My last car was a Buick Century. Near the end of it's life, if I ran the heater for a while I would get a minor headache. Well, it was old and nearly at the end of it's life, so I figured I would let it go until I bought a new car. Within 6 months the power steering broke and I bought my new car - a 2009 Toyota Prius with 15,000 miles on it. I live in Minnesota. Unfortunately, I've found that my Prius is even worse in this regard. It's like this - 1. Roll down the windows to air out the car then roll them up again (for all of the following) 2. Heater off, fan off - no problem, have driven a long time with no issues. 3. Heater on, recirculating air inside car - slightly headache after a while 4. Heater on, outside air coming in (usually on the thing that blows air on the windshield and keeps the windows from steaming up) - noticeable headache. Sometimes I notice within a few seconds, sometimes it takes a few minutes. I was wondering if anyone had had the same problem and knew of any solutions. I've paid the dealership to check for exhaust leaks and they said there weren't any. I don't know what the person before me had, but I haven't had any air fresheners or carpet cleanet chemicals or anything in it since I bought it (almost a year ago). I also had them replace the cabin air filter. I've read about there being a mold problem in Prius's where people run the air conditioner all the time, but I don't do that - I live in Minnesota so I've hardly run the air conditioner at all. I'm not sure where the car is from, but I leave the car parked outside all winter - I would think any mold would have been cleared out by the subzero freezing temps in the winter. And while the car has a slightly "locker room" smell to it, it doesn't get any better or worse when I turn on the AC. And it's a 2009 model which supposedly has the new evaporator coil and such that Toyota thought would fix the problem. This last weekend I rode in a relatives Mitsubishi Outlander for 3 hours and was reminded that not all cars give me a headache when I ride in them (though to be fair, we were running the AC not the heater. Has anyone else had this problem? Has anyone heard of a solution?