Even free radicals should follow some rules: A Guide to free radical research terminology and methodology

Free radicals and oxidants are now implicated in physiological responses and in several diseases. Given the wide range of expertise of free radical researchers, application of the greater understanding of chemistry has not been uniformly applied to biological studies. We suggest that some widely used methodologies and terminologies hamper progress and need to be addressed. We make the case for abandonment and judicious use of several methods and terms and suggest practical and viable alternatives. These changes are suggested in four areas: use of fluorescent dyes to identify and quantify reactive species, methods for measurement of lipid peroxidation in complex biological systems, claims of antioxidants as radical scavengers, and use of the terms for reactive species. [Display omitted] •Dye oxidation alone is insufficient evidence for detection of reactive species in biology.•Nonenzymatic lipid peroxidation assessment requires product analysis by mass spectroscopy.•Antioxidant claims require quantitative dose–response lowering of oxidative stress.•“ROS” and “RNS” should be used only when defined and the actual species are unknown.