Fluorouracil cream is a topical chemotherapy medication used primarily to treat actinic keratoses (rough, scaly patches caused by sun damage) and certain superficial skin cancers. It works by stopping abnormal skin cells from multiplying, causing them to die and eventually peel away. The cream is applied directly to affected areas, making it one of the most effective at-home treatments for precancerous skin lesions.
Actinic Keratosis: The Most Common Use
Actinic keratoses are the number one reason doctors prescribe fluorouracil cream. These rough, sandpaper-like patches develop on sun-exposed skin, particularly the face, scalp, ears, forearms, and backs of the hands. Left untreated, a small percentage of them can progress to squamous cell carcinoma, a type of skin cancer. Fluorouracil cream treats not just the visible spots but also the surrounding “field” of sun-damaged skin, catching lesions too early to see with the naked eye.
The results are strong. In a large comparative trial, 75% of patients treated with fluorouracil cream achieved at least a 75% reduction in their actinic keratosis lesions at 12 months. That outperformed every other topical option tested: imiquimod cleared lesions at that level in 54% of patients, while photodynamic therapy reached 38% and ingenol mebutate just 29%. The National Institute for Health and Care Research highlighted fluorouracil cream as the best first-line treatment based on these findings. The American Academy of Dermatology also gives it a strong recommendation in its clinical guidelines for actinic keratosis.
Superficial Basal Cell Carcinoma
Fluorouracil cream is also used to treat superficial basal cell carcinoma, the most common and least aggressive form of skin cancer. “Superficial” means the cancer is confined to the top layer of skin and hasn’t grown deeper. In these cases, the cream can eliminate cancerous cells without surgery. It’s sometimes used as an add-on treatment after surgical removal to target any residual superficial cancer cells at the wound site, with recurrence rates as low as 3.7% in follow-up studies.
Fluorouracil cream is not appropriate for deeper or more aggressive skin cancers. Your dermatologist will determine whether a lesion qualifies for topical treatment based on biopsy results and the tumor’s depth.
Off-Label Use for Warts
Some dermatologists prescribe fluorouracil cream off-label for stubborn warts, particularly plantar warts on the soles of the feet that haven’t responded to other treatments. In a crossover study of patients whose plantar warts didn’t clear with tape occlusion alone, adding fluorouracil cream under occlusive tape twice daily achieved a 100% cure rate among enrolled patients, with an average time to cure of about 8 weeks. Patients reported little to no pain and only mild skin irritation. This approach is typically reserved for warts that have resisted standard treatments like freezing or salicylic acid.
How the Cream Works
Fluorouracil belongs to a class of drugs called antimetabolites. Once absorbed into rapidly dividing skin cells, it interferes with DNA production. Specifically, it blocks an enzyme those cells need to build new DNA strands. Without the ability to copy their genetic material, the abnormal cells can’t reproduce and begin to die. The drug also gets incorporated directly into the DNA of these cells, creating defects that trigger a self-destruct process.
Normal, healthy skin cells divide much more slowly than precancerous or cancerous ones, so they’re less affected. This selectivity is why treated areas “light up” with inflammation exactly where the damage is, revealing hidden lesions you may not have known were there.
What to Expect During Treatment
A typical course of fluorouracil cream for actinic keratosis lasts two to four weeks, applied once or twice daily depending on the concentration prescribed. The cream is available in several strengths, with the 5% formulation being the most commonly used for actinic keratoses.
The treatment follows a predictable pattern that can look alarming if you’re not prepared for it. During the first week, you may notice mild redness and tingling at the application sites. By weeks one to two, the skin typically becomes noticeably red, irritated, and may start to peel or crust. This is the medication working: it’s selectively destroying damaged cells. The reaction often intensifies through the end of the treatment course, and the treated skin can look raw, swollen, or even scabbed over. This inflammation can persist for several weeks after you stop applying the cream.
Once the damaged cells have been destroyed and you stop treatment, healing generally takes two to four additional weeks. New, healthy skin grows in to replace the destroyed tissue. Many people find their skin looks and feels smoother after healing than it did before treatment.
How to Apply It Safely
Wash your hands thoroughly before and after every application. Apply a thin layer only to the affected area, and avoid getting the cream on healthy skin, in your eyes, or on mucous membranes. If you use your fingers to apply it, wash them immediately afterward. Any applicators or tools used should be cleaned or discarded.
Sun protection during treatment is essential. The treated skin is more sensitive to ultraviolet light, which can worsen irritation and increase the risk of burns. Wear broad-spectrum sunscreen, protective clothing, and a wide-brimmed hat when outdoors. This applies throughout the treatment period and for several weeks after you finish, since the skin remains vulnerable while healing.
DPD Deficiency: A Rare but Serious Risk
A small percentage of people carry genetic variants that prevent their bodies from breaking down fluorouracil properly. The enzyme responsible for metabolizing more than 80% of fluorouracil is called DPD, and it’s encoded by the DPYD gene. People with complete DPD deficiency face a risk of severe, potentially fatal toxicity even from topical application, because the drug can accumulate to dangerous levels in the body. Symptoms of systemic toxicity include severe mouth sores, diarrhea, dangerously low white blood cell counts, and neurological problems.
People with partial DPD deficiency also carry increased risk, though the effects are generally less severe. The FDA has updated safety labeling to reflect these risks. If you have a family history of severe reactions to fluorouracil or related drugs, genetic testing can identify DPD deficiency before treatment begins. Most people metabolize the drug normally and use the cream without systemic problems, but this is worth discussing with your prescriber if you have any concerns.