A Harvard-trained doctor has suggested that vaping could be causing men's sperm count to collapse.
Dr Saurabh Sethi, a gastroenterologist in San Francisco, claimed that chemicals in the devices can enter the blood and travel to the testes.
Once there, he said they could cause sperm cells to die or damage the swimmers and the DNA that they are carrying — harming a man's fertility.
Sperm counts have been in free-fall for decades, in a downturn that experts say now 'threatens mankind's survival'.
Dr Saurabh Sethi, a gastroenterologist in San Francisco, warned online that chemicals in the devices can enter the blood and travel to the testes (Above, grabs from his TikTok)
In 1973, studies suggest the average ejaculate contained about 101.2million sperm per milliliter (million/mL) of semen.
But by 2018, they had more than halved to just 49 million/mL.
There is no concrete evidence linking vapes to falling sperm counts, however, with experts instead blaming other factors including bulging waistlines.
Dr David Shusterman, a urologist in New York City, said: 'I would recommend that people do not vape, but that is not because of any impact on sperm count — but rather the other health problems associated with it.'
He added: 'Everyone seems to think that anything can cause decreased sperm count, and in reality the main thing is people's lifestyle.'
He said other factors were more likely to be driving low sperm counts including people exercising less and eating a diet packed with ultra-processed foods.
Age could also be involved, with studies showing that a man's sperm count dropping by up to three percent annually from the age of 40 years.
Previous studies have warned that smoking slashes a man's sperm count because of the toxic substances released by its combustion fire — or what happens when something burns.
In a TikTok video, he revealed three things that he said could be slashing a man's fertility
Vapes do not use the same combustion fire, instead relying on atomisation — when a liquid is broken down into very fine droplets or mist — meaning they do not release the same toxic substances.
Speaking in the clip on TikTok posted to his 364,000-follower audience, Dr Sethi said: 'Vaping introduces chemicals like propylene glycol, which has been linked to decreased sperm quality and motility [movement],' he said.
'These chemicals can cause oxidative stress which can affect your fertility.'
Men are more likely to vape than women, with a CDC survey estimating that about 5.1 percent of men over 18 years old are current e-cigarette users.
But younger men are much more likely to use the devices, with rates doubling to 11.6 percent in the 18 to 24 age range.
The concerns over e-cigarettes and fertility add to the growing list of health issues linked to the devices, which also includes a higher risk of suffering from lung cancer, lung damage and heart disease.
In his video, Dr Sethi revealed his top three 'male fertility killers'.
The other two he named were sitting in hot saunas and stashing a cellphone in a frontpocket — saying both could harm a man's sperm count.
He said: 'High temperatures from hot tubs and saunas can lower sperm count and quality because the testicles need cooler temperatures to produce healthy sperm.
'A single prolonged exposure can impact sperm production for up to three months.
'Second... research shows that carrying your cellphone in your front pocket can reduce the sperm count and motility due to electromagnetic radiation.'
Some studies have suggested that saunas can reduce sperm counts because they cause heat stress to testicles, with their average temperature of around 155 to 195F is well-above the 93.2F needed for generating healthy sperm.
But male fertility researchers and urologists have previously said this should only be a concern for someone who does these exercises regularly.
Previous studies have also suggested that mobile phones could damage sperm count because the heat produced by the devices could cause heat stress to the testicles.
But in recent decades as new technologies have come in the power output from phones has dropped, vastly reducing this risk.
Previous studies have also not found a consistent link between where a phone is stashed on someone's person and their sperm quality.
Other experts say that these claims have already been 'debunked'.
Dr Sethi regularly posts health tips online to his followers on TikTok as well as other social media platforms including Instagram and YouTube.
