It has long been supposed that hot water works to get bacteria off your hands better than cold water. But the hot water needed to kill bacteria is way too hot to be comfortable to use when washing your hands.
Luckily, studies have proven that hot water is not necessary to use while hand washing. In fact, a new study published in the Journal of Food Protection found that cool water is just as effective at removing bacteria in handwashing as hot water. More than 20 participants were tracked for six months and instructed to wash their hands in 60, 79 and 100 degree water using varying amounts of soap. Researchers found the 60-degree water cleaned hands just as well as the hot water.
And in a 2005 study documented in the Journal of Occupational and Environmental Medicine, participants were instructed to wash their hands in water ranging from 40 degrees all the way up to 120 degrees. What the study found is that the temperature of the water doesn’t really matter when it comes to getting your hands truly clean.
The FDA recommends washing dishes at an uncomfortable 110 degrees as one of the steps to get rid of harmful bacteria. Interestingly, even though the FDA recommends washing your dishes at 110 degrees as one of its bacteria-killing steps, studies have shown that washing dishes in colder water can kill bacteria too. The difference may be in how quickly the grease comes off. Anecdotally, I can tell you that hot water makes for much easier scrubbing, as the remnants of a greasy meatball and spaghetti dinner just roll off the plate with hot water. Cold water can do the job too — it’ll just take more time.
Timing is everything
So what really does the job of getting rid of germs and bacteria when you’re washing your hands? Turns out time has a lot to do with it. A study at Northwestern University showed that people who washed their hands with soap for just five seconds did nothing to kill the germs on their hands. Conversely, people who washed their hands with soap for 30 seconds killed everything. As they teach my son in school — sing “Happy Birthday” two times while you’re scrubbing — that’s about how long it’ll take for your hand washing to really be effective. Also, don’t forget to scrub all the surfaces of your hands — in between your fingers, under your fingernails, and the backs of your hands too.
Remember, according to the Centers for Disease Control and Prevention, effective hand washing is the single most important defense against the spread of disease and infection. As a matter of fact, Oct. 15 is Global Handwashing Day — a day solely dedicated to raising awareness about the importance of washing your hands with soap.
Is there a difference between plain old soap and antibacterial soap? According to the Mayo Clinic, no. And antibacterial soap may even be detrimental to use, potentially causing bacteria to become resistant to the soap’s antimicrobial properties.
And of course, when you’re done, make sure to dry your hands on a clean, dry towel.
The bottom line? Though it’s true that warm water may be more comfortable for you to wash your hands with, it is not any more effective than cold water at getting rid of germs. And using cold water could save you a few cents too. Now that’s a nice, warm thought!
Editor's note: This story has been updated with new information since it was originally published in April 2012.