds. As such, preservatives are intended to maintain the integrity of the product and protect the user from infection.¹ While antimicrobial preservatives are essential components in the majority of cosmetics and skin care products, these ingredients have been cited frequently as causes of allergic contact dermatitis.^1–3 Such occurrences are most often associated with topical application on damaged or broken skin. Of greater concern in recent years has been the reports linking the use of some skin care products with cancer incidence. This chapter will focus on the most frequently used class of preservatives, recent data regarding the estrogenic potential of these compounds, and the controversy regarding possible associations between the chronic use of chemical preservatives that make contact with the skin and cancer.

PARABENS

Parabens, alkyl esters of p-hydroxybenzoic acid (PHBA), which are found naturally in some fruits, are common ingredients in food, pharmaceuticals, as well as numerous skin, hair, and body care products, and can sometimes produce allergic reactions.⁴ Nevertheless, parabens are the most widely used preservatives in cosmetics,⁵ and are used in the vast majority of skin care formulations.⁶ In fact, about 25 years ago, it was estimated that at least 90% of personal care products, including deodorants, toothpaste, shampoo, body cream, shower gels, moisturizers, etc., contained one or more parabens as a preservative,⁷ because of the strong record of efficacy, safety, and stability exhibited by this group of compounds. The frequency of inclusion of these ingredients has not markedly changed during the last quarter of a century despite the introduction or synthesis of new substances. The use of parabens in pharamaceutical products as preservatives actually dates back to the 1920s.⁸ These chemicals have been generally regarded as safe because they are quickly absorbed and hydrolyzed into the less toxic PHBA.³ It is also worth noting that the metabolism of parabens is influenced by the inclusion in cosmetic preparations of penetration enhancers, which facilitate the rapid absorption of parabens through intact skin.^9,10 There have been several reports of contact sensitivity associated with cutaneous exposure to parabens, but while this mechanism has not yet been fully elucidated, such occurrences, as stated above, are linked to contact with damaged or broken skin.

The family of parabens include methyl paraben (MP), ethyl paraben, butyl paraben, isobutyl paraben, propyl paraben, isopropyl paraben, and benzyl paraben.¹¹ Methyl, ethyl, propyl, and butyl paraben are the most frequently used parabens in cosmetic ...