Fluorouracil may cause redness, soreness, scaling, and peeling of affected skin after 1 or 2 weeks of use. This effect may last for several weeks after you stop using the medicine and is to be expected.Sometimes a pink, smooth area is left when the skin treated with this medicine heals.luorouracil may cause redness, soreness, scaling, and peeling of affected skin after 1 or 2 weeks of use. This effect may last for several weeks after you stop using the medicine and is to be expected.