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Dear Mona, How Often Should I Change My Socks?

Dear Mona,

More Science & Health

How long can I wear the same pair of socks without health risk? I wear them until the smell offends me. Am I wrong?
@thomasasma


Dear @thomasasma,

Last week it was peeing in the shower, this week it’s re-wearing socks. It seems like you guys really care about your (statistical understanding of) personal hygiene.

The American Podiatric Medical Association lists 21 common foot conditions. Many of them, such as hammertoe and arthritis, won’t be affected by how many times you wear your socks. The same can’t be said of ailments that are related to the presence of microorganisms.

Athlete’s foot, a fungal infection, is one example. And it’s a prevalent one, too — at any given time, 15 to 25 percent of people have it (the first reported case in the United States was in a WWI veteran in the early 1920s in Birmingham, Alabama). Also known as tinea pedis, or ringworm of the foot, the condition can spread to other parts of the body, so it can also be the cause of tinea cruris, or ringworm of the groin, aka “jock itch.”

One way to avoid athlete’s foot, tested by the U.S. military, is to wear sandals. A 1944 study gave 2,100 servicemen sandals and found that foot infection rates fell from 81 percent to 3.5 percent. The researchers also found that “the men, for the most part, liked the sandals.”

But winter’s coming. So you might prefer another method to avoid fungal infections: Regularly change your socks.

If the risk of an itchy groin isn’t enough to persuade you to put your socks through a spin cycle, let’s talk about foot odor. Your doctor might call it bromidrosis pedum, but your friends and lovers are more likely to say it like they smell it: B.O. of the foot.

I don’t know about you Americans, but the U.K.’s National Health Service wisely suggests that you treat your feet to a clean pair of socks at least once a day to avoid smells. Fabric matters, too. A study released this month by scientists at Ghent University in Belgium took the T-shirts that 26 individuals had been wearing during an hourlong spinning class, let the shirts stew for 28 hours and then gave them to a “trained odor panel.” Bacteria was more likely to sit on the surface of polyester than on cotton and, as a result, shirts made of artificial fabric smelled worse.

Their research (and your subsequent tweets about jeans and bacteria) got me thinking about other types of clothing. Even the American Cleaning Institute (ACI), a body that represents the U.S. Cleaning Products Industry, doesn’t recommend daily changes of all your clothing. While socks, underwear, T-shirts and tank tops should be washed after each use, the ACI advises that “pajamas should be washed after 3 or 4 wears,” “bras can be worn 2-3 times” and “jeans can typically be worn 3 times before washing.”

Josh Le might think that’s an underestimate. As you pointed out, while Le was a student at the University of Alberta in 2009, he wore the same pair of jeans every day (and occasionally as nightwear) for 15 months and one week. At the end of it, his professor Rachel McQueen, an expert in textile science, took bacterial counts from the trousers — a test she repeated two weeks after the jeans had been washed and concluded that “bacteria growth is no higher if the jeans aren’t washed regularly.”

Typical behavior of Americans might not be that extreme. A 2011 survey of the laundry habits of 1,200 American adults by Clorox (which, as a manufacturer of cleaning products, could have an interest in encouraging more detergent use) found that about 13 percent of men wear their underwear two or three times between washes. Clorox also claims that “younger men (under 29) and older men (over 50) are more likely to wear jeans four or five times before washing.” So, if you’re asking me the question because you don’t change your clothes too often, you’re certainly not alone. Nevertheless @thomasasma, my simple advice would be to keep it fresh.

Hope the numbers help,

Mona

Have a question you would like answered here? Send it to dearmona@fivethirtyeight.com or @DataLab538.

Mona Chalabi is data editor at the Guardian US, and a columnist at New York Magazine. She was previously a lead news writer for FiveThirtyEight.

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