I have so far used level 1 and level 2 of the PH Optimum Retinol and have been amazed by the results. This is after using other retinol products in the past and having almost immediate bad skin reactions. Not so with these products. The redness in my skin disappeared within a couple of weeks. It works beautifully with Anti-Toxin Cleanse, Anti-oxidant vitamin serum and hydration serum. I say in all honesty, my skin has never looked better.