Update 10/20/19 – I no longer use Paula’s Choice C15 super booster. I don’t know if they changed their ingredients or if something changed with my skin but it irritates my skin and makes it red/blotchy. I also feel a burning sensation immediately after applying it to my skin. This all began about two months ago and prior to that, I had no problems. So YMMV.
I bought the C15 serum because my favorite Vitamin C serum was discontinued. I have a like/hate relationship with Paul’s Choice** and would prefer to use any other brand…except well, Skinceuticals is just too expensive and their patent doesn’t expire until 2025.