Men often joke that cold weather is to blame for a less-than-impressive bulge.

But scorching summer heat might not be such a blessing either.

Specialists caution that the phenomenon known as ‘summer long balls’—where penises and testicles seem larger and hang lower due to hot weather—might actually pose risks to fertility.

The effect, seen during last week’s 33.6C heatwave in Britain, is the body’s natural reaction to rising temperatures.

Dr. Anika Ackermann, a certified urologist, informed The Cut, ‘In colder conditions, the testicles retract towards the body, and the scrotum tightens up.’

‘The opposite is true in a warm environment. The scrotum relaxes, and the testicles move away from the body.’

This movement is intended to safeguard sperm. The scrotum, or scrotal sac, functions like a thermostat, adjusting the proximity of the testes to the body to prevent them from overheating or getting too cold.

While this temporary reaction can affect sperm production, experts stress it does not cause lasting damage to fertility.

Many men may notice temporary adjustments in the size and position of their penis and testicles with changing weather. However, for some, this could severely impact their fertility.

However, according to leading urologist Dr Yaniv Larish, this phenomenon can also be caused by varicoceles, or enlarged veins in the scrotum. 

‘In cases of varicocele, the blood does not circulate efficiently, so rather than cooling the testicle by circulating, it collects and insulates the testicle at a higher temperature,’ he elaborated.

According to John Hopkins Medicine, the condition is very common affecting around 15 percent of adult men. 

Whilst for most varicocele will go unnoticed, Dr Larish said the condition can become ‘more pronounced’ in warmer weather.

This can cause a number of issues including reduced fertility, decreased testosterone and scrotal discomfort. 

Nevertheless, experts state that while warm weather can greatly reduce fertility and adversely affect sperm quality, the impact is generally temporary in most instances.

However, in men with varicoceles, fertility could be an issue—though this is a vehemently contested theory. 

One purported theory is that varicoceles can interfere with the body’s ability to make and store sperm but research on whether treating varicoceles cann improve fertility is mixed. 

While the WHO estimates one in six adults globally will be affected by infertility in their life time there are regional variations

Either way, whilst there is no hard and fast cure for ‘summer long balls’, experts say there are a few things you can do to reduce discomfort. 

Dr Ackerman recommends wearing tighter underwear for scrotal support and spending as much time in cooler environments as possible. 

And if you don’t have an air-conditioned space to take refuge in, the urologist suggested investing in a pair of ‘Nutsicles’—essentially an ice pack for testicles primarily marketed at vasectomy patients—to keep cool all summer long. 

The warning comes as research finds just a one degree increase in ambient temperature can lead to a drop in sperm production.

The study, published recently in the journal Biomedical and Environmental Sciences and reported last week by the Daily Mail, analysed semen samples from more than 6,600 donors worldwide over a six-year period.

On average, the mercury reached highs of between 6.7C (44F) and 18.2C (64.8F) across the nations sampled—with the highest being 42.1C (107.8F).

And the results showed those living in hotter climes had less sperm motility—the ability of the cells to move effectively, which is crucial for successful fertilisation.  

Experts are calling for all men to be regularly monitoring their sperm from their late teens onwards in a bid to identify thousands of hidden cases of male infertility at an earlier stage. 

Research suggests male infertility is a factor in about half of all cases where couples fail to conceive.

Yet many cases could be identified and potentially treated early if every man had a semen analysis when they turned 18 and again a couple of years later to monitor changes in sperm count and motility, argues Tet Yap, a consultant andrological surgeon at Guy’s and St Thomas’ NHS Foundation Trust and the private Princess Grace Hospital, both in London.