Cats actually have more allergens on them than do dogs. Dogs just have the fur, which tends to be kinda wiry and doesn't shed too much in most breeds. Cats' fur is much finer and sheds constantly, except for the Norwegian Forest Cat, which is a naturally occuring hypoallergenic breed that doesn't shed. Anyway, cats lick their fur. Their saliva dries into a fine film, cracks up, and atomizes into the air. It is, for all intents and purposes, almost identical in shape and size to pollen. With more allergens come more allergies.