Seminal oxidative stress (OS) is a condition where the levels of oxidants overwhelm those of the antioxidants (reductants) present in the semen [1]. The most important oxidants are reactive oxygen species (ROS), a group of oxygen-based molecules including radicals (e.g. superoxide anion – O2-.; hydroxyl radical – OH.; peroxyl radicals – ROO.; alkoxyl radicals – RO.; organic hydroperoxides – ROOH) and non-radical species (hydrogen peroxide – H2O2). Free radicals are molecules with one or more unpaired electrons in the outer orbit, which are highly reactive towards any kind of cellular components (lipids, proteins and DNA).

The investigation of the male fertility potential starts with the analysis of seminal fluid. The seminal fluid or ejaculate is composed of a heterogeneous water-based solution (seminal plasma) deriving from secretions of prostate, testes, seminal vesicles and bulbourethral glands, and cellular components that include mature spermatozoa and epithelial cells derived from the genitourinary tract as well as the generically defined “round cells” (i.e. leukocytes, Sertoli cells and germ cells) [1]. Hence, the standard semen analysis provides insight into the testicular production of spermatozoa as well as the functionality and secretory activity of the associated sex glands [2]. Moreover, it permits the identification of genetic conditions associated with male infertility, such as azoospermia or globozoospermia, and orientates the choice of treatments or the necessity for further tests and investigations. Currently, semen analysis is performed according to the most recent WHO guidelines [2], which provide instructions for the evaluation of macroscopic (liquefaction, viscosity, appearance, volume, pH) and microscopic (sperm concentration, motility, morphology, vitality, presence of round cells and agglutination zones) seminal characteristics. The lower reference value for each parameter is represented by the fifth percentile, calculated based on a selected population of 1953 recent fathers [2]. However, it should be noted that men having seminal parameters below the reference values provided can still be fertile. On the other hand, men showing seminal parameters above the lower reference values are not necessarily fertile as about 15 percent of the men are reported to be infertile despite having normal semen parameters according to World Health Organization (WHO) criteria [3].