August 8, 2018

expert reaction to study looking at men’s underwear type and semen quality

A new study, published in Human Reproduction, examines the association between type of underwear worn and markers of testicular function among men attending a fertility centre.

Prof Richard Sharpe, Honorary Professor, MRC Centre for Reproductive Health, University of Edinburgh, said:

“Successful sperm production requires a temperature 3-4°C below core body temperature and this is achieved via a specialised blood cooling system and placement of the testes outside of the body in the scrotum.  It is well established that anything that interferes with maintenance of testes cooling is likely to impair sperm production/quality.  The extent to which type of underwear worn might cause such interference has been a subject of debate for many years.

“The present quite large study provides reasonably strong supporting evidence that wearing of tighter underwear might cause mild, but significant, impairment of sperm production in men.  However, it is an association study, relies on self-reporting (of underwear type) and is restricted to males attending an infertility clinic, all of which urge us to be cautious when interpreting the findings.  Nevertheless, the study adds to the evidence that in couples trying for a baby, wearing of looser underwear (and trousers/jeans) and avoiding other sources of scrotal heating such as hot baths and saunas are easy lifestyle adjustments for the man to take that might have a positive effect on his sperm count/quality.  In turn, this my increase the chances of the couple achieving a pregnancy – although pregnancy success was not measured in this study so we don’t know whether these sperm quality changes affect fertility.

“What is not explored in this study is whether occupation of the men and the time that they spend seated were also important, as it is established that modern sedentary lifestyles/occupation are associated, like wearing of tight underwear, with increase in scrotal temperature.  It might be predicted that men who spend much of their day seated and also wear tight underwear would be most likely to suffer a fall in their sperm production due to scrotal heating.

“Unfortunately, we have few if any treatments for improving sperm count/quality and male fertility, but adopting a lifestyle that maintains a cool scrotum (temperature-wise) is one easy change that men can make that can only be beneficial, and which has no side-effects.  The present study provides further reason for men to take note of this.”

Prof Sheena Lewis, Emeritus Professor of Reproductive Medicine, Queen’s University Belfast, said:

“The most important take home message from this study is that neither boxer shorts, jockeys nor bikinis led to a drop in sperm counts below the normal range.  There are also a number of confounding factors in the study because the group wearing boxer shorts were more likely to be younger, slimmer men but they also subjected their testes to higher temperatures by enjoying hot baths or Jacuzzis and wearing skinny jeans on top of their loose underwear.  I would also question the use of underwear type as a scientific way of measuring scrotal heat.  We aren’t told what ‘frequently’ means in terms of their underwear use – how many hours a day, how many days a week – but actually it doesn’t really matter since none of the underwear types being investigated caused a problem.”

Prof Allan Pacey, Professor of Andrology, University of Sheffield, said:

“This is an interesting study which evaluates whether semen quality of men attending a fertility clinic is correlated with the type of underwear they report wearing.  Whilst this may seem a relatively simple question, it is one where we have conflicting data and so this study is a useful addition to the evidence base.

“In summary, the results of the study show that in comparison to men who report wearing tight underwear, those who wear loose (boxer style) ones generally ejaculate semen samples with higher sperm concentrations, higher total sperm counts and a higher number of motile sperm.  However, these results are not a surprise to me and essentially confirm the results from the 2,249 UK men enrolled in the CHAPS-UK study which we published in 2012.  This showed that the men who wore boxer shorts were significantly less likely to have low motile sperm counts and in a further paper in 2014, we showed that type of underwear was unrelated to sperm morphology (a measure of sperm size and shape) which the authors also confirm in this study.

“In comparison to the CHAPS-UK study, however, these authors have gone further by reporting in a subset of men measurements of the reproductive hormone FSH, as well as the measurement of sperm DNA fragmentation using the COMET assay.  Interestingly, although sperm DNA fragmentation did not show any correlation with type of underwear, the measurements of FSH were higher in men who wore tight underwear (and therefore also had poorer sperm quality).  This is an intriguing observation as it implies that the wearing of tight underwear may be damaging the testicles in some way (and is why the FSH levels from the pituitary rise to try and make the testicles work harder at producing sperm).

