Shelf life of opened tretinoin

Question: I have been using the obagi Nuderm system for 3 or 4 years now and the results are just amazing, love it! The only problem though is that each time I start a new tube of tretinoin (.1%), I go again through a peeling/redness phase for a month or so. I guess that means that after a while, tretinoin loses activity in an opened tube, and my skin has to adjust again when I start a new one. Does that make sense? Is this something that has been reported by Obagi users? Since I don't have severe skin damage, I am thinking of switching to .05% that might be more gentle. Thanks in advance for your response/advice.

Once a product has been opened the stability and/or effects of it can become compromised. Do consider changing the concentration you use now. And also consider using a non-prescription retinol. Best skin care wishes.

Meagan, Esthetician