Topical fluorouracil therapy is a major advance in the treatment of actinic keratoses. With extensive use, some untoward results can be anticipated. Contact dermatitis, both to the agent itself and to the vehicle in which it is employed, may occur. Acquired sensitivity occurred in a little more than 1% of the patients treated. Preexisting dermatoses may be accentuated by the inflammatory response which ensues from this procedure. Patients with chloasma and rosacea are most likely to encounter temporary accentuation of the underlying disorder. Pretreatment instructions regarding the expected reaction and weekly observation is recommended. Exposure to sunlight increases discomfort at the reactive stage but is not an absolute contraindication to treatment.
Sams WM. Untoward Response With Topical Fluorouracil. Arch Dermatol. 1968;97(1):14-22. doi:10.1001/archderm.1968.01610070020003