Oxidative stress occurs when the generation of reactive oxygen species (ROS) and other radical species exceeds the scavenging capacity by antioxidants due to excessive production of ROS and/or inadequate intake or increased utilization of antioxidants. Most ROS are formed as a consequence of the mitochondrial respiratory chain, but can also be formed by exogenous exposures such as alcohol, tobacco smoke, and environmental pollutants. Antioxidants (including vitamins C and E) and antioxidant cofactors (such as selenium, zinc, and copper) are capable of disposing, scavenging, or suppressing the formation of ROS. Evidence exists supporting the role of oxidative stress in male subfertility, including decreased sperm motility, sperm number, and sperm–oocyte fusion . In women, several animal and in-vitro studies suggest that oxidative stress may affect female fertility .