Peroxynitrous acids, also known as peroxynitric acids, are a group of highly reactive chemical substances. They are formed by the reaction of nitric oxide (NO) with superoxide (O2-) radicals. These acids play a crucial role in various biological processes and have been linked to numerous health conditions. Synonyms for peroxynitrous acids include peroxynitric acid, nitroperoxide, PN(O)OH, and nitroso-peroxy compounds. These terms are often used interchangeably to refer to the same chemical entity with slight variations in molecular structure. Despite different names, they all describe the same highly reactive, potentially harmful compounds produced in the body. Understanding and studying the effects of peroxynitrous acids is essential in advancing knowledge about their involvement in oxidative stress and their potential implications in disease development and progression.