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Keratolytic — Warts / Psoriasis / Hyperkeratosis Pregnancy: §4.6, verbatim: 'Pregnancy The safety of Duofilm during human pregnancy has not been established. Studies in animals given salicylic acid orally demonstrated embryo toxicity at high doses. Duofilm is not recommended during pregnancy. Lactation Salicylates are excreted in human milk. Duofilm is not recommended during lactation. If used or administered during lactation, care should be taken to avoid contact with the breast area in order to avoid accidental ingestion by the infant.'

Salicylic Acid

Brand names: Duofilm (with lactic acid), Occlusal, Verrugon, Capasal (shampoo with coal tar)

Salicylic acid is a topical keratolytic used for hyperkeratotic skin conditions including warts, corns, calluses, psoriasis, acne and seborrhoeic scaling.

Adult dose

Dose: Warts and verrucae — apply a thin layer to the wart once daily. §4.2, verbatim: 'Adults, the elderly and children aged 2 years and over. Apply daily to the affected areas only.' and 'Duofilm should be applied to the wart once daily preferably at bedtime.' The amount is expressed qualitatively by the SPC, verbatim: 'A thin layer of Duofilm should be applied directly to the wart. Care should be taken to avoid the healthy surrounding skin.' SCOPE: this is the wart regimen of one UK wart paint (salicylic acid with lactic acid). This SPC states NO salicylic acid percentage and NO milligram quantity, so no concentration is published — the percentage-strength ladder this page previously carried is not supported by anything in this bundle. This page's psoriasis, hyperkeratosis and scalp-shampoo uses are NOT covered by this source and are not dosed here.
Route: Topical, to the wart only. §4.2: 'Apply daily to the affected areas only.' §4.3: 'Avoid applying to normal skin.' §4.4: 'Avoid exposure to healthy skin' and 'Avoid contact with eyes and other mucous membranes.'
Frequency: Once daily, preferably at bedtime. Duration, §4.2 verbatim: 'It is recommended that treatment continues until whichever of the following occurs first: • Warts have been treated for 12 weeks • The wart is completely cleared and the normal ridgelines of the skin have been restored. For warts, clinically visible improvement should occur in 1-2 weeks, but the maximum effect may be expected after 4-8 weeks. If warts persist beyond 12 weeks of treatment, the patient should be advised to consult their pharmacist or doctor.'
maxDose is blank because the SPC states no maximum quantity, no maximum number of applications and no maximum treated area as a dose ceiling; the practical limits it does give are a 12-week treatment duration (in the frequency field) and an area threshold, §4.4 verbatim (the source renders the superscript square-centimetre as 'cm 2'): 'Consider alternative treatments if warts cover a large area of the body (more than 5 cm 2 ) due to the potential risk of salicylate toxicity.' FULL METHOD, §4.2 verbatim: '1. The wart should be soaked in warm water for 5 minutes and dried thoroughly with a clean towel. 2. The surface of the wart should be rubbed with a nail file, pumice stone, emery board or coarse washcloth, with care taken not to cause bleeding. 3. A thin layer of Duofilm should be applied directly to the wart. Care should be taken to avoid the healthy surrounding skin. 4. The solution should be allowed to dry thoroughly. The wart should be covered with a plaster (dressing) if it is large or if it is on the foot to help penetration of ingredients.' EXCIPIENT AND FLAMMABILITY, §4.4 verbatim: 'This medicine contains 10%v/v ethanol in each application. It may cause burning sensation on damaged skin.' and §4.2: 'Due to the flammable nature of Duofilm, patients should avoid smoking or being near an open flame during application and immediately after use.' NO CONCENTRATION IS PUBLISHED because none appears anywhere in the fetched SPC — neither the product name nor §4.2 states a salicylic acid percentage, and a percentage must not be inferred. CAUTION GROUPS, §4.4: 'Duofilm is not recommended in patients with diabetes, circulatory problems or peripheral neuropathy except under the supervision of a doctor.'

Paediatric dose

Route: Topical — to the wart only
Frequency: Once daily, preferably at bedtime — the same regimen as adults
dosePerKg is null because this is a topical keratolytic applied to a lesion: §4.2 states no weight-based, body-surface-area or age-banded quantity, and gives one regimen for every age it covers — verbatim: 'Adults, the elderly and children aged 2 years and over. Apply daily to the affected areas only.' AGE LIMITS, §4.2 verbatim: 'Children: Children under the age of 12 years should be treated under supervision. Treatment of infants under the age of 2 years is not recommended.' VIRAL-ILLNESS CAUTION, §4.4 verbatim: 'Oral salicylates taken during or immediately after a viral illness have been associated with Reye's syndrome and hence there is a theoretical risk with topical salicylates. Therefore, use is not advised in children or teenagers during or immediately after chickenpox, influenza, or other viral infections.' No salicylic acid concentration is stated anywhere in the fetched SPC, so none is published for children either. Verify against a children's formulary.

