This is really interesting for those that are worried about the cat or dog that is in sight. There was much more if any of you all would like to read, I will add the link
Pet dander is present in nearly all homes in the United States -- including those without any animals. This was the key finding of a research study published in the July 2004 Journal of Allergy and Clinical Immunology. Dogs and cats lived in only half of the residences examined in the study, conducted by the National Institute of Environment Health Sciences Institute. Results suggest that people who are sensitive to cat and/or dog allergens are highly likely to be exposed to detectable levels of those allergens in their environment regardless of where they live.
The researchers used data from the National Survey of Lead and Allergens in Housing, in which surveyors collected vacuumed dust samples from beds, bedroom and living room floors and living room sofas in 831 housing units in 75 randomly selected locations around the United States.
Dog and cat allergens were detected in 100 percent and 99.9 percent of homes, respectively, even though only 49.1 percent of the homes actually had such a pet.
Interestingly, the researchers found that dog and cat allergen levels were higher among households belonging to demographic groups in which dog or cat ownership was more prevalent, regardless of whether or not the household had a pet. Because dog and cat allergens can be transported on clothing and shoes, the researchers speculated that the community, particularly where dog or cat ownership is high, may be a primary source of these pet allergens. For pet-allergic patients in such communities, allergen avoidance may be difficult.
The vacuum samples revealed that sofas had the highest concentrations of allergens, even in homes without pets, again suggesting that residents and/or visitors brought the allergen material in on their clothing.
Researchers noted that cat dander is a very hardy antigen that stays in the environment for years after a cat is gone. People with severe allergies can reduce their risk by using high-efficiency filters and avoiding plush furniture and carpet.
Other research has shown dog and cat allergens to be prevalent in places like bus seats, park benches, theater seats and waiting rooms in hospitals and allergists' offices. Therefore, "it may be that people who are very allergic to dogs and cats may have to rely on medications as opposed to avoiding exposure," said scientist Samuel Arbes, who worked with Darryl Zeldin on the study.
http://www.paw-rescue.org/PAW/PETTIP..._Allergies.php