FACT CHECK: Does polyester underwear drop sperm count to zero?

CLAIM:

The post claims that wearing 100% polyester underwear can cause sperm counts to drop to zero over time by trapping heat around the testes. It further suggests that the effect is reversible and that switching to breathable cotton underwear can restore sperm production.

FACT:

False. Current evidence does not support the claim that ordinary polyester underwear causes sperm counts to drop to zero in most men. While a few older, small-scale studies reported reversible reductions in sperm production under specific experimental conditions, larger and more recent studies have not found a consistent link between polyester underwear and azoospermia. Experts say that factors such as heat exposure, tight-fitting clothing, overall health, lifestyle habits, and underlying medical conditions are far more important determinants of sperm quality and fertility than the fabric used in underwear.

Ever wondered whether the clothes you wear could affect more than just your comfort? From debates over tight jeans and synthetic fabrics to claims about fertility and reproductive health, what we wear has long been a topic of discussion. Among the many questions that surface online, one recurring claim is whether certain types of underwear can actually affect sperm production. 

A recent Instagram post by 'Viralsarcasm', a page with over 2.1 million followers, has brought this claim back into the spotlight. The post mentions that, "Men in polyester underwear saw sperm counts drop to zero according to studies." 

The caption further suggests that synthetic fabrics may have a significant impact on male reproductive health. According to the post, "Studies show that wearing 100% polyester underwear traps heat and can plummet sperm counts to zero over time." It also claims that the effect is "totally reversible just by switching back to breathable cotton." 

Describing polyester underwear as a hidden health risk, the post encourages viewers to "check your tags today" and asks, "What is your go-to fabric for the gym?" The claim has since attracted attention online, raising questions about whether the type of fabric used in underwear can truly reduce sperm counts to zero. 

Does polyester underwear drop sperm count to zero? 

While some older studies suggested that prolonged use of specially designed polyester garments could suppress sperm production under experimental conditions, the broader body of evidence does not support the claim that ordinary polyester underwear causes sperm counts to drop to zero in most men. Current research suggests that factors such as heat exposure and underwear tightness may have modest effects on some sperm parameters, but there is insufficient evidence to conclude that polyester fabric alone causes severe or permanent infertility. 

One of the most frequently cited studies, published in 1992, followed 14 healthy men who wore a specially designed polyester scrotal sling continuously for 12 months. According to the researchers, "all men became azoospermic after a mean of 139.6 ± 20.8 days," meaning that no sperm were detectable in their semen during the study period. The researchers also observed reductions in testicular volume and changes in testicular temperature regulation. Importantly, sperm counts returned to pre-study levels after the polyester sling was discontinued, and all five couples who wished to conceive after the study were able to achieve pregnancy. 

The authors concluded that "fertile men can be rendered azoospermic by wearing the polyester sling" and suggested that the effect was caused by a combination of altered thermoregulation and electrostatic charges generated by friction between the polyester fabric and the scrotal skin. 

To further investigate this proposed mechanism, the same researchers published another study in 1992 examining electrostatic charges generated by different fabrics. The study involved 21 healthy volunteers wearing underwear made from 100% polyester, 100% cotton, or a polyester-cotton blend. The researchers found that polyester fabrics generated the highest electrostatic potentials, while cotton generated none. According to the authors, these electrostatic fields "may disturb the testicles and/or epididymis leading to disordered spermatogenesis." 

However, these early findings should be interpreted with caution. The studies involved relatively small numbers of participants, used highly specific experimental conditions, and relied on a proposed electrostatic mechanism that has not been widely replicated or independently validated by later researchers. 

Subsequent studies have produced far less dramatic findings. A large 2016 prospective study involving 501 couples in the United States examined whether underwear choice influenced semen quality and fertility outcomes. Researchers evaluated 35 semen quality parameters as well as time-to-pregnancy, conception delay, and infertility.

