This happened to my ferret back in 1987 and I was told by my vet that it is a dietary problem where there aren't enough lipids in the diet. The skin dries out and hair loss begins. I was given a supplement to put into the food and within a few weeks the hair had grown back. I assume this is correct because it worked. Using foods designed for ferrets this has never happened to me again. -Clint [Posted in FML issue 3819]