What an andrologist/urologist should know about free radicals and why.

f t f ree radicals are a group of highly reactive chemical molecules that have one or more unaired electrons and can oxidatively modify bimolecules that they encounter.1 Reactive oxygen pecies (ROS) are free radicals that are derived rom the metabolism of oxygen. They are present n all aerobic organisms. ROS play an important ole in many physiologic functions such as phagoytosis, which is mediated by neutrophils and macophages. They also act as a cell messenger, taking art in many signaling processes, mainly by oxidaively modifying the compounds.2 However, ROS re highly reactive, and when their levels are high, hey can react with any nearby molecules and cause efects in the functioning of these molecules. Oxdative stress is a condition that occurs as a result of xcessive generation of ROS and diminished capacty of free radical scavenging by antioxidants.3 Many iseases, including cancer, are thought to be the onsequence of reactions between free radicals and NA, resulting in germ line mutations that are ransmitted to offspring.4 Some pathologic proesses such as aging, ischemic heart disease, sickle ell anemia, and rheumatoid arthritis are also atributed to free radical-induced oxidation of varius biologic components.5 ROS include the various radicals such as superxide, hydroxyl, peroxyl, and hydrogen peroxide. n addition, another class of free radicals that are itrogen derived is called reactive nitrogen species. hey are considered a subclass of ROS.6 Nitrous xide, peroxynitrite, nitroxyl anion, and peroxynirous acid are some of the most common reactive itrogen species.