Abstract: Hormesis is a phenomenon characterized by a stimulation to the host triggered by a low dose of external stressors and an inhibition by a high dose, which is different from the classic concept of traditional dose-response relationship in toxicology. Studies suggest hormetic effect occurs in a variety of pollutants at low dosage. Thus, the findings of high-dose exposures inform previous eco-toxicity studies could not apply to the risk assessment of low-dose pollutants. This paper reviewed the advances in hormesis studies, with the focus on its historical foundation, generalization and possible mechanisms. Comments were provided on implications of hormesis in risk assessment. Key orientations of future research were also proposed.