Animal dander is loose skin cells (like dandruff) from animals such as dogs and cats. These skin cells, which contain secretions from glands in the animal's skin, float in the air, where they may be breathed in by people.
Animal dander is an allergen. Animal fur or hair is not an allergen. When a person is allergic to an animal, such as a dog or cat, the allergy may be to animal dander (skin cells) or to dried saliva from the hair of a cat.