Sodium hypochlorite (NaOCl) is currently used in the debridement and disinfection of the root canal system, supporting the mechanical procedures. Although it is considered a safe irrigant, the literature reports a few cases of adverse reaction caused by NaOCl: They range from injection through the apical foramen to air emphysema and allergic reactions as complications during endodontic treatment. The present report shows the possible severe clinical consequences of concentrated NaOCl extruding through the periapical tissues during root canal irrigation in a patient not allergic to NaOCl.