Children are particularly at risk, especially when you consider that some five million children in the U.S. suffer from asthma. There are several causes of indoor air pollution. Many of them sound disgusting, but we need to discuss them anyway. Animal dander and hair are a big pollution source. Many people have allergic reactions to dander and hair.
Cats are a particular problem because they lick themselves.
So, the hair also contains saliva, and both can trigger reactions. If this poses a problem, it might be best to keep your pets outdoors, if possible. At a minimum, keep them out of your bedroom and carpeted indoor areas. Feathers are also problem. They can trigger allergic reactions even if they are contained within pillows or mattresses.