Men who wear boxers during the day but go nude at night actually have 25% less DNA fragmentation in their sperm when compared to those who leave their underwear on day and night.
The study, which was carried out by the National Institute of Child Health and Human Development, Maryland, and Stanford University, followed 500 men over the course of 12 months, monitoring their underwear choices and sperm samples throughout.
The lead author of the study said "among men in the general population attempting pregnancy type of underwear worn during the day and to bed is associated with semen quality".
"Reducing exposure for bed decreases DNA fragmentation and better quality parameters are observed in men wearing boxers during the day and none in bed".
Sleeping nude not only increases fertility, it also lessens the likelihood of men developing Jock Strap Itch. But these results are nothing new according to Allan Pacey, a leading fertility expert and Professor of Andrology at the University of Sheffield.
"We have known for some time that men who increase the temperature of their testicles, either through the heat exposure at work or by wearing tight underwear, have poorer semen quality compared to men whose testicles are cooler".
"What has never adequately been shown is whether men can improve things by changing the choice of their underwear, but this study - although quite small - goes some way to suggest that is true.
"What we really need to see is whether switching to looser underwear makes their partners get pregnant more often or quicker than they would have done had the men continued to wear tight underwear".