Cats and dogs
About half of U.S. households have a cat or a dog, and an estimated 10 percent of the population may be allergic to these animals. Allergens from cats and dogs are found in skin cells the animals shed — which is known as dander — and in saliva and on hairs.
Dander is particularly problematic because it's small and can remain airborne for long periods of time, and because it easily accumulates on clothing, curtains and upholstered furniture. Pet saliva can collect in carpets, bedding, furniture and clothing, and dried saliva can also become airborne.
Like other allergies, reactions to cats and dogs can range from mild to severe. Some people receive allergy shots to cope with exposure, and some can simply take over-the-counter antihistamines to relieve symptoms. So-called hypoallergenic cats and dogs may shed less than other pets; however, no breeds are truly hypoallergenic.