Squaric acid is a form of topical sensitization therapy in which delayed -type hypersensitivity reaction develops at the site of the wart . Side effects include contact dermatitis and rarely hives. Multiple applications are necessary to generate an appropriate immune response. Since therapy with squaric acid is painless, it is often preferred by younger patients. Squaric acid is useful in patients with large numbers of warts and several studies have demonstrated excellent response rates8