People typically wash their hands seven times a day in the United States, but they do it at a far higher temperature than is necessary to kill germs, a new study says. The energy waste is equivalent to the fuel use of a small country.

Amanda R. Carrico, a research assistant professor at the Vanderbilt Institute for Energy and Environment in Tennessee, told National Geographic that hand washing is often “a case where people act in ways that they think are in their best interest, but they in fact have inaccurate beliefs or outdated perceptions.”

Carrico said, “It’s certainly true that heat kills bacteria, but if you were going to use hot water to kill them it would have to be a way too hot for you to tolerate.”

Carrico said that after a review of the scientific literature, her team found “no evidence that using hot water that a person could stand would have any benefit in killing bacteria.” Even water as cold as 40°F (4.4°C) appeared to reduce bacteria as well as hotter water, if hands were scrubbed, rinsed(冲洗)and dried properly.

Using hot water to wash hands is therefore unnecessary, as well as wasteful, Carrico said, particularly when it comes to the environment. According to her research, people use warm or hot water 64 percent of the time when they wash their hands. Using that number, Carrico’s team calculated a significant impact on the planet.

“Although the choice of water temperature during a single hand wash may appear unimportant, when multiplied by the nearly 800 billion hand washes performed by Americans each year, this practice results in more than 6 million metric tons of CO2 equivalent emissions annually,” she said.

The researchers published their results in the July 2013 issue of International Journal of Consumer Studies. They recommended washing with water that is at a “comfortable” temperature, which they noted may be warmer in cold months and cooler in hot ones.

Some dogs are exceptional. Take Chaser for example, an American border collie (边境牧羊犬) regarded as the “smartest dog in the world”, who could recognize and remember 1, 022 nouns — one for each of her toys. In Germany, another border collie, a male named Rico, practiced “fast-mapping”, or figuring out the names of new things with the speed and cleverness of a three-year-old child.

Yet such examples of dog genius are often “about only one dog”, says Claudia Fugazza, an ethologist who studies dog cognition (认知) at Budapest’s Eotvos Lorand University. She and her colleagues asked owners of 34 pet dogs of various breeds (品种) to teach their dogs names for two separate toys. Out of those 34 animals, only one dog passed the test — a border collie named Oliva. “These results mean talent must be something special,” says Fugazza, lead author of a new study on the experiment.

The scientists looked for dog owners worldwide via social media, then asked them to play fetch with their dogs daily in their homes while repeating the name of the toy, a process that lasted three months. Once a month, with a scientist present, the owners tested the dogs—the study participants included both adults and little dogs — by asking the dogs to fetch one of two toys by name. Dogs that succeeded were then given a new toy and new name to learn. Despite the intensive training, only Oliva learned to match a single word to a toy — in fact, she learned 21 names in two months.

“None of the breeds learned a thing. It was such a surprise,” Fugazza says. To check if the study design worked, the scientists also tested six border collies that could already fetch some toys by name; as predicted, all six of those control dogs, including a dog named Nina, learned additional names.

It’s interesting that 18 of the 33 dogs that failed the test were also border collies, Fugazza points out, showing that the breed isn’t always high performing.

Because of such individual difference, the scientists next plan to track the genetics(基因) and history of a variety of dog breeds to try to identify the factors that produce such smart creatures.