Treatment of alopecia areata with squaric acid dibutylester

Squaric acid dibutylester is a topical sensitizing agent utilized for the treatment of alopecia areata. The mechanism of action is not fully understood, but is believed to redirect the inflammatory response by invoking allergic contact dermatitis. Several studies have compared the efficacy of squaric acid dibutylester to other treatments vs placebo with favorable results. This contribution reviews the history of the topical sensitizing agent squaric acid dibutylester and discusses the mechanism of action, the use in alopecia areata, and the efficacy and safety of this therapeutic agent.