The instructions for Retin A include a warning to wait 20 minutes after washing to ensure face/neck are dry for "best results". I've seen some discussions on line that moisture will cause more irritation, but nothing about the actual "effectiveness" on wrinkles.
I can wait the 20 minutes but I live in a very humid place, plus I set the AC on 80 at the lowest, so I'm usually "moist" for a good while after face washing or a shower. Is this moisture causing reduced efficiency? I don't have irritation, and I'm using the full 0.1 now rather than the 0.05.