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According to a new survey conducted by apparel maker Tommy John, nearly half of Americans polled don't change their underwear every day. 13% of Americans say they wear the same underwear for a week or longer!

Of the 1,000 people responding to the informal poll, 45% of men and women admitted they wore the same pair of dirty underwear for two or more days, Tommy John said.

Some people sniff their underwear to determine whether it's clean enough to wear again. Excuses for wearing the same undies daily include economic and cultural factors.

"Conventional wisdom — and basic common sense — tells us that we should change our underwear every day, or at least wash them after every wear," Tommy John said in a statement. "After surveying 1,000 Americans, we found that this basic standard of underwear hygiene is definitely not universal."

Tommy John said men were 2.5 times as likely as women to wear unwashed undies for a week or more. That’s 20% of men versus 8% of women.

NYU microbiology and pathology professor Philip Tierno says wearing the same underwear every day is not a measure of good hygiene. Even after you wash your underwear, bacteria is still clinging to them.

No matter how much you try to wash it away from your skin, you can't really get rid of it all, Tierno told Huffington Post last year.

"But it's normal, and it doesn't hurt you," Tierno added.

He advised against wearing the same underwear for longer than 2 days.

There's roughly a 10th of a gram of feces on your underwear after every wash, according to Dr. Charles Gerba, a professor of microbiology at the University of Arizona.

The best way to wash your undies is in the hot water cycle with bleach, which is the most effective product to kill the organisms living on your undies, Tierno said.

Or you can do what some wealthy socialites do and throw your undies away after every wear.