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mythbuster graphic The style of underwear a man wears may affect his fertility, but to date, studies on the subject have not been conclusive or exhaustive. To cover all their bases, men who are trying to conceive may want to opt for loose-fitting underwear—or even none at all.

Male infertility contributes to about half of all cases when a couple can’t conceive. Most often, it is caused by a problem with the sperm itself, such as a low sperm count, poor motility (non-active or slow moving sperm), or abnormally shaped sperm.  Factors that negatively affect sperm development and motility include drug and alcohol abuse , diabetes , and bacterial infections. Environmental factors include toxic exposure to chemicals or radiation and overheated testicles. The reasons for many cases of low sperm quality go unresolved.

As a matter of routine, many fertility clinics suggest that men trying to conceive should wear boxer shorts instead of briefs or tight-fitting underwear. Why? Briefs position the scrotum closer to the abdominal cavity, which may slightly raise its temperature. Increased scrotal temperature can reduce sperm production and motility. But the evidence supporting the boxers-over-briefs advice is pretty weak.

Evidence for the Health Claim

A few studies have shown a decrease in sperm concentration and motility when subjects wore tight-fitting underwear compared to loose-fitting underwear (such as boxer shorts). It is worth noting that most of these studies were conducted on very small numbers of subjects. One study published in the Lancet included nine subjects; another published in Reproductive Toxicology studied only two subjects.

However small, both of those studies concluded that wearing tight-fitting underwear does increase scrotal temperature enough to significantly reduce sperm count and motility. Neither of these studies, though, suggested that the deleterious effect on sperm was long-lasting.

One of the largest studies supporting the claim was conducted on 50 men at Leibig University in Germany. Its results indicated that high scrotal temperatures (defined as near body core temperature) negatively affected spermatogenesis (the development of mature sperm cells). The German study, published in Human Reproduction , measured scrotal temperatures on men wearing cotton jockey briefs, cotton boxer shorts, or no underwear, and compared the temperatures after the men completed physical activity (walking for 45 minutes on a treadmill), and after they sat in a fixed position for 45 minutes. The study found significantly higher scrotal temperatures while the subjects wore jockey briefs versus boxers, regardless of activity level, and the lowest scrotal temperatures when the subjects wore no undergarments.

Evidence Against the Claim

A study published in the Journal of Urology measured scrotal, core, and skin temperatures in 97 men, and semen samples were compared. Additionally, a crossover group of 14 men alternated underwear type and then had temperature readings repeated for comparison. The results found no statistically significant differences in scrotal temperature or semen quality between the groups, and the study’s authors concluded that “it is unlikely that underwear type has a significant effect on male fertility.”

A Norwegian study conducted on 252 men measured sperm quality, motility, volume, and other factors, and correlated those factors with exposure to heat (including sauna and hot tub exposure and type of underwear worn) as reported by the subjects. Results indicated that the lifestyle of the male subject had little, if any, impact on semen quality.

Conclusion

It’s a fact that overheating the testicles can result in impaired sperm production, and it is also true that the ideal temperature for sperm production is slightly lower than core body temperature.

A few studies on a limited number of subjects support the belief that tight-fitting underwear can cause enough of a temperature increase to impair sperm development and production. However, some larger studies did not find that temperature differences caused by underwear styles are great enough to be of any clinical significance.

The bottom line? There is no reason for would-be fathers to give up their briefs. However, if a couple is having trouble conceiving, it certainly couldn’t hurt to add room down there.

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