I've never gotten sick from the re-circulated air that I'm aware of; but one time, about 23 years ago (and I don't think they do this anymore); my family was flying to Mexico for a vacation....(this was before I discovered cruises) and right before we landed in Mexico the stewardess came through our plane and sprayed something in the air. When I asked her what it was, she said it was just an air freshner. Well, she lied to us. I have asthma and what I breathed wasn't an air freshner, it was something they were required to do back then (I think it's outlawed now) because we were landing in another country, to supposedly kill germs or something in the plane. What it did was make me extremley ill. We went to our room, I couldn't breath, we couldn't find a doctor in our hotel (which was a very expensive hotel) and we turned right around a came back home as soon as possible. We traveled 3000 miles to get there, and spent a lot of money on the trip and spent a lot of extra money to get back home and lost all of our money we paid ahead to our hotel in different cities in Mexico. We now go on cruises a lot and always buy insurance and we deal with a reputable cruise agent, which we didn't do back then. It was the worst travel experience I ever had, but we sure learned from it.