Most people think an animal's hair causes allergies, but that's not altogether true. What they are really allergic to are the secretions of the sebaceous skin glands, the saliva, the dander (or dead skin flakes), and the urine residue, all of which contaminate the hair and all of which are major causes of allergic reactions. While pet hair itself is not a major cause of allergies, it serves as a carrier for those allergens that are. These allergens dry on the hair and subsequently flake off into the environment, along with dander, and become airborne as the animal moves about. They also enter the environment on the contaminated hair that pets shed, when pets are being stroked or groomed, when the shake, vigorously wag their tails, jump on furniture, play with toys and when they rub against objects. The longer a pet lives in a home, the more its allergens will have spread throughout the entire house.