The female Spectacled Bears, Dolores, 15, Lolita, 11, and Bianca, 15, are losing hair from their heads, legs and parts of their backs.
Daily Bild reported late Tuesday that the animals appeared to be suffering a little-understood genetic defect that causes them to lose their fur when stressed.
"It's possibly the result of a power struggle. But there isn't a final diagnosis – and unfortunately no cure for it." An anonymous source told the paper.
The animals, which are native to South America and are also known as Andean bears, suffer from itchy skin, which is being treated with skin ointments.
“(The hair) hasn't completely gone, so the animals are scratching themselves. Germs seep in and the inflammation must with be treated with ointment,” the source said.
“Anyone with psoriasis or skin allergies can imagine how the bears are suffering. There is only treatment, no cure.”
Leipzig Zoo spokesperson Melanie Ginzel confirmed Bild's report.
“They have been suffering from this for a few years now and are in treatment. It goes through different phases of intensity,” she told The Local.
Despite the nasty autumn weather setting in, the bears are comfortable, Ginzel said.
“The bears are allowed to move where they please, and have a warm interior enclosure they can go to any time,” she said. “I saw one of them outside for a bit today but it's raining pretty hard and she went back inside directly.
According to Ginzel, an international symposium is researching the mysterious problem, but so far there have been no conclusions.
“We are not the only zoo to have this problem in the world," she said. "The bears are living with it.”