If you believe your mom, the answer is “every time you wear them.” But if you believe Chip Bergh, CEO of Levi Strauss & Co., the answer is “never.”

Bergh’s reasons are complicated—they have more to do with environmentalism than good hygiene—but he insists it can be done.

And what about that daily dirt? Bergh suggests spot cleaning, or even putting jeans in the freezer once a month to kill off bacteria. Opinion is divided on whether this is a good idea. Some experts say that many bacteria have pre-adapted to survive such temperatures. (Others would advise you not to store your jeans next to microwave burritos.)

But there is a happy middle ground, we say, as does Joyce Sobczyk, a stylist and owner of the Closet Consult in Florida, who suggests washing jeans at least three times a year—unless you’re a guy who goes commando. “That’s a different story,” says Sobczyk. “Then you have to ask yourself, ‘How often would I wash my underwear?’