This is something I haven't seen before. Only my drivers side mirror (which is the only one that has the defrost option) fogs up if I don't keep the defrost on. The passengers side mirror has no issues with fogging up. Has anyone experienced this before? I tried searching the forums but didn't see anything like this.

2000 Chevy Blazer 4-Door

 

i havent experienced that, its a little weird. is it all the time or just at certain temps/weather conditions?

also if it continues rain-x makes a anti fog wipe you could use, it has worked so far for my windshield

 

I will try that. It is the strangest thing.

 

Check the glove box options list to see if DDO is listed. If so, then the mirror is the auto dimming type and what has happened is the fluid inside the mirror is leaking-out. The fogging will only get worse.
I just had this happen to my '02. Never could find an exact replacement so had to go to a non-auto dimming mirror. There are cheap mirrors on ebay and what I think is a better one by K Source. Check out RockAuto for the K Source and ebay for the cheap ones.