BACKGROUND: Liquid nitrogen (LN2) has been widely used in the treatment of warts. However, formic acid (FA), the keratolytic agent, has recently been introduced for the treatment of recalcitrant warts, such as palmoplantar or periungual warts. The efficacy of treatment varies depending on the location, size, number and type of wart, as well as the age and co-operation of the patient. OBJECTIVE: The aim of this study was to evaluate the efficacy and safety of FA and LN2 therapy for the treatment of warts. METHODS: Twenty-four patients with a total of 101 warts were treated with FA, and fifty-three patients with 248 warts were treated with LN2. In the FA-treated group, 85% FA was applied to the warts 2 to 7 times using a stick, according to the degree of response. In the LN2-treated group, LN2 was applied with the sustained 10-s freeze technique using a cotton tip. Treatment with FA was administered weekly, whereas treatment with LN2 (with 2 freeze thaw cycles) was administered in 2 week intervals. Treatment effectiveness was assessed when the complete clearance of warts had occurred or after 12 weeks of treatment. RESULTS: Complete clearance of warts occurred in 30.7% (31/101warts) of the FA-treated group, and 47.2% (119/248warts) of the LN2 treated group. Cryotherapy with LN2 was more effective than FA in the cure rate (p=0.001). In the FA-treated group, 11 patients reported adverse effects such as pain, stinging and erythema, however it was generally found to be tolerable and transient. In addition, 10 patients reported hyperpigmentation. In the LN2 group, 38 patients experienced mild- to-moderate vesicle formation and 9 patients reported hypopigmentation. CONCLUSION: This study shows that cryotherapy with LN2 is more effective than FA in the treatment of recalcitrant warts. However, LN2 causes a significantly greater morbidity in terms of pain and blistering. FA is an effective and safe alternative treatment, so can be considered for patients who are intolerable to pain.
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