A patient with actinic keratoses was treated with three different fluorouracil preparations topically without the development of reaction. Purposeful exposure to hot sunlight failed to cause any inflammation even though he was applying the fluorouracil at this time.
Epstein E. Resistance to Fluorouracil. Arch Dermatol. 1969;100(5):587. doi:10.1001/archderm.1969.01610290071014