The argument for not washing your jeans has traditionally been about making your denim last longer. Hot water and detergent can speed up how quickly your jeans fade. Bergh also sees it from an environmental perspective. Not washing your jeans saves water and energy, a message that's part of the company's focus on building sustainability.

But is it safe?

There is no evidence that not washing jeans is hazardous to your health, said Bernhard Redl, an associate professor in the molecular biology department at the University of Innsbruck in Austria. That is, when they are worn under normal conditions, such as everyday street wear.

Bacteria, skin cells, and sweat are transferred to our pants from our own body but "skin microorganisms are generally not hazardous to ourselves," said Rachel McQueen, a professor of human ecology at the University of Alberta in Canada. McQueen's research focuses on the development and retention of odors in textiles.

"There are environments where having sterile clothing is important," McQueen said. That would be true in a hospital, for example, where clothing can transfer infections. "However," she added, "sanitizing your hands is going to be a more important issue here than washing your jeans."

A few years ago, one of McQueen's students wore his jeans for 15 months straight without a single wash and then tested the level of bacteria on them. The student-teacher team was surprised to find that the unwashed jeans carried nearly the same amount of bacteria as those same pants after they had been washed and then worn for another 13 days.

"What I found was just normal skin flora," McQueen told the National Post in 2011. "The counts were really, really similar. The bacteria load from the swabbed areas were pretty much the same."

The Freezing Myth

Although not laundering your jeans doesn't seem to pose any health risks, the smell could become a problem (for you and those around you). Denim-heads have suggested freezing your jeans as a way to kill bacteria and the stench, although there's no scientific proof that this method is effective.

"It is clear that freezing does not kill most of the bacteria," said Redl, "but puts them in a dormant state." Bacteria stops growing in the freezer, but will become active again once you slip your pants back on and those germs are warmed up by the heat of your body.

"I think airing your jeans outdoors in the sunlight would be a more effective method of getting rid of odors and a lot of bacteria," said McQueen.