Boxers vs. Briefs: What Research Shows

Alright, so heat is the enemy of sperm. But where do underwear choices come in? The logic is straightforward: tight-fitting underwear (like briefs or snug boxer-briefs) hold the testes closer to the body, potentially raising their temperature, whereas loose boxers let things hang a bit freer and cooler. For decades, this was common advice from fertility doctors – “switch to boxers if you’re trying for a baby” – even before solid data was available [2]. Now, science has started to catch up to this age-old question.

Different styles of men’s underwear offer varying degrees of snugness and breathability, which can influence scrotal temperature.

A large 2018 study from Harvard finally put some numbers to the boxers vs. briefs debate, and the results were eye-opening. Researchers looked at 656 men attending a fertility clinic and asked them about their preferred underwear style, then measured their sperm quality [1]. Men who mainly wore loose-fitting boxer shorts had 25% higher sperm concentration and 17% higher total sperm count compared to men who typically wore tight underwear (like briefs or jockeys) [1]. The boxer-wearers also had a higher percentage of motile sperm (the ones that swim well) on average [1]. These are not minor differences – they suggest a meaningful boost in sperm health associated with looser undies. Notably, the biggest gaps in sperm counts were seen between the extremes (boxers vs. the tightest styles) [1].

What could explain this? The same study checked the men’s reproductive hormones and found an interesting clue: the tight-underwear group had significantly higher follicle-stimulating hormone (FSH) levels in their blood [1]. FSH is a hormone that the brain sends to the testes to crank up sperm production. Higher FSH in the men wearing briefs suggests their bodies were compensating for chronically warmer testicles and somewhat lower sperm output [1]. In other words, tight underwear might have been impairing sperm production just enough that the brain responded by boosting FSH to try to help the testes along [1]. This hormonal evidence reinforces the idea that underwear choice was affecting testicular function.

It’s important to note that this kind of study shows association – men in boxers tended to have better sperm counts – but it wasn’t a controlled trial where guys were forced to change underwear styles. So, cautious scientists will point out that there could be other factors at play (for instance, maybe men who choose boxers also tend to do other healthy things). However, the researchers did adjust for things like body weight, and the link persisted. Moreover, these findings aren’t completely new – they basically confirmed earlier, smaller studies and what many fertility specialists long suspected [2]. A 2012 UK study of over 2,000 men similarly found that those favoring boxer shorts were less likely to have low motile sperm counts [2]. Taken together, a body of evidence now supports the notion that tighter underwear can mildly but significantly impair sperm production [2]. As one reproductive health professor put it, this is a “reasonable low-cost, low-risk lifestyle change” for men with suboptimal sperm, even if we can’t ethically blind-test it like a drug trial [2].

That said, let’s keep the findings in perspective. The differences in sperm count between boxers and briefs, while significant on average, did not typically spell disaster for the tight-underwear guys. In the Harvard study and others, even men in briefs generally still had sperm counts in the normal range – they were just on the lower side of normal, on average [2]. No one is saying that wearing briefs will make you infertile by itself. In fact, a 2016 prospective study went a step further and looked at actual fertility outcomes (like how long it took couples to conceive) and found no statistically significant difference whether men wore boxers or briefs [8]. In that study of 500 couples trying to have a baby, underwear choice showed only minor differences in semen parameters and did not affect time-to-pregnancy or pregnancy rates [8]. This is reassuring: it suggests that for most men, underwear alone isn’t a make-or-break factor for having children. Fertility is multifaceted, and sperm count fluctuates due to many influences.

So where do we land on boxers vs. briefs? The consensus among experts is something like: “The jury is still out, but it certainly can’t hurt to wear looser underwear when you’re trying to conceive” [2]. We know elevated scrotal temperature is bad for sperm [7]. We know tight clothing raises scrotal temperature a bit (typically by about 0.5–1°C in studies) [3]. Whether that small bump causes meaningful fertility issues is hard to prove conclusively [3]. But since switching from briefs to boxers is an easy, side-effect-free change, many doctors advise it as a precautionary measure [2]. It’s a bit of common sense paired with some supportive evidence. As one researcher quipped, maintaining a cool scrotum is “one easy change that can only be beneficial” for men’s reproductive health [2].