I don't know what it is about the hair. Some allergists claim it's the saliva on the fur, the animal's feces and urine, or their skin dander, texture of the fur, etc. It doesn't matter. All I know is that I am allergic to labs, boston terriers, shepards, collies, and a lot of other dogs (and all cats)...I am NOT allergic to bishons, cairns, yorkies, poodles, and many other little yappers. The boston terrier's fur may be thin like an eyelash, but for some reason, it makes me itch and sneeze. Because I can't help myself, I pet her cute little body and then immediately have to go wash my hands. Hives central if I don't. I don't get it...I don't even bother trying to figure out why I am allergic to some and not all. It took us a LONG time to find an animal that could become a housepet when difficult child was little and we discovered cairns. They are the perfect mix of rough and tumble in a small package, lol.