Parabens (p-hydroxybenzoic acid esters) which have been widely applied in the processing of foods, pharmaceuticals and cosmetics for more than 50 years, include methyl-paraben, ethyl-paraben, propyl-paraben, butyl-paraben, heptyl-paraben and benzyl-paraben. The major metabolite of parabens in human body is p-hydroxybenzoic acid. Nowadays, these chemicals are commonly detected in blood and urine samples. Recent studies show that the happening of breast cancer is likely related to parabens. Animal experiments indicated that parabens maybe have estrogen activities. Therefore the occurrence, pollution, and toxicity of parabens in environment and human tissue attracted much more attention recently. Publications on parabens in environment matrix (external exposure routes) and human tissues (internal exposure) are comprehensively reviewed in this review. Firstly, the concentrations of parabens in food, pharmaceuticals, cosmetics, air, dust, water and soil are summarized, and the dose of external exposure is estimated accordingly. Then, the published concentrations of parabens in human blood, urine and adipose tissue are applied for the estimation of internal exposure. The external exposure dose and the internal exposure dose are compared and discussed, which provide the new insight into the main exposure route of parabens for general population. Finally, the critical areas of research on parabens that warrant further attention are discussed.

Contents
1 Introduction
2 Exposure pathways and metabolic process
3 External exposure routes
3.1 Food
3.2 Personal care products
3.3 Medicine
3.4 Other environmental sources
4 Internal exposure routes
4.1 Urine
4.2 Blood
4.3 Adipose tissue
5 Comparison of internal and external exposure
6 The deficiencies of recent studies
7 Outlook