Even people who don't own pets may have pet dander in their homes. Pet dander is the tiny, sometimes microscopic skin shed by cats, dogs and other warm-blooded animals, such as rodents and birds. Pet dander can be carried into homes on people's clothing, which is how even homes and offices without pets likely have pet dander in them. Though dander is natural, it's also an allergy trigger for many people. But pet allergies are not entirely a result of pet dander, as the American Lung Association notes that allergens come from sources other than pets' skin. For example, the ALA notes that urine and feces from cats, dogs and other pets can cause allergic reactions in some people. Dust from dried feces can suspend in the air and eventually be inhaled by people with allergies, triggering a reaction. Pet allergens can maintain their strength for several months by sticking to clothing, walls and other surfaces. Pet owners with pet allergies can still keep their pets, but they must be prepared to make extra efforts to comfortably coexist with their pets. Removing wall-to-wall carpet, keeping pets off of furniture and keeping a home clean and free of clutter are some ways for pet owners to reduce the symptoms of their pet allergies. Wearing a mask while vacuuming also can reduce the severity of allergy attacks, as vacuums stir up dander and other allergens.