Does Wearing Loose Boxers Lower FSH?
No, wearing loose boxers does not lower FSH levels in men. The evidence shows that while underwear type may have minimal effects on sperm parameters, there is no demonstrated impact on FSH levels, with the exception of one study showing the opposite relationship.
Evidence on Underwear Type and FSH
The single highest-quality study directly addressing this question found that men who primarily wore boxers had 14% lower serum FSH levels compared to men who wore tighter underwear 1. However, this finding suggests that loose underwear is associated with already lower FSH rather than causing FSH to decrease—the cross-sectional design cannot establish causation 1.
The proposed mechanism is that tight underwear may impair spermatogenesis through increased scrotal temperature, triggering a compensatory increase in FSH secretion by the pituitary 1. This means elevated FSH in tight-underwear wearers reflects testicular dysfunction, not that switching to boxers actively lowers FSH 1.
Evidence on Underwear Type and Sperm Parameters
Studies Showing Minimal or No Effect
A critical analysis of 97 consecutive subfertile men found no significant difference in scrotal temperature between boxer and brief wearers (33.8°C vs 33.6°C), and no differences in semen parameters 2.
A preconception cohort study of 491 men found that underwear choice was associated with few differences in semen parameters, and after controlling for multiple comparisons, no differences remained significant 3. Importantly, no association with time-to-pregnancy was observed 3.
Studies Showing Possible Benefits
Men who primarily wore boxers had 25% higher sperm concentration and 17% higher total sperm count compared to non-boxer wearers 1. However, these differences were attenuated after adjusting for FSH levels, suggesting FSH mediates the relationship 1.
A small pilot study of two men showed semen parameters gradually decreased in tight conditions and increased in loose conditions over alternating 3-month periods 4. This study is severely limited by sample size and lacks statistical power 4.
Guideline Perspective on Heat Exposure
Current guidelines conclude there is insufficient evidence that clothing type affects male fertility. The WHO guidance analysis states: "We strongly recommend, based on a very low quality of evidence, that there is insufficient evidence to conclude that exposure to heat, be it occupational or as a result of clothing or body position, affect semen quality and/or male fertility" 5.
Key Limitations in the Evidence
Most studies linking activities to increased scrotal temperature do not follow up with fertility outcomes like live birth rate or time-to-pregnancy 5.
Studies suffer from small sample sizes, lack of control groups, retrospective data collection, and confounding lifestyle factors 5.
No randomized controlled trials exist, and no systematic reviews or meta-analyses have been performed due to significant variation in study design 5.
Some studies attribute differences in semen parameters to activities without actually measuring scrotal temperature 5.
Clinical Bottom Line
Switching to loose boxers will not lower FSH in men with elevated FSH. Elevated FSH reflects underlying testicular dysfunction—whether from genetic causes, prior exposures, or primary testicular failure 6. The testicular damage has already occurred, and changing underwear cannot reverse it.
What Actually Matters for Elevated FSH
FSH >7.6 IU/L indicates some degree of testicular dysfunction and warrants semen analysis 6.
Evaluate for reversible causes: thyroid dysfunction, obesity, metabolic syndrome, medications, and environmental exposures 5, 6.
Genetic testing (karyotype and Y-chromosome microdeletions) is essential for FSH elevation with oligospermia or azoospermia 6.
Even with elevated FSH, up to 50% of men with non-obstructive azoospermia have retrievable sperm with microsurgical testicular sperm extraction 6.
Practical Advice
While the evidence does not support recommending underwear changes as a fertility treatment 5, 2, 3, wearing looser underwear is unlikely to cause harm and may provide marginal benefit in the context of other lifestyle optimizations 1. However, this should never be presented as a primary intervention for elevated FSH or infertility 5.