Do you wash your hands in hot water? You’re not alone. Most people think that higher temperatures improve hygiene. It’s not true, though, and the misinformation has significant impact on global warming.
Everywhere you go, from home to school to work to public restrooms to hospitals, you are reminded to wash your hands. And with good reason: the US Center for Disease Control (CDC) confirms that handwashing is the single most effective way to prevent the spread of disease. Concentrated efforts at educating the public on this important, individual contribution to public safety has led to those signs you see in restrooms, as required by law.
Normalization of handwashing practices has been largely successful nationwide. Unfortunately, misconceptions about proper cleaning methods are prevalent and dangerous.
By now, most people know that washing your hands is the healthy thing to do. The practice has become commonplace; 92% of US Americans agree that handwashing is important. Most people even understand that too much soap is harmful to the environment and are conservative rather than wasteful. What most people don’t realize, though, is that warm water is not necessary for proper hygiene. Even governmental levels of public advisory recommend using warm or even hot water – without any scientific basis for the recommendation. “Wash hands using warm water” sounds more effective than it actually is, and the consequences are serious for the environment.
The purpose of washing our hands is to remove organic matter that can harbor bacteria and viruses so that disease is not spread. If you could remove all traces of food or grime from your hands with plain water, you wouldn’t need soap at all. Soap or detergent is generally necessary to cut through oils, though, so they can be lifted from the skin’s surface and washed down the drain.
Research mainly focused on every aspect of handwashing except water temperature.
The concept of handwashing as a method of disease prevention was first introduced by the Hungarian physician Ignaz Semmelweis and taught by the English founder of modern nursing, Florence Nightingale, in the mid-1800s. Since then, there has been extensive research on the best methods of cleaning human hands to prevent cross-contamination and the spread of disease. Tests and comparisons are performed on aspects such as the type of cleaning agent used, duration of the cleaning process, and cleaning steps like using a nail brush or antibacterial rinse. Almost none of these studies refer to water temperature. The lack of definitive research on this variable allowed untested traditional practices to continue.
According to a broad study at the Vanderbilt Institute for Energy and Environment, 64% of us use hot water to wash our hands, and almost 70% believe that warmer water increases the effectiveness of handwashing. The belief that warm water helps in cleaning probably traces back to the use of lye soaps made before the introduction of detergents at the start of the 19th century.
Carbon emissions produced by heating water for handwashing in the USA is the equivalent of 1.25 million cars each year.
Using hot water for handwashing seems like an insignificant detail. The next time you wash your hands, though, think about this: US Americans wash their hands about 800 billion times each year, and 64% of them use hot water. Heating water for that requires energy. In fact, carbon emissions produced by heating water for 800 billion hand scrubs each year equal 6 million metric tons of CO2 equivalent emissions. That is equivalent to the emissions of about 1.25 million cars each year – around 0.1% of total emissions or 0.3% of residential and commercial sectors each year.
A common belief is that warmer water is better at killing pathogens. While it is true that boiling water can kill waterborne germs, it is too hot for washing skin. What we consider “hot” water is somewhere between 105° and 130° Fahrenheit. Water temperature above 120°F may kill some pathogens if the temperature is maintained for some time, but would quickly burn human skin. Even at the lower range, hot water can damage the skin, causing it to be more susceptible to infection. Hot water is also uncomfortable and requiring its use has the opposite effect: people skip washing their hands rather than washing them in painfully hot water.
Today, we know that water temperature is irrelevant to the efficacy of handwashing. Handwashing is effective if the skin and nails are scrubbed, rinsed, and dried properly. Choosing a comfortable water temperature lowers the impact to global warming. It’s also more likely that people will actually wash their hands correctly, creating a healthier environment for humans, too.
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