Fur chewing is thought to be both hereditary and environmental. The term is pretty self explanatory, it's when a chin literally chews on their fur.

If you have a chin in breeding who displays fur chewing, regardless if you think its hereditary or environmental, the animal should be removed from the breeding program.

Separate the animal and reduce the stress level as much as possible. If the animal is not alone, separate its cage mates as well to determine that the chin who has the chewed fur was the one actually chewing. Occasionally chewed fur is a result of cage mate. Either way, any chin displaying fur chewing signs should not be bred.