I saw part of one this morning, examining the germs in people's cars. For one, they put a petri dish in front of the a/c vents, turned them on for a bit, then grew the petri dishes. They found some form of
Penicillium from this. The woman was greatly concerned now, because she has a three-year old, and she tries to keep everything so clean for him because he's a child and his immune system isn't fully developed. Note that it wasn't the poor immune system of some sort of illness, just the general I'm a child and haven't been exposed to as many pathogens as an adult kind that every child has. Anyway, she was very worried about his breathing
Penicillium, so she had the a/c filter replaced (which will help for a little bit) and then sprayed an antibacterial spray into the vents. I had to turn it off after this, I was afraid I might get as clueless as her if I watched much more. If you don't see where the problems in this story are, I encourage you to be proactive in learning more and do some searches, particularly for a little more information about
Penicillium. That should explain it for you.