A friend whose kitten has been suffering severe asthma for months discovered that one of the triggers was the plastic flap on her kitty door; it smelled of petroleum. My cat suffers from asthma, but my kitty door has been up for 9 years, so I didn't think it could still be out-gassing. I was wrong. I smelled it and my glands immediately swelled up and didn't go down for over an hour. So this is just a heads up if you have anyone, 2 or 4 legged, with asthma or respiratory problems, check your plastic kitty flap. A neighbor has made a cotton one for my door which is working just fine.