The European Society of Human Reproduction and Embryology found that men who wear boxer shorts have higher sperm counts than men who wear tight-fitting underwear. This study, published in the journal Human Reproduction, is the largest ever on this subject and the first to go beyond simply counting sperm into the biological function of how a man makes the best sperm.
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Researchers found that boxers stimulated lower levels of the hormone needed for sperm production. This doesn't sound positive on the surface until we understand that the higher hormone levels for briefs-wearers is to compensate for the testicular damage caused by the heat of wearing tight-fitting underwear. When the scrotum gets too hot, sperm counts go down. So those who wear briefs end up making much more of this sperm-making hormone as an attempt at damage control.
Men who wear boxers have 33 percent more sperm in a single ejaculation, a 25 percent higher sperm concentration, a 17 percent higher sperm count, more high-quality sperm, and yet 14 percent lower sperm-making hormones.
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"Since men can modify the type of underwear they choose to wear, these results may be useful to improve men's testicular function," said lead study author Lidia Mínguez-Alarcón.
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