Psychological stress is harmful to sperm and semen quality, affecting its concentration, appearance, and ability to fertilize an egg, according to a study. 

Possible explanation could be that it may trigger the release of steroid hormones called glucocorticoids, which in turn could blunt levels of testosterone and sperm production. Another possibility is oxidative stress, which has been shown to affect semen quality and fertility. 

"Men who feel stressed are more likely to have lower concentrations of sperm in their ejaculate, and the sperm they have are more likely to be misshapen or have impaired motility," says senior author Pam Factor-Litvak, PhD, associate professor of Epidemiology at the Mailman School of Public Health. "These deficits could be associated with fertility problems."