A polar bear still hunting on the sea ice of Hudson Bay, Manitoba, Canada. (Credit:
© Jenny E. Ross)

DUBLIN — In the harsh Arctic environment, where polar bears regularly plunge into freezing waters to hunt seals, a remarkable thing happens: unlike your car windshield on a winter morning, their fur resists turning into a frozen mass. Scientists have long wondered how these marine mammals keep ice from forming on their iconic white fur, and now an international study reveals their remarkable secret lies in their greasy hair.

The study, published in Science Advances, dives into this furry phenomenon. An international research team, led by PhD candidate Julian Carolan from Trinity College Dublin’s School of Chemistry, has discovered that these white fluffballs possess natural ice-repellant reactions in their fur similar to advanced synthetic materials, thanks to a protective oil called sebum. This finding helps explain how polar bears stay ice-free while hunting in temperatures that can plummet below -40°C.

“We measured ice adhesion strength, which is a useful measure of how well ice sticks to fur; hydrophobicity, which dictates whether water can be shed before it freezes; and freezing delay time, which simply shows how long it takes for a drop of water to freeze at certain temperatures on a given surface,” explains Carolan, in a statement. “We then compared the performance of the polar bear hair with that of human hair and two types of specialist human-made ‘ski skins.’”

In Norway’s Svalbard archipelago, a cluster of Arctic islands roughly halfway between mainland Norway and the North Pole, researchers studied fur samples from six wild polar bears. The research team found that polar bear fur has remarkably low “ice adhesion strength.” That means ice simply doesn’t stick well to it. The key to this ice-resistant superpower lies in the bears’ sebum, produced by specialized glands near each hair root.

“The sebum quickly jumped out as being the key component giving this anti-icing effect as we discovered the adhesion strength was greatly impacted when the hair was washed,” says Carolan. “Unwashed, greasy hair made it much harder for ice to stick. In contrast, when the polar bear hair was washed and the grease largely removed, it performed similarly to human hair, to which ice sticks easily whether it is washed or greasy.”

The research team’s chemical analysis revealed something unexpected: Polar bear sebum lacks squalene, an oily compound commonly found in human hair and in other aquatic mammals like sea otters. Instead, it contains a unique mixture of cholesterol, diacylglycerols, and fatty acids that appear to have been specifically evolved to prevent ice buildup. This is especially important for polar bears when hunting.

“One of the polar bears’ main hunting strategies is ‘still hunting,’ where they lay motionless beside a breathing hole on sea ice waiting for seals to surface,” says professor Bodil Holst from the University of Bergen. “Still hunting frequently develops into an ‘aquatic stalk’ with the polar bear using its hind paws to slide into the water to pursue its prey, and the lower the ice adhesion, the less noise generated and the faster and quieter the slide.”

This natural technology hasn’t gone unnoticed by Arctic indigenous peoples. The Inuit developed sophisticated hunting techniques that mimicked polar bears’ advantages. They crafted hunting stools with polar bear fur-lined feet and wore “polar bear trousers” to ensure silent movement across the ice. Notably, traditional Inuit fur preparation methods specifically protected the sebum by never washing the hair-covered side of polar bear skin, unlike fox fur, which they would clean with soapstone or dry clay.

While other Arctic animals have developed different anti-icing strategies, polar bears’ solution is unique. For example, a penguin’s feather structure prevents icing rather than oils.

“Our work shows that polar bear fur provides an alternative strategy to produce an anti-icing surface based on the characteristic blend of lipids present in their fur sebum or hair grease,” says Dr. Richard Hobbs, Assistant Professor at Trinity College Dublin.

The discovery could lead to more environmentally friendly anti-icing technologies. Current synthetic solutions often rely on problematic “forever chemicals” like PFAS. The natural lipid coating produced by polar bears might offer a sustainable alternative for applications ranging from aircraft surfaces to winter sports equipment.