How polar bears stop ice from freezing on their fur

Polar bears have a hidden-in-a-plain-sight superpower that anyone who has watched a wildlife documentary could have spotted: ice doesn’t stick to their fur.

This has long been known to Indigenous peoples of the Arctic, who have utilised this property of the fur, but only now has it been noticed and studied by scientists. Bodil Holst at the University of Bergen in Norway and her colleagues have shown that the ice resistance of polar bear fur is due to natural oils secreted onto the hairs, rather than a property of the fur itself.

Holst is a physicist who studies the properties of surfaces. Her interest in polar bear fur began when, while watching a TV quiz programme, she saw that the bears barely show up on infrared cameras because they are so well insulated. That means the temperature of their outer fur is below freezing, Holst realised, but she had never seen a polar bear in wildlife films that was coated with ice, even after swimming in sub-zero waters.

“And then I thought, well, how come freezing is not a problem? How come you don’t get accumulation of ice on the fur under these circumstances?” she says.

This is, after all, a problem for many other land mammals in cold environments, from musk ox to bearded polar explorers. Holst asked researchers at Norway’s Polar Research Institute if they knew why polar bear fur doesn’t ice up. None did, but they decided to investigate together.

Holst and her colleagues obtained samples of polar bear fur from Svalbard in Norway and compared them with human hair. They found that the force required to remove ice from polar bear hair was a quarter of what was needed for human hair – meaning the bears can easily shake any ice off.

Washing polar bear fur removed its ice resistance, suggesting that the oily coating on the hairs is the key to its properties. This substance, known as sebum, is secreted by glands connected to hair follicles.

Polar bear sebum lacks a substance called squalene that is commonly found in sebum, especially in aquatic mammals, the team found. It also contains some unusual fatty acids. These could be unique to polar bears, but we can’t be sure of that, as so few studies have looked at the composition of animal sebum, says Holst.

Arctic peoples such as the Inuit have traditionally prepared polar bear fur in a way that preserves the sebum, unlike methods used for other furs. They have also used the fur in ways that make use of its ice-resistant properties.

For instance, Inuit hunters in Greenland are known to have placed small pieces of polar bear fur under the legs of the stools used by hunters, to stop them sticking to ice. They also strapped polar bear fur to the soles of boots while stalking animals, to avoid the noise made by ice-coated surfaces.

Holst’s team is now exploring potential applications, such as creating environmentally friendly ski waxes that don’t contain the long-lasting fluorocarbon compounds currently used to prevent icing.

A hair wax based on polar bear sebum could also help people who work in cold environments. “I had not thought about that application, but absolutely, that should work,” says Holst. “I think you’ve just given me a new idea.”