Does washing clothes kill all the germs?


Laundry serves far nobler purposes than stamping out body odor. It also protects you from getting sick. (Brace yourself, because this is going to get gross in a hurry.)

Imagine that someone who lives in your house is ill. A single gram of his fecal matter contains millions of viruses, and exposure to just a hundred of those viruses can make you sick, says Kelly Reynolds, a germ researcher and associate professor of environmental health at the University of Arizona.

Regardless of how assiduously he wipes, the average person has about a tenth of a gram of fecal residue in his underwear, says Chuck Gerba, a professor of microbiology at Arizona. If you’re washing that sick person’s underwear with your own, chances are very good that his sickness-causing organisms are going to make their way onto your clothing.

“We’ve found that one germy item in the washer will spread to 90% of the other items,” Reynolds says. And no, it doesn’t matter how hot you set the water temperature on your machine. “When it comes to molds that cause skin or respiratory infections, or organisms that cause colds, flu and stomach flu, most of them will survive the wash cycle,” she says.

It’s the dryer—not the washing machine—that lays waste to harmful microorganisms. “High heat drying for at least 28 minutes is the most effective way to kill viruses,” Reynolds says. The “high heat” setting is key. Energy efficient, low-heat settings may not get the job done, she says.

You’re not even safe if you wash your sick housemate’s clothing separately from your own, since his germs will hang out in the washer even after the clothing is gone. Run a wash cycle with bleach or another type of disinfectant to clean it of sickness-cause organisms, Reynolds says.

The good news is that if no one in your household is sick, you can relax a bit about killing the germs in your load. “It’s when someone is ill that you really want to up your game,” Reynolds says. If your housemate catches something, have him or her wear clothing and sleep on sheets that you can wash and dry using high heat.

And yes—it’s ok to spare your expensive, line-dry only gym gear from the dryer. Your big worry there is probably foul odors, not viral pathogens. If you’re diligent about washing your hands (and wiping down the machines at the gym before you climb aboard) you shouldn’t have much to worry about, Reynolds says. Just be sure to wash your duds soon after you finish exercising. “The longer those clothes remain damp with sweat, the more mold and bacteria are going to proliferate,” she says.

If your first instinct after reading this is to double down on detergent, don’t. A washing machine’s cycles are designed to break up and wash away only so much cleaning agent, says Jolie Kerr, an author, cleaning expert and host of the podcast Ask a Clean Person. If you have a heavy hand with the pump or scoop, the excess detergent can build up on your clothing and lock in bacteria and odors, she says. (Fabric softener, too, can coat your clothing in a residue that traps smells, she adds.)

If you can’t dry your stuff on high heat—or at all—hang it up outdoors or in direct sunlight. The sun’s ultraviolet light has disinfecting properties, Reynolds says.

Finally, be mindful of transferring your clothes from the washer to the dryer. “Unless you’ve used bleach or some other disinfectant, those items are not sanitized,” Reynolds says, so be sure to wash your hands after handling them.

Thanks to Mr. C for bringing this to the It’s Interesting commmunity.

Scientific testing of the ‘5 second rule’ of food on the floor

The five-second rule is based on the not-entirely-scientific belief that bacteria cannot contaminate food within five seconds, so you won’t get sick eating things you have picked up from the floor.

The first person to investigate this urban myth scientifically was Jillian Clarke, an American high-school student, during an apprenticeship in a microbiology laboratory at the University of Illinois in 2003. Clarke and her colleagues inoculated rough and smooth tiles with the bacterium E coli (certain strains of which cause stomach cramps, diarrhoea and vomiting) and put gummy bears or cookies on the tiles for five seconds. She found that E coli was transferred to gummy bears within five seconds, more so from smooth than rough tiles. As a side issue, Clarke also established in her work that university floors are remarkably clean and that people are more likely to pick up cookies from the floor than cauliflower.

Paul Dawson, professor of food science at Clemson University in South Carolina is a five-second-rule expert. His 2007 study, published in the Journal of Applied Microbiology, found that the dirtiness of the floor was more important than how long the food lay on it. His study was a progression from Clarke’s because it measured the amount of contamination. Using bread or bologna, he showed that it was better to drop either of them on carpet inoculated with salmonella, where less than 1% of the bacteria were transferred, than on tiles or wood, where up to 70% got on to the food. A similar study from Aston University found that, as soon as food hit the floor, it became contaminated – especially on smooth surfaces – but that the number of bacteria on the food increased up to 10 times between lying from three seconds to 30 seconds on the floor.

Dawson says that the five-second rule is simply not true because, if food hits a virulent brand of E coli, even the small number of bacteria it attracts immediately will make you sick. He doesn’t eat food when it falls on the floor. The very young or old shouldn’t use the five-second rule as their immune systems may not cope with even tiny amounts of bacteria. If the floor is filthy, then the rule is invalid on the grounds of grossness anyway. But the likelihood is that, for most of us, eating food off the floor isn’t going to hurt us. So if you are very hungry and you must pick food off the floor, then do it quickly, and preferably off a carpet.