Cold and cold
 

Recently, after a flight I developed a cold and sore throat. Onee of my friends remarked that I often catch cold after a flight, particularly during winter.
Here is my theory: In winter when it is cold, pilots recirculate more inside air and bring-in less fresh air. In other words, more germs are recirculated.
My questions:
a) Does outside temperature dictate (guided by economics) how much fresh air is mixed in the cabin?
b) I assume that some kind of filters are used when air is recirculated. Are they capable of filtering cold viruses?
c) How often these filters are changed?

I don't know the answers to any of your questions, but I do know this: winter is the cold and flu season, where more people spend more time indoors, spreading germs around to each other, and even if the recirc on a plane is exactly the same in winter as it is in summer, the liklihood is that there are more germs coming aboard with the pax in winter than in summer.

The outside air at cruise altitude is always extremely cold regardless of the season, so the amount recirculated won't change significantly (if at all). As WillCAD notes, it's simply a matter of being surrounded by more sick people.

(Media myths about recirculated air on airlines is one of Patrick Smith's favorite pet peeves - here's one of his interesting articles on the subject.)

Also, I think it's pretty rare to catch colds from viruses that are floating through the air - much more likely that you've touched a tray table, IFE touchscreen, seat back, or other item that's been in contact with a sick person.

Nevermind - rjw242 answered my question.

One year I had four colds in a row, it was like clockwork, Nov, Dec, Jan, Feb.. All starting right after flying home.

I started washing my hands like someone with OCD and haven't had one since, that was over 2 years ago.

Air is constantly drawn in from outside to keep the cabin pressurized. The AC packs keep the temperature comfortable, they mix outside air with engine bleed air and introduce it to the cabin. I am not sure about recirculating, not that familiar with the subject, need to dig up the maintenance manuals.

And I never get colds. I've had exactly one in the last 20 years :P

Lucky you! I don't so much mind it at home, but it's kind of a drag away from home. Congested ears on a plane make me want to murder them. :td:

Ditto.

Okay, I admit, I did get a bad sinus infection in 1996 (Christmas Day, went to the ER for antibiotics), so yes, I have gotten sick in the last 20 years.
:)

Winter if cold season.. Gotta have good hygiene.

Some scientists will point to evidence that doesn't agree with you. :o

Wow. I wish my body is as anti-cold as yours.

That's not to say I don't get sick; if there's a stomach virus flying around, it finds me even with scrupulous hygiene. I just don't get colds.

And I'd rather get the stomach stuff than colds because my husband always gets colds and those things last forever. Yeesh.