Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous pollutants released from the incomplete combustion of fossil fuels and are always found as a mixture of individual compounds. Due to economic growth and a sharp increase in energy consumption in recent years, large quantities of PAHs have been released into the environment worldwide. Because many PAHs and their derivatives are strongly potent carcinogens, or mutagens, PAHs have been extensively studied recently. The authors reviewed the origin and distribution of PAHs in atmosphere, soil, and sediment in natural environments. PAHs represent a class of toxicological compounds that can create a variety of hazardous effects in vivo/in vitro, including genotoxicity, immunotoxicity, developmental toxicity, and carcinogenesis, which the authors also describe.