Scientists Actually Measured How Comfy Capybaras Feel When Bathing in Hot Springs

The furballs are suckers for a hot bath, for very good reasons.
capybara, japan, science, onsen, hot spring, research, bath, animals, rodent
Capybaras soaking in a Japanese hot spring filled with yuzu, a citrus fruit. Photo: The Yomiuri Shimbun via AP Images

Capybaras, the world’s largest rodent, understand that a nice long bath is one of the finer things in life.

Though native to South America, these chunky furballs are found lazing in hot springs in zoos all across Japan. With bliss written on these affable creatures’ faces, there’s no doubt capybaras enjoy the luxuries of a good soak.

But researchers in Japan just took bathing capybara a step further and proved, scientifically, that these cuddly creatures are actually quite relaxed when taking a dip—and how hot springs even improve their skin.

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Observing nine capybaras ranging from ages two to 12, zoology professor Tohru Kimura at Yamaguchi University and his student Kengo Inaka took notes during the creatures’ bathtime. The animals bathed for 30 minutes every day for three weeks, in water that measured 35 degrees Celsius, while the researchers measured how “comfortable” the rodents looked. 

“There are very few animals that actually look like they’re enjoying taking a bath,” Kimura told VICE World News, explaining why he specifically chose capybaras to research.

The semi-aquatic capybaras are often found living near bodies of water, which made it easier for the researchers to measure how the animals reacted to bathing in hot springs. Given that these fantastic swimmers originate from warm climates in South America, the animals take a dip in hot springs to stay warm in Japan’s winter months, Kimura added. 

To measure comfort, the capybaras’ facial expressions were key. After the researchers took hundreds of photos of the animals, both in the summer and winter, they developed a comfortability scale divided into three main categories: calm at baseline, moderately comfortable and obviously comfortable. 

capybara, japan, science, onsen, hot spring, research, bath, animals, rodent

The comfortability scale researchers developed. Photo: Courtesy of Tohru Kimura

The more wide-eyed and forward-facing their ears were, the less at ease the creatures felt. If their eyes were practically closed and their ears were pulled back, flaring out to the side, that meant the capybaras were obviously comfortable. 

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According to the study, there was a significant difference in how comfortable the capybaras looked before and during bathing, as noted by how open their eyes were. During a soak, the creatures’ eyelids would peacefully droop, almost as if they were sleeping. On the other hand, no significant difference was noted in the capybaras’ ears, though they did slightly flare outward mid-bath. 

The researchers also measured how much glossier and smoother the capybaras’ skin became after bathing consistently. 

In Japan’s dry winter, the capybaras’ normally soft summer skin hardened, turning crusty and scaly. Kimura also measured the moisture content of the animals’ skin using the German Corneometer instrument, which indicates the hydration level of the skin’s superficial layers, and found moisture content decreased in the winter. 

The researchers observed that 21 days of bathing gave the capybaras a glowy complexion, comparable to their summer skin, concluding that hot springs do indeed have dermatological benefits for the rodents. 

By scientifically proving that capybaras enjoy hot springs and come out with dewier skin, Kimura aims to demonstrate how beneficial these natural baths are for everyone—including humans. 

“Japan has many wonderful hot springs. There needs to be more scientific research on the health benefits of such baths, but I hope this encourages everyone to use onsen as a way to maintain good health, and to live long,” he said. 

Kimura plans to widen the scope of testing to humans, but conceded that fuzzy capybaras were a far more objective scientific subject. “They’re quiet animals and very friendly creatures. They can almost be like a friend,” he said. 

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