There is evidence that salicylic acid preparations are more effective than placebo at clearing cutaneous warts, with a low likelihood of adverse effects. Limited trial data suggest that they are at least as effective as cryotherapy. There is insufficient evidence to recommend any particular salicylic acid preparation over another. Topical salicylic acid is a well-established treatment for warts.

• A Cochrane systematic review (search date: to March 2005) evaluated the evidence for local treatments for cutaneous, non-genital warts in healthy (immunocompetent) people [Gibbs and Harvey, 2006]. In general, the methodological quality of trials was poor. Thirteen trials of salicylic acid and other topical treatments were included in the review. Most trials evaluated the effectiveness of salicylic acid, with or without lactic acid. The treatment period varied from 6–12 weeks and assessment of outcome was normally at the end of the treatment period (that is, short-term follow up, which may have overestimated effectiveness, as recurrence due to inadequate clearance of the virus would be missed).
• Compared with placebo:
• Pooled data from five placebo-controlled trials (n = 322) found that salicylic acid was superior to placebo in terms of cure rate (defined as disappearance of the wart).
• Cure rate was 73% in the active group compared with 48% in the control group (relative risk [RR] of cure 1.6, 95% CI 1.16 to 2.23, p = 0.005).
• One person would be cured for every four people treated with salicylic acid (or another topical treatment) for a period of 6–12 weeks (NNT = 4, 95% CI 3 to 7).
• One placebo-controlled trial (n = 57) of children and adults with simple plantar warts was classified as being of high methodological quality.
• Intensive topical treatment was used, combining trichloroacetic acid crystals with 60% salicylic acid ointment applied under an occlusive dressing and left in place for 1 week before being changed.
• Outcome was assessed at 6 weeks and 6 months.
• At 6 weeks, the cure rate for active treatment was 66% compared with 18% for placebo treatment.
• At 6 months, the cure rate for active treatment was 83% compared with 54% for placebo treatment (RR for cure 1.54, 95% CI 1.05 to 2.27).
• Compared with cryotherapy:
• Two trials (n = 320) compared cryotherapy with topical salicylic acid and lactic acid on hand and foot warts. In one trial, cryotherapy was administered every week, and in the other trial every 3 weeks.
• Pooled data found no difference in efficacy (RR 1.04, 95% CI 0.88 to 1.22, p = 0.7).
• Other comparisons:
• The other seven trials compared different preparations of salicylic acid, or compared salicylic acid with other topical treatments such as glutaraldehyde and anthralin.
• The limited evidence from these trials failed to show a convincing advantage of any particular treatment over topical salicylic acid.
• Adverse effects:
• In general, adverse effects were not well-reported. In one trial of intensive topical treatment, one of the 29 participants in the active group developed cellulitis. Minor skin irritation was reported occasionally in some of the other trials, but generally no important adverse effects of topical salicylic acid were identified.
• Conversely, a postal survey of people who had recently used topical treatments for warts reported that 70% felt a burning sensation after application of salicylic acid, and 27% reported pain. Blistering was also reported by 14% of people, and bleeding was reported by a further 11% [Thomas et al, 2006].