Fluorouracil cream: what it treats, how to take it, side effects
Last updated September 3, 2026.
Fluorouracil cream (brand name Efudex) is a prescription chemotherapy cream that destroys precancerous and superficial cancerous skin cells. It treats actinic keratoses, the rough sun-damage spots that can turn into skin cancer, and some superficial basal cell carcinomas.
What does it treat?
It treats actinic (solar) keratoses, scaly or crusted lesions from years of sun exposure, and superficial basal cell carcinoma when the usual treatments cannot be used. It works by killing fast-growing cells, which is why the treated skin goes through an ugly phase before it heals healthier than before.
How do you take it?
Apply a thin layer to the affected areas twice a day, at about the same times each day, using a glove or washing hands immediately after. A typical course for actinic keratoses runs 2 to 4 weeks, and your doctor tells you when to stop based on the reaction. Expect the spots to get red, raw, and crusted before they improve; that is the drug working, and full healing can take 1 to 2 months after the last application. Keep the cream off the eyes, mouth, and mucous membranes, and protect treated skin from sunlight, which intensifies the reaction. Missed dose: apply when remembered unless the next dose is near.
Side effects to know
- Common: the expected local reaction: redness, burning, pain, erosion or crusting, and peeling at the treated spots, plus high sun sensitivity during treatment.
- Serious: severe, widespread reactions in people with DPD enzyme deficiency (who cannot break down the drug), allergic reactions, and eye exposure. Ulcerated, weeping skin that spreads well beyond the treated spots needs a call to your doctor.
Who should not take it?
Do not use fluorouracil cream if you are pregnant or may become pregnant; it can harm a fetus, and that warning is in the label. Tell your doctor if you have DPD enzyme deficiency, which makes even topical use dangerous. It is for skin only, never eyes, mouth, or vagina. During treatment, avoid tanning beds and prolonged sun, and cover up outdoors. Breastfeeding is a doctor conversation.
When is it an emergency?
Call 911 for swelling of the face, lips, or throat or trouble breathing after applying. Severe pain, spreading ulceration, fever, or a reaction covering large areas also needs urgent care, especially with any chance of DPD deficiency. Pymander's escalation routing is built and tested specifically for this class of decision; see the safety architecture working paper.
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Common questions
Why does my skin look worse during treatment?
That is the mechanism. Fluorouracil kills fast-growing cells, and precancerous spots are full of them, so they redden, erode, and crust before they slough off. Dermatologists use that visible reaction to judge when to stop. New skin forms over the following 1 to 2 months.
How long does a course of fluorouracil cream last?
For actinic keratoses, typically 2 to 4 weeks of twice-daily application, with your doctor adjusting by how your skin responds. Superficial basal cell carcinoma courses run longer, often 3 to 6 weeks or more, only at the 5% strength.
Can I wear makeup or moisturizer over it?
Let the cream absorb fully first, then plain moisturizer is usually fine and often recommended for the raw phase. Makeup can wait until your dermatologist says the reaction has settled; layering products on actively eroding skin stings and can trap the medication where it should not linger.
What is DPD deficiency and why does it matter?
DPD is the enzyme that breaks down fluorouracil. People lacking it can develop severe, even life-threatening toxicity from the drug, and MedlinePlus directs patients to tell their doctor about it before starting. It is rare, but if you or family members have reacted severely to chemotherapy, say so.
Can I use fluorouracil cream while pregnant?
No. The label warns it may cause fetal harm, and MedlinePlus directs patients to avoid pregnancy during use and call the doctor immediately if pregnancy happens mid-treatment. Alternatives for actinic keratoses can wait or be chosen differently during pregnancy.
Do I really need to avoid the sun during treatment?
Yes. The drug makes treated skin markedly more sun-sensitive, and sunlight intensifies the inflammation beyond the useful reaction. Cover the area, use sunscreen on surrounding skin, and skip tanning entirely until your dermatologist clears you.