Are essential oils dangerous for rabbits to inhale or use on their fur?

A week ago I read a book regarding different use for essential oils. One of the chapters talked about rubbing eucalyptus oil and some other oils in the fur could help with their respiratory issues. Personally it sound like a stupid idea since rabbits is always licking themselves. Would use of a vaporizer with pure eucalyptus essential oil be okay? All my rabbits have flare-ups in the cold months, so any little extra things I can do to help them would be nice.