# A-20 — Fluorouracil

The only chemotherapy agent in this register, and the cheapest effective treatment in it. Two to four weeks of a deliberately damaged face, on a label that publishes no efficacy figure at all.

- **Canonical:** https://www.30plusskin.care/actives/fluorouracil
- **Site:** 30+/SKIN — Skincare, published as a spec sheet.
- **Issue:** ISSUE NO. 13 / REV. 2026.10
- **Standing terms:** INDEPENDENT · AFFILIATE-FUNDED · NOT MEDICAL ADVICE

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## Datasheet

- **INN / INCI:** Fluorouracil
- **Also known as:** 5-FU
- **Family:** Cytotoxic antimetabolite
- **Molecular weight:** 130.08 g/mol
- **Layer reached:** EPIDERMIS
- **Prescription only:** yes
- **Evidence grade:** B
- **Controlled trials on file:** 0
- **Strength range recorded:** 2%–5%
- **Representative reference concentration:** 5%
- **Irritation (0–10):** 10
- **Onset:** 2–4 WK, THEN 1–2 MONTHS TO HEAL
- **Stability:** STABLE — CYTOTOXIC; FATAL TO PETS IF INGESTED

## Mechanism

The concentration marker is not a recommended dose or a claim that other strengths are untested. Compare the vehicle, indication and trial population.

Blocks thymidylate synthase, halting DNA synthesis in rapidly dividing cells. Applied across a field, it destroys the atypical keratinocytes of actinic damage — including the subclinical ones — which is why the therapeutic endpoint is visible erosion rather than the absence of a reaction.

## Measured endpoints

_None on file._

## Layering

- **Do not layer with:** Pregnancy — contraindicated, DPD enzyme deficiency — contraindicated, Occlusion, Mucous membranes, Ultraviolet exposure during and immediately after
- **Pairs with:** Nothing — it is used alone, as a course

## Notes

- Dosed to a tissue endpoint rather than a calendar: continue until the inflammatory response reaches the erosion stage, then stop. Usual duration two to four weeks.
- The reaction is unsightly during therapy and usually for several weeks after stopping, and complete healing may take one to two months.
- There is no clinical studies section on the label — no success rate, no comparator, no sample size. The evidence exists in the literature; none of it is on the box.
- Contraindicated in DPD enzyme deficiency, with one reported case of life-threatening systemic toxicity from the 5% topical cream.
- The label warns it may be fatal if ingested by pets, and to avoid residues on hands, clothing, carpeting and furniture. Nothing else in this register carries that warning.
- Irritation is scored at 10 because erosion is the intended endpoint, not a side effect to be minimised.

## Products in the register containing it

| No. | Product | Stance | Score | Document |
| --- | --- | --- | --- | --- |
| R-56 | Bausch Health Efudex | CONDITIONAL | 61/100 | /reviews/efudex-fluorouracil-review |

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## Elsewhere in the register

- [Review register](/reviews)
- [Active monographs](/actives)
- [Brand register](/brands)
- [Evidence register](/evidence)
- [The ledger](/ledger)
- [How we test](/how-we-test)
- [Agent guide](/llms.txt)
- [Sitemap](/sitemap.xml)

_SOURCE-BASED ASSESSMENTS. PUBLISHER PREFERENCES ARE IDENTIFIED SEPARATELY._