Salicylic acid

• There is evidence from a Cochrane systematic review, that salicylic acid administered daily for up to 12 weeks is more effective than placebo at clearing cutaneous warts, with a low likelihood of adverse effects. Limited trial data suggest that it is 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.

Cryotherapy with liquid nitrogen

• There is little evidence regarding the effectiveness of cryotherapy, and in particular there is no evidence to support the common view that cryotherapy is more effective than topical salicylic acid.
• Available evidence, from a Cochrane systematic review, suggests that more intense levels of freezing (that is, a longer duration of application of cold to the wart) are more effective than gentler freezing regimens; that treatment intervals of 2, 3, or 4 weeks are equally effective; and that treatment beyond 3 months is unlikely to give any additional benefit.
• There are limited data on adverse effects, but pain and blistering are commonly reported and seem to be more likely to occur with more frequent applications and more intense levels of freezing.

Contraindications to cryotherapy

• These recommendations are based on published expert opinion [Sterling et al, 2001; Andrews, 2004] and expert opinion from CKS reviewers.

Combining salicylic acid and cryotherapy

• There is limited evidence for this approach [Gibbs and Harvey, 2006], and there is uncertainty regarding the best regimen to use when combining these treatments.
• Specialists use various approaches to alternating salicylic acid and cryotherapy, over differing timescales.
• Most CKS expert reviewers agreed that combination therapy is appropriate in primary care and that it may be useful to use the topical treatment once the scabbing from cryotherapy has resolved.

Duct tape

• There is limited evidence that occlusion with duct tape is effective for treating warts. There is weak evidence from one small randomized controlled trial (RCT) (n = 51) that occlusion with duct tape may be an effective treatment for warts. However data from two subsequently published larger trials (n = 90, n = 103) do not support this conclusion.
• Adverse effects were infrequent in adults. In one trial, 15% of children who were treated with duct tape experienced erythema, eczema, and wounds but this finding was not statistically significant.

Cryotherapy for younger children

• Cryotherapy is not recommended because younger children may find it too painful and may not be able to keep still long enough for the treatment to be applied.

Cryotherapy with over-the-counter freeze spray

• There is weak evidence from one small (n = 124) RCT that dimethyl ether/propane (DE-P) has equivalent efficacy to liquid nitrogen for the treatment of warts [Caballero Martinez et al, 1996]. However, this trial had a number of methodological problems making the results difficult to interpret.
• There are also concerns that DE-P (which evaporates at –57°C) does not reduce the tissue temperature enough to cause adequate cell necrosis [Sterling et al, 2001], although this has not been evaluated in RCTs. In comparison, liquid nitrogen reaches a much lower temperature when it evaporates (–196°C).

Silver nitrate

• Chemical cauterization with silver nitrate has been used for decades to treat cutaneous warts, however the evidence base to support its use is very limited. There is very weak evidence from two small trials (n = 70, n = 60) that silver nitrate is effective for treating warts. Both trials had methodological weaknesses, making the results difficult to interpret. Well-conducted RCTs are needed to confirm these results.
• Silver nitrate may cause chemical burns on the surrounding skin and black discolouration of the skin.
• Most CKS expert reviewers agree that silver nitrate should not be used.

Glutaraldehyde, formaldehyde, podophyllin, and podophylotoxin

• CKS found no placebo controlled RCTs that assessed the effectiveness of glutaraldehyde, formaldehyde, podophyllin, or podophylotoxin for the treatment of warts. However they may be used in secondary care.