Dose adjustments

Renal

Not stated — no renal-impairment dosing statement appears in any fetched section of this SPC (§4.2–§4.8). The only systemic-absorption caution is the area limit in §4.4: 'Consider alternative treatments if warts cover a large area of the body (more than 5 cm 2 ) due to the potential risk of salicylate toxicity.'

Hepatic

Not stated — no hepatic-impairment dosing statement appears in any fetched section of this SPC.

Dose independently re-sourced from UK Summary of Product Characteristics (SPC) via the eMC; US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — clinician-reviewed. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

  • [§4.3] 'Hypersensitivity to the active substances or to any of the excipients listed in section 6.1.'
  • [§4.3] 'Do not use on open wounds, irritated or reddened skin, or any area that is infected.'
  • [§4.3] 'Duofilm should not be used on the face, anogenital regions, moles, birthmarks, mucous membranes, warts with hair growing from them, red edges or an unusual colour.'
  • [§4.3] 'Avoid applying to normal skin.'
  • [§4.4 — a precaution rather than a contraindication] 'Duofilm is not recommended in patients with diabetes, circulatory problems or peripheral neuropathy except under the supervision of a doctor.'
  • [§4.4 — a precaution] 'Avoid contact with eyes and other mucous membranes. In case of accidental contact with the eyes or other mucous membranes, flush with water for 15 minutes.'
  • [§4.4 — a precaution] Not advised 'in children or teenagers during or immediately after chickenpox, influenza, or other viral infections' because of the theoretical Reye's syndrome risk with salicylates.

Side effects

  • [§4.8] Very common (skin and subcutaneous tissue disorders): 'Application site reaction, pruritus, burning sensation, erythema, scaling, dryness.'
  • [§4.8] Common: 'Rash' (immune system disorders) and 'Skin hypertrophy'.
  • [§4.8] Rare (post-marketing): 'Application site hypersensitivity including inflammation', 'Application site pain and irritation', 'Application site discoloration/skin discoloration' and 'Allergic dermatitis'.
  • [§4.8] 'Exposure to healthy skin can lead to application site blistering and skin exfoliation.'
  • [§4.4] Allergic contact dermatitis from an excipient — 'Duofilm contains colophony which may cause allergic contact dermatitis.'
  • [§4.4] Burning sensation on damaged skin from the 10% v/v ethanol content; 'Duofilm may cause eye irritation.'

Interactions

  • [§4.5] 'Topical Duofilm may increase the absorption of other topically applied medicines. Therefore, concomitant use of Duofilm and other topical medicines on the treated area should be avoided.'
  • [§4.5] 'As systemic exposure of topically applied Duofilm is low, interaction with systemically administered medicines is not anticipated.'

Monitoring

  • [§4.4] Watch for skin irritation — 'Duofilm may cause skin irritation. If undue skin irritation develops treatment should be discontinued.' §4.2 adds: 'Patients should be advised to consult a pharmacist or doctor if skin irritation develops.'
  • [§4.2] Review response against the stated timeline — clinically visible improvement in 1-2 weeks, maximum effect at 4-8 weeks, and referral if warts persist beyond 12 weeks of treatment.
  • [§4.4] Reassess treated area for salicylate-toxicity risk — 'Consider alternative treatments if warts cover a large area of the body (more than 5 cm 2 ).'
  • [§4.2] Prepare the lesion at each application — soak in warm water for 5 minutes, dry, and rub the surface down with a nail file, pumice stone, emery board or coarse washcloth without causing bleeding.
  • No laboratory or systemic salicylate monitoring is specified anywhere in the fetched sections of this SPC.

Clinical monograph

How it works

It softens and loosens the stratum corneum by reducing keratinocyte cohesion and dissolving intercellular cement, promoting desquamation of thickened or scaly skin.

Prescribing in practice

  • Avoid application to large surface areas, broken skin or mucous membranes because extensive absorption can cause salicylate toxicity, particularly in children.
  • Do not use on facial or anogenital warts, or on lesions in patients with peripheral arterial disease, diabetes or neuropathy without specialist advice.
  • Protect surrounding healthy skin, as preparations can cause irritation and chemical burns.

Monitoring

Routine monitoring is not required for localised use; review treatment response and local irritation at follow-up.

Counselling the patient

  • Apply only to the affected area and protect surrounding skin.
  • File down softened hard skin gently between applications.
  • Stop and seek advice if marked redness, soreness or bleeding occurs.

Evidence & guidelines

Topical salicylic acid is an established first-line keratolytic for cutaneous warts, supported by long-standing clinical use and systematic reviews.

Reference: NICE CKS Warts and Verrucae; Gibbs et al. Cochrane (2012) Treatments for cutaneous warts; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Related

Curated clinical cross-links plus same-class fallbacks.

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