Washing Hands in Hot Water Wastes Energy, Study Says

I always thought the purpose of hot water was to improve the reaction between the soap and the oils on your hands.

Use cold water, and the oil thickens, which makes it harder to emulsify, and less likely to get washed away in the water. Use hot water, and the oils are easier to wash away. Oils can trap dirt and bacteria, so washing them away makes your hands cleaner.

There's a telling quote from the article that makes me think they're not really studying what they should: " Even water as cold as 40°F (4.4°C) appeared to reduce bacteria as well as hotter water, if hands were scrubbed, rinsed, and dried properly."

But how do they fare when hands aren't scrubbed rinsed and dried properly, and does the average person scrub, rinse, and dry their hands properly? More importantly, are they more likely to do so if the water is pleasantly warm? If hot water helps in the actual common case, then it's still important.

Interesting from a biology/chemistry perspective, but also perhaps a really good example of missing secondary effects.

"The agencies do recommend using soap and water and scrubbing vigorously, for at least 20 seconds."

I spend a whole lot more time scrubbing when the water is nice and warm.

""You don't need hot water, you need soap, water, and friction," said Sack. He added that the Escambia County Health Department in Pensacola, Florida, decided to turn off the hot water heaters in its five clinics two years ago, after a review of the literature provided no evidence that hot water was better."

... and did turning off the hot water have impact on compliance with hand washing policy? That would be an interesting follow-up study.

The researcher interviewed in this article, Amanda Carrico, has three degrees in psychology.[1] I'm not sure why I should trust her to do a review of the microbiology literature.

[1] http://www.vanderbilt.edu/viee/profiles/amanda-carrico.php

"if hands were scrubbed, rinsed, and dried properly."

... which never happens. Seems like the same faulty logic used to justify blow-driers over paper towels.

It doesn't look like the study that would actually answer this question (randomly assigning bathrooms heated and unheated water, doing hand swabs on leaving patrons) has actually been done, but if I were in a position to gamble on the outcome, I'd bet the cold water bathroom gets substantially less effective cleaning for human-factors reasons.

Maybe. But my hands feel better with hot water.

This whole time I've been taking hot showers for nothing.

IF you use cold water, your body has to make up the lost heat. This requires energy which comes from burning calories, meaning you will have to eat sooner. Food is not free energy, and in many cases is probably a lot less efficient energy-wise than hot water when you think about the energy it takes to grow, prepare, package, and ship it.

This is why I started the Lukewarm Water Hand Washing Awareness Coalition (LWHWAC). We've been fighting for years to raise awareness of the dangers of washing hands in both hot and cold water by lobbying to get our messages in schools, holding bake sales, running TV and radio advertisements, streaking through hot water heater sections of department stores, and holding flyering campaigns.

In other news: The sky is blue.

Well, it's actually grey right now. Sigh.

So the surgeon should use cold water before gloving?

It seems more sensible to heat the water at the tap like they do in Germany and Barbados.

Shouldn't the use of good antibacterial soap remove most [99%, as advertised] of the bacteria anyway?

I knew it!