If you’ve ever had athlete’s foot, you know how hard it is to get rid of. Its persistence is not a reflection of its victims’ athletic abilities, but rather a testament to the strength of the fungi that cause this common and highly contagious condition, also known as tinea pedis.

Why is it so tough to make this fungal infection go away and not come back? A new study suggests a surprising reason—you may be inadvertently reinfecting yourself by doing your laundry wrong! Worse, you’re putting more than just the skin of your feet at risk—because the same fungi responsible for athlete’s foot also can spread, bringing on toenail infections (tinea unguium) and jock itch (tinea cruris). Here’s what your laundry has to do with the unsightly scaling and unbearable itching…


For the new study, Israeli researchers got hold of 81 people with confirmed cases of athlete’s foot or toenail infection—and asked them to donate their dirty socks! That’s right…the volunteers wore their socks for at least six hours, then turned the socks over to the researchers. Next, each sock was snipped up to produce fabric samples, three from the toe area and three from the heel. Of the three toe/heel fabric sample pairs from each sock, one pair was cultured in a lab to identify the pathogens it harbored…a second pair was washed at 104°F (40°Celcius), which is a typical warm-water setting…and the third pair was washed at 140°F (60°Celcius), which is a typical hot-water setting. A residential-type washing machine and detergent were used (nothing industrial or unusual).

Then all the fabric samples were cultured to look for any signs of remaining fungus. Gross findings…

Of the unwashed sock samples, 85% tested positive for fungus—showing that fungi can indeed be transferred from feet to fabric.

Of the sock samples washed at 140°F, only 6% tested positive for fungus after laundering, meaning that the hot water did a good job of killing off fungi.

Of the sock samples washed at 104°F, however, post-laundering analysis showed that 36% still tested positive—so the warm water, even with detergent, was not effective at eradicating fungus. Furthermore, there was evidence that fungi actually spread from contaminated patches of fabric to previously uncontaminated patches of fabric during the warm-water wash—which suggests that a contaminated sock could spread your foot infection around to the rest of the clothes in that load of laundry!

Laundry lesson: Yes, we all want to save energy—but skimping on the hot-water wash isn’t the way to go to fight athlete’s foot, toenail fungus and jock itch. Warm water just won’t cut it because it’s barely above body temperature…and we already know how well fungi thrive in that condition. Problem is, in the US, household water heaters typically are set to 120°F to minimize the risk of scalding. Solutions: If you are prone to recurrent fungal infections, you could set your water heater to 140°F (and then take care not to scald yourself while using a sink, shower or tub). Or if you have a top-loading washing machine, you could (carefully!) pour in a kettleful of boiling water once the machine has filled. Or you could get a washing machine that further heats the water itself (such as the Whirlpool Front-Load Washer with Deep Clean Steam, Model #WFW86HEBW, which can get the water up to 150°F).

What about the dryer? This study did not look at the effects of drying fungi-contaminated socks in a clothes dryer, so we can’t say how a dryer’s heat might have affected the results. However, many clothes dryers may not get hot enough to kill off fungi (for instance, according to GE, its high heat setting is 135°F)…and even if your dryer is hotter, researchers didn’t examine how long a drying cycle might be needed to destroy fungi. One thing we do know, though, is that no matter whether you line-dry or use a clothes dryer, dark and moist environments are fungi-friendly—so make sure that your socks and underwear get thoroughly dried before you put them away in a drawer.