Subcutaneous/surgical emphysema (SCE, SE) is when gas or air is in the layer under the skin.
Fractures of the facial bones with sinus involvement
Penetrating gunshot injuries of head & neck or chest
Penetrating trauma to gastrointestinal/respiratory systems
Anesthesia either during endotracheal/naso-tracheal intubation
Laparoscopy—tearing of the tracheal mucosa during intubation, increased pressure in the alveoli because of excessive ventilation pressure, improper chest tube placement during chest surgery, dental high speed hand pieces)