Cedar as bedding...

The only bedding I ever use is cedar shavings - just in the nestboxes and broody boxes, now. We're in a hot, humid climate so my first goal is to keep bugs away. And also because of the hot climate, I keep them as ventilated as possible. I also raised my first chicks on cedar - again, with a great deal of ventilation.

My feeling is, if they're kept so hot and enclosed that fumes from the bedding hurt them, they're way too hot and enclosed.

My hens are 19 months now, in good health, laying. There have been no mysterious deaths, and the eggs have a high fertility rate.

 

If you have the choice.... cedar vs. pine or hardwood.... I'd avoid the cedar. You may not have problems with it, like above poster says, but then again you might.....

 

it is aromatic cedar that causes issues. An easy test would be to chip up some of your cedar put it in a box and stick your head in the box for an hour. Nap time!
If it irritates your nose or lungs, your cedar should not be used for chickens.
As was stated before if you have enough ventilation you should be fine.