Abstract

are the most common preservatives in skin care products. Alone or in combination with other compounds they are used as a preservative to protect microbial growth in skin care products. Parabens have been successfully used by the cosmetics and pharmaceutical industries for more than 60 years. Parabens are alkyl esters of p-hydroxybenzoic acid. There are seven types of parabens available in the market. However, mostly four types of parabens are commonly used in cosmetics products; these are methyl paraben (MP), ethyl paraben (EP), propyl paraben (PP), and butyl paraben (BP). Those are esterified with an alkyl chain which is structurally reliable for anti-microbial activities. Paraben safety studies proved that parabens are safe for the human body. Therefore, The United States Food and Drug Administration approved parabens as preservatives in skin care products and they set a concentration of 0.4% w/w in a single paraben and 0.8% w/w in a combination of parabens. However, recent studies on the effects of parabens reported that they exhibit estrogenic activity on human skin. Thus, The Danish government banned all paraben use in cosmetics. Although, European Union (EU) government regulatory boards claim that current concentrations of parabens in skin products are safe for cosmetic products. Consequently, there is conflicting evidence over the safety of parabens used as preservatives in skin care products.
This research is presented in three chapters. The first chapter explains the feasibility of addressing the safety of parabens through cytotoxicity assay and establishes a ranking order of paraben safety according to their toxicity. This study was conducted with an SRB assay. In the second chapter, the % metabolism of parabens through pig skin has been studied. Pig skin was chosen because it has similar histological and physiological properties to human skin. The permeation of parabens through Franz diffusion cells was determined over 24 hours using HPLC analysis for the quantification of parabens and their metabolite. This permeability study described a comparative analysis of parabens metabolized through pig skin and established a ranking order of paraben permeation according to their rate of metabolism. In the third chapter, we investigated the metabolism of parabens in human keratinocyte cells. The recommended concentration of each paraben was incubated with human keratinocyte cells at three different times of incubation. After incubation, parabens and their metabolite were extracted by lysis buffer and quantified using HPLC analysis. During this study, the % metabolism ranking order of these parabens in human keratinocytes was also determined.