A dozen pandas at the Chengdu Research Base of Giant Panda Breeding appear to be losing their distinctive black eye patches. Their plight got attention on social media after users posted pictures of pandas whose eye patches appeared to be turning white, Quartz reports.

What's actually happening: The pandas are losing fur around the eyes. A team of experts has been attempting since January to figure out the root of the problem, but so far they're stumped, China Daily reports.

A report from the team says the pandas are suffering from "partial depilation around the eyes," but lists no cause, the Global Times reports. The team has ruled out uveoencephalitis, a disease that can cause hair loss; it's possible bacteria or mites—both of which can thrive in the humid climate of Sichuan province—are causing the issue, and indeed, some pandas at the base have reportedly been infected with mites.

But treatment for mites proved ineffective. The affected pandas are quarantined and another medicine will be attempted, and the base says it is cooperating with Sichuan Agricultural University to come up with a solution.

(Here's why pandas are black and white.)

This article originally appeared on Newser: In China, Some Pandas Are Losing Their Black Eye Patches