“This study confirms my long-held belief that men with poor sperm quality could potentially improve things by wearing looser underwear and keeping their testicles as cool as possible.  However, we should recognise that neither this study (nor the CHAPS study) were randomised controlled trials.  Therefore, there is no actual proof that switching underwear style will make any difference.  However, I think it is a reasonable low cost and low risk lifestyle change that men with poor sperm quality can undertake to potentially improve their semen quality.  It’s also important to note the study is not implying underpants are a major cause of infertility – in fact, fertility has not been measured.  There is a big difference between measuring aspects of sperm quality (as done in this study) and measuring fertility.”

Dr Richard Quinton, Consultant and Senior lecturer in endocrinology, Royal Victoria Infirmary and Newcastle University, said:

“Scrotal temperature in humans is typically 2.5-3°C lower than core body temperature (37°C) and spermatogenesis is most efficient at 34°C.  That’s why the testes hang down away from the body and have their own special blood cooling system, the pampiniform plexus.  So, based more on common sense first principles and small uncontrolled reports, it’s been standard advice given to men in fertility clinics throughout the world that they wear loose fitting underwear and avoid taking hot baths.

“This study validates some of this advice in a much more rigorous and evidence-based manner.  Hot baths and saunas don’t appear to be an issue, presumably because only a tiny proportion of one’s time is spend in these activities, but tighter underwear really does have a significant association with reduced sperm count and quality.  Moreover, this study also found that tighter underwear and lower sperm count and quality were associated with higher levels of the pituitary hormone, FSH.  FSH (in conjunction with locally secreted testosterone) acts on the Sertoli cells in the testes to promote and maintain spermatogenesis.  When Sertoli cell function or number begins to fail, this is detected by the pituitary gland through a fall in blood levels of Inhibin B (hormone secreted by healthy Sertoli cells).  The pituitary gland then responds by increasing secretion of FSH in an attempt to support the ‘failing’ Sertoli cells.”

Prof Ashley Grossman, Professor of Endocrinology at Oxford Centre for Diabetes, Endocrinology and Metabolism, said:

“This appears to be high quality research which extends anecdotal and previous less well-controlled reports that a high scrotal temperature, secondary to tight underpants, may contribute to a lower sperm count and quality.  It appears to have controlled for ‘confounding factors’, and adds useful clinical information.  Men could be advised to wear boxer shorts, a simple measure.

“The men studied were partners of women undergoing fertility investigation, so not far off a ‘normal’ population.  Although the sample size was large, the differences are small but then it only takes one sperm to fertilise an egg, so these are still significant findings. Of course, since so many sperm are produced per ejaculate and the results are generally within the normal range, it is difficult to know if these minor changes are significant in terms of fertility.  However, it is a simple measure to wear boxer shorts when there is uncertainty regarding fertility, so where there is concern it is worthwhile considering this type of change in lifestyle.  However, we do not know whether looser pants actually cause the increased sperm numbers and quality, and therefore whether they would be likely to improve actual fertility.”

* ‘Type of underwear worn and markers of testicular function among men attending a fertility center’ by Lidia Mínguez-Alarcón et al. published in Human Reproduction on Wednesday 8 August 2018.

Declared interests

Prof Richard Sharpe: “I have no conflicts of interest to declare.”

Prof Sheena Lewis: “Sheena is CEO of SpermComet Ltd, a university spin-out company marketing a test for male infertility: www.spermcomet.com.”

Prof Allan Pacey: “Chairman of the advisory committee of the UK National External Quality Assurance Schemes in Andrology, Editor in Chief of Human Fertility and Trustee of the Progress Educational Trust (all unpaid).  Also, recent work for the World Health Organisation, British Broadcasting Corporation, Purple Orchid Pharma (paid consultancy with all monies going to University of Sheffield).  Co-applicant on a research grant from the Medical Research Council (ref: MR/M010473/1).”

Dr Richard Quinton: “No conflicts to declare.”

Prof Ashley Grossman: “No conflicts to declare.”