Mercury is one of the widespread toxic metal detrimental effects on human health. Humans can be exposed to mercury in the workplace, consume large amounts of aquatic product, products containing mercury such as traditional remedies, cosmetics, including skin lightening creams. The aim of this review is to explore the natures and type of mercury, routes of exposure and sources of mercury, toxicity mechanisms of mercury exposure, and the clinical signs of acute and chronic exposure of mercury. The writing methodology used is a literature review. The literature source consists of relevant journals and books from the search engines PubMed and Google Scholar. The major sources of mercury in the environment are divided into two types; natural and anthropogenic sources. Mercury typically exists in in three forms, including elemental mercury, inorganic mercury and organic mercury. Toxic effect of the mercury was documented in several historical accidents that revealed by neurological symptoms, the cardio metabolic syndrome, liver and renal diseases via the oxidative stress mechanisms, due to the strong ability of the mercuric compounds to bind to the sulfhydryl terminal of vital proteins and enzymes.