Fluorouracil (5-FU) topical treatment is a chemotherapy agent primarily used in dermatology to address specific skin conditions like actinic keratoses (sun-damaged precancerous lesions) and superficial basal cell carcinomas. This medication works by targeting and destroying rapidly growing, abnormal cells in the skin while having minimal impact on healthy surrounding tissue. The therapeutic process involves a predictable and visible reaction on the treated skin, which indicates the medication is actively working to eliminate damaged cells.
Early Skin Changes
Within the first few days to a week of fluorouracil treatment, the skin typically starts to show its initial reactions. The most common early visible sign is increasing redness, medically known as erythema, in the treated areas. This redness may appear blotchy and is often accompanied by a feeling of mild irritation, burning, or stinging. The skin may also feel dry and tender, with some individuals experiencing a sensation of tightness. This initial inflammatory response signals that the fluorouracil is beginning to work on the sun-damaged or cancerous cells.
Peak Reaction and Skin Breakdown
The reaction to fluorouracil intensifies, reaching its peak around the second or third week of treatment. During this period, the skin will show significant inflammation, appearing intensely red and swollen. Blistering commonly develops, followed by crusts and scabs as damaged skin cells are shed. Erosion of the skin surface may occur, leading to raw areas that can sometimes ooze fluid. This intense and sometimes unsightly appearance is an expected part of the treatment process, indicating the medication is effectively destroying the targeted abnormal cells.
The Healing Process
Once treatment is completed or the peak reaction subsides, the skin begins its recovery, leading to noticeable visual changes. The crusts and scabs formed during the intense reaction will gradually fall off. As these layers detach, new skin is revealed underneath, typically pink or reddish in color. The inflammation will progressively diminish, and the skin will become smoother as re-epithelialization occurs, where new skin cells grow and cover the treated area. During this healing phase, discomfort, itching, and tenderness typically decrease as the skin regenerates.
Long-Term Skin Appearance
Weeks to months after treatment completion, the skin generally returns to a more normalized appearance. Treated areas often appear smoother and healthier due to the removal of damaged cells. While the skin typically recovers well, some subtle long-term changes may be observed, such as slight hypopigmentation (lighter areas) or hyperpigmentation (darker areas). These pigmentation changes usually fade over time. A very mild, fine texture change in the skin is also possible, though significant scarring is uncommon with topical fluorouracil treatment, especially when applied as directed.