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Do you really have to wash your hands every time you use the bathroom? The definitive answer, according to science

Ever wondered whether you really need to wash your hands every time you use the toilet or urinal? Food scientist and hand washing expert Donald Schaffner says the science of hand hygiene is clear.

  • We've all been taught to
  • Scientific research suggests that washing up after going to the bathroom, especially if you might have feces on your hands, is an effective way to combat infection and illness.
  • In a pinch, even rinsing your hands with cold water helps prevent the
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We all know what we're supposed to do after using the toilet.

But survey after survey (including one in which scientists secretly camped out in bathrooms) have revealed a dirty truth: people don't always wash their hands before they leave the bathroom.

Don Schaffner, a professor of food science at Rutgers, has been studying hand washing for years and says the conventional wisdom shouldn't be ignored.

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Each trip to the restroom is its own unique journey into germ land. So some occasions probably require more washing up than others.

"If you've got diarrhea all over your hands, it's way more important that you wash your hands than if... you didn't get any obvious poop on your fingers," Schaffner said. "My gosh, if you've got poop on your hands and you have the time, certainly, get in there, lather up real good and do a real good job."

But it's best to wash your hands after every trip to the toilet because human feces carry pathogens like E. coli, Shigella, Streptococcus, hepatitis A and E, and more.

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Religious traditions have urged cleanliness via ritual hand washing for thousands of years. But it wasn't until the 1800s that health care professionals linked good hand hygiene to lower infection rates.

Dr. Ignaz Semmelweis noticed that when doctors and medical students handled cadavers before touching patients in the maternity ward, more mothers developed fevers and even died. He instituted an unpopular chlorine-washing rule and saw the death rates tumble.

Similarly, during the Crimean War, nurse Florence Nightingale initiated hand-washing rules and other hygiene measures in the British hospital where she worked. Death rates there dropped by two-thirds, providing some of the first hard evidence that proper hygiene saves lives.

We're still far from perfect at preventing infections.

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We all come in contact with unsavory substances regularly, especially after touching public doorknobs, our cell phones, and moist kitchen towels — all of which are likely dirtier than a clean toilet seat, which typically houses just 50 bacteria per square inch. So hand washing at any time of day can help stop the spread of many kinds of bacteria, yeasts, and viruses.

"I think a good general rule of thumb is you should wash your hands any time you feel that they might be dirty," Schaffner said. In other words, seize the opportunity when you're near a sink.

He said he's not "super paranoid" about making sure his own hands are always squeaky clean, but some of his favorite times of day to wash up are after walking the dog, working in the dirt, or handling raw meat.

Even a quick "splash ’n dash," as researchers like to call the practice of rinsing with water but no soap, can help fight off some bacteria that causes infections. But that shortcut is not advised if you might have raw meat or feces on your mitts, and a lather with soap and water is more effective at disinfecting hands than any wipe or sanitizer.

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Follow this simple, three-step hand-washing plan to lower your chances of getting colds, self-inflicted food poisoning, and diarrhea.

First, don't worry about the temperature of the water; Schaffner's studies have confirmed that doesn't make a difference. He suggests that you "adjust the water temperature so it's a nice comfortable temperature, so you can do a good job."

Second, give yourself enough time to "get some soap in there, lather it up real good, clean under your finger nails," Schaffner said. Spending even five seconds washing your hands can help reduce the amount of bacteria on them, but 20 seconds is better. The Centers for Disease Control recommends humming the Happy Birthday song to yourself twice as a timer.

Third, dry off before you leave the room. This step is key because wet hands transfer more bacteria than dry ones.

"If your hands are still wet, you go to touch that door of the bathroom, having your wet hand might actually help transfer bacteria," Schaffner said. He'll even dry his palms on his pants if there's no paper towel around.

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Despite all the evidence demonstrating the health benefits of regular hand washing, Schaffner knows his advice can only go so far.

"I'm not in charge of you washing your hands, just because I'm a guy who did some science and did some research on hand-washing," he said. "You do what you want."

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