Posttraumatic subcutaneous emphysema, which can be benign and noninfectious, is associated with necrotizing fasciitis. Rarely, extensive emphysema occurs after a minor traumatic injury. A 23-year-old man came to our hospital with extensive emphysema, ranging from the left hand to the axilla, after a minor injury. Necrotizing fasciitis was suspected. Based on the blood and imaging tests, necrotizing fasciitis was not actively suspected. He was admitted and observed for one day, and he was discharged the following day. The mechanism by which air can enter through a small injury is unclear, but the one-way ball-valve mechanism is the most commonly proposed explanation. The nontraumatic causes of non-infectious subcutaneous emphysema include insect bites, skin biopsies, and the use of shock absorbers. Since it developed from a minor wound, other mechanisms, aside from the one-way ball-valve, were possibly involved. Based on the imaging results of this case, the air was predominantly distributed in the subcutaneous tissue along the neurovascular bundle. The relatively sparse tissue likely caused the extensive subcutaneous emphysema. While evaluating post-traumatic subcutaneous emphysema, benign and noninfectious cases should be differentiated to prevent unnecessary therapeutic intervention.