The CEO of Levi’s has swirled up the debate around how often you should wash your jeans once again. His theory, in sum: you should avoid putting your jeans in the washing machine at all costs and only spot-clean parts that are affected by stains when needed.

Back in 2014, it was widely reported that Levi’s chief Charles Bergh told denim enthusiasts that they should never ever wash their jeans. In a new interview, he clarified these comments – and delivered some peculiar advice about showering in your jeans.

“I never said don’t wash your jeans,” Bergh told CNBC. 

“True denim heads, people that really love their denim, will tell you to never put your denim into a washing machine. So that’s what I do,” he added.

“If I drop some curry on my jeans, I’m gonna clean it. But I’ll spot clean it. And if they get really gross you know, if I’ve been out sweating or something and they get really gross, I’ll wash them in the shower,” he said.

Bergh argues that washing jeans is a major part of the clothing’s carbon footprint. As per Oxfam, each pair of jeans creates around 33.4 kilograms (73.6 pounds) of carbon dioxide – comparable to flying a plane around the globe 2,372 times. It also takes an estimated 1,800 gallons of water to produce the cotton in a pair of jeans. 

To dampen the impact of denim on the planet, the Levi’s boss believes consumers should avoid putting their jeans in the washing machine. Heating the water and powering the machines requires huge amounts of energy, with the average load of laundry releasing 3.3 kilograms (7.2 pounds) of carbon dioxide.

This might sound a bit gross, but there’s actually some evidence to suggest that jeans remain remarkably clean without washing. 

In 2011, researchers at the University of Alberta carried out an experiment using one of their student’s dirty jeans. Josh Le didn’t wash his raw denim jeans for 15 months then swabbed them for bacteria. He then put the pants through a washing machine, wore them for another two weeks, and re-tested them.

Remarkably, the levels of bacteria didn’t vary that significantly. The jeans were more or less just as clean after two weeks of wear as they were after 15 months of no washes. 

"I expected to find some bacteria associated with the lower intestine such as E. coli, but was surprised to find there weren't any, just lots of normal skin bacteria," Rachael McQueen, an Associate Professor at the University of Alberta who carried out the research, said in a statement. 

"This shows that, in this case at least, the bacteria growth is no higher if the jeans aren't washed regularly," she added.