Don’t bother, says Stephen Craig Cary, a University of Delaware expert on frozen microbes, who wrote to us from Antarctica.
Most of the bacteria on your jeans probably started off on your own body. Since these critters are happiest living at the temperature of human skin, “one might think that if the temperature drops well below the human body temperature they will not survive,” Cary writes, “but actually many will. Many are preadapted to survive low temperatures.” And it takes only one survivor to repopulate your jeans when they warm up.
“I would suggest that you either raise the temperature to 121 degrees Celsius for at least 10 minutes,” Cary writes, “or just wash them! The latter surely is the best alternative to save energy.”
Julie Segre of the National Human Genome Research Institute, who studies the skin’s microbiome, seconds the washing recommendation. “The bacteria that would live on your jeans on the sloughed skin and the dirt nutrients than the jeans themselves, so detaching the sloughed skin could reduce the microbial load of your jeans,” she says. In her opinion, removing the dirt and the sloughed skin is more important than removing any bacteria, though she warns that she may have “just transitioned from speaking as a scientist to speaking as a mother.”
How often you wash your jeans may depend on how comfortable you are with the growing amount of dirt and sloughed skin on the fabric; the bacterial load doesn’t seem to be much affected by how often you go between washings. A somewhat unscientific experiment by a Canadian student found little difference in the bacterial load between one pair of jeans worn for 15 months without washing and another pair worn for 13 days.
So, sorry Levi’s, freezing our jeans sounded like a great idea, but it’s probably not doing anything more than taking up space better left for ice cream.