How can I prevent my clothes dryer door from fogging up?
I went through this recently with my girlfriends dryer.   Here is what I learned:


Her outside vent hood seeped rainwater, not much but enough
Her ductwork had a tiny amount of lint which soaked up the rainwater
Her “outside air” ducting for the all-electric central heat and air system damper didn’t open all the way causing the air to be drawn from and through the dryer ducting.   The moisture in the ductwork lint was drawn into the clothing left in the dryer.   (Her house is new and sealed very tightly!)


An additional clue something wasn’t right was indicated by the exterior vent for her kitchen cook stove - it “rattled” when the air conditioner ran!

Solution:  


Replaced the dryer ductwork and exterior vent. 
Disassembled dryer and cleaned entire dryer ductwork path
Cleaned the central air exterior air feeder pipe, cleaned the exterior dampener
Replaced furnace filter.
Cleaned a/c condensate pipe (ran hose water through it until it was no longer 
draining “green” water)
Fixed her supper on the Weber charcoal grill.


She is happy now.  The dryer no longer “stinks” from the “wet lint” smell, her clothes remain dry and her air conditioner is working better.