The Arctic is … cold, which is why polar bears (Ursus maritimus) need thick layers of fat and dense fur for insulation and, ultimately, survival. But for a few bears, staying warm this winter could be a challenge. According to research published online this month in the Journal of Wildlife Diseases, some polar bears are losing their fur—and the reason is unknown. Between 1998 and 2012, researchers temporarily captured nearly 1500 polar bears in the Alaskan region of the southern Beaufort Sea to collect information on their body condition and health status. They found that, over the study period, more than 3% of bears were losing fur along areas of their head and neck (such as on the bear pictured above). The number of bears with the syndrome—clinically known as alopecia—varied widely between years, with a maximum of 28% of bears displaying signs of fur loss in 2012. The recapture of several of the affected bears in later years suggests that the syndrome is not likely lethal and bears can successfully recover. However, individuals exhibiting fur loss were also thinner, indicating that the bears may also be stressed—either as a result of fur loss itself or from the other stressors contributing to the syndrome. Although the cause remains unknown, a number of factors—including environmental pollutants, nutrient deficiencies, infectious pathogens, or climate change—could be involved. Polar bears are listed as threatened under the U.S. Endangered Species Act, so scientists are concerned that any risk factor—including fur loss—could potentially threaten the survival of these iconic Arctic predators.