@lindasuzanne Welcome to Mayo Clinic Connect. Using florouracil seems to differ for many people. For me, my system reacts really well to it, meaning my skin gets very inflamed looking and irritated. My dermatologist has to remind me that means it is working ;)) I use a mild moisturizer after the first week, to minimize my discomfort. As for foundation, I use a powder, not liquid, most of the time, right over the moisturizer.

Here is what WebMD has to say about using this medication: https://www.webmd.com/drugs/2/drug-16269/fluorouracil-topical/details

As you will read many differing opinions, it is best to check with your own doctor, who knows your skin best.
Ginger