Wow ... I picked this up at a spa in New Orleans just before the flood. This was recommended to decrease pore size and even skin tone. The aesthetician gave me Level 9 and didn't say anything about building up. I had never used retinoids so she warned me to start sparingly. It did take a couple of weeks for my skin to adjust ... but wow. I don't use it every day but when I do ... it's a huge improvement. Just wish I could control the pump better because one press is too much.
edited to add: I've been an Avene convert for years now.