While some minor differences in individual semen characteristics were observed among men wearing different types of underwear, the researchers found that "no significant differences in time-to-pregnancy, conception delay, or infertility were observed." After statistical adjustments, none of the observed semen-quality differences remained significant. The authors concluded that "the style of the male partner's underwear does not seem to affect a couple's ability to achieve pregnancy." 

More recently, a 2026 narrative review examined the available evidence on underwear choice, scrotal temperature, and male fertility. After reviewing studies published up to April 2025, the authors concluded that underwear choice has been associated with only "modest differences in sperm production parameters" and that findings remain inconsistent. Importantly, they noted that "evidence regarding fabric composition remains limited" and that controlled human studies directly comparing polyester and cotton under normal wearing conditions are lacking. 

The review also revisited the older polyester studies and noted that one small experiment had reported reversible azoospermia among men wearing polyester garments continuously for months. However, the authors stressed that the proposed electrostatic mechanism was "biologically unconventional and has not been independently validated." They further stated that the study's small sample size, continuous-wear design, and unusual experimental conditions "substantially limit generalizability" and that typical daily use of synthetic underwear is unlikely to reproduce those conditions. 

What experts say

Dr Prakrutha S, Consultant - Fertility and Reproductive Medicine at Aster CMI Hospital, Bengaluru, said that the claim largely traces back to a handful of older, small-scale studies and should not be interpreted as definitive evidence that polyester underwear causes sperm counts to fall to zero. 

According to her, some early studies did report reduced sperm production among men wearing polyester garments, but those studies had important limitations, including small sample sizes and study designs that make it difficult to apply the findings to the general population. 

"The claim that wearing 100% polyester underwear can reduce sperm counts to zero mainly comes from a few older studies. Due to significant methodological limitations, these findings are not considered conclusive evidence," she said. 

Dr Prakrutha noted that more recent and higher-quality research has not consistently demonstrated a link between polyester underwear and azoospermia, the complete absence of sperm in semen. Instead, she said, male fertility is influenced by a range of factors, including overall health, lifestyle habits, medical conditions, and heat exposure. 

Discussing the role of polyester specifically, she explained that current evidence does not suggest the fabric itself directly impairs sperm production. 

"Polyester fabric does not appear to directly affect sperm production based on current scientific evidence. Factors such as increased scrotal temperature, tight-fitting clothing, prolonged sitting, and exposure to excessive heat are more relevant when it comes to male fertility," she said. 

She explained that the testes are located outside the body because sperm production requires temperatures slightly lower than normal body temperature. Prolonged heat exposure can negatively affect sperm count, movement, and quality. 

While some fabrics may retain heat differently, Dr Prakrutha said there is insufficient evidence to conclude that polyester underwear alone causes significant fertility problems. "When evaluating sperm health, experts focus more on overall heat exposure and clothing fit rather than the specific fabric composition," she added. 

Addressing whether switching from polyester to cotton underwear can improve fertility, Dr Prakrutha said any benefits are likely to be modest in healthy individuals. 

"Some studies suggest that loose, breathable underwear such as cotton boxers may slightly improve sperm parameters by helping maintain a cooler scrotal temperature. However, the improvements are generally small and are unlikely to resolve significant fertility issues on their own," she said. 

She emphasised that male fertility is shaped by multiple factors, including age, body weight, diet, smoking, alcohol use, medical conditions, and environmental exposures. "Underwear choice may play a minor role, but it is only one small part of a much larger picture," she said. 

On the claim that any effects are reversible, Dr Prakrutha said sperm production can recover when a temporary factor affecting sperm health is removed, particularly if excessive heat exposure is involved. 

"If reducing heat-related stress improves the environment for sperm production, recovery is certainly possible. However, there is limited evidence showing that simply switching from polyester to cotton underwear leads to major improvements in sperm counts," she said. 

She noted that sperm production is a continuous process that typically takes around two to three months. As a result, any improvements in sperm parameters would generally take several weeks to a few months to become noticeable. 

This story is done in collaboration with First Check, which is the health journalism vertical of DataLEADS