Here's what happens if you never wash your jeans

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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.

Levi's CEO Chip Bergh says we should stop washing our jeans because it's good for the environment since it saves water and energy.

"If you talk to real denim aficionados, they tell you don't wash your blue jeans," Bergh said in a 2014 interview at Fortune magazine's Brainstorm Green conference.

This advice may seem cringeworthy. But apart from smelling, microbiologists say there is nothing to worry about from a health perspective if you never wash your jeans.

Is not washing your jeans safe?

There is no evidence that not washing jeans is hazardous to your health, according to Bernhard Redl, an associate professor in the molecular biology department at the University of Innsbruck in Austria. This generally holds true when your denim is 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, "sanitizing your hands is going to be a more important issue here than washing your jeans," she said.

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 washing your jeans doesn't seem to pose any health risks, the smell could become a problem. Denim-heads have suggested freezing your jeans as a way to kill bacteria and the stench, although there is 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.

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