Benzalkonium chloride (BZK) has become more accessible due to the COVID-19 pandemic. Herein, we report a case of subcutaneous injection of BZK as a suicide attempt. The patient was a 50-year-old female. The patient injected a 10% BZK solution subcutaneously into the dorsum of the left hand and cubital fossa as a suicide attempt. On admission, redness on the back of the left hand and induration in the cubital fossa were noted. We applied cooling and steroid ointment; however, redness and swelling worsened. On the 10th day, coagulated necrotic adipose tissue was widely observed under the skin, and debridement and local negative pressure wound therapy were performed. On the 29th day, the wound on her left back was partially sutured, the remaining skin defect was fixed with the artificial dermis, and local negative pressure wound therapy was applied. The scar healed, and we sutured the left cubital fossa wound. Subcutaneous injection of chemicals requires aggressive incision and debridement, even in patients with poor skin findings.