Free radicals and other reactive oxygen species (ROS) are manly formed endogenously during oxidative phosphorylation inside our cells. During this process, energy in the form of ATP is obtained from ingested food. Compounds from the food react with oxygen and carbon dioxide, water and energy are released. More precisely, each molecule of oxygen is reduced in 4 step reaction into water. However, the mentioned reaction is not 100 % efficient due partial reduction of oxygen which leads into formation ROS. Due to their reactivity ROS molecules cause damage to the cell macromolecules. Unfortunately, there is little we can do regarding the formation of ROS from the endogenous source. The second source of ROS-causing damage to human cells originates from the environment we are living. We are constantly exposed to diverse oxidizing products like: ozone, nitrogen oxides, ionizing and non-ionizing radiation (e.g., UVradiation), various pesticides, alcohol, disinfection by-products, cigarette smoke, etc. In the case of exogenous ROS exposure we have partial influence: we can either move to the environment with less ROS-sources or we can protect ourselves with ingestion of antioxidants. In the article, data will be discussed, whether it is reasonable to increase our defense against environmentaly-induced oxidative stress with antioxidants or not.