Because of their highly reactive nature and potentially toxic characteristic, reactive oxygen species (ROS) have had a bad reputation for years. However, under certain conditions, ROS generation has shown positive outcomes. It is ROS imbalance that causes toxic effects. ROS play an important role in physiological processes such as cell signaling, senescence, inflammation, and the immune response to infection. An increasing number of studies highlight the importance of ROS for the inflammatory response, whether sterile or due to infection or cancer. The purpose of this paper is to present evidence of the essential role of ROS in the inflammatory response.