Subcutaneous emphysema happens when air gets trapped beneath the skin, and the causes range from chest trauma and surgery to dental procedures, mechanical ventilation, and certain infections. The trapped air produces a distinctive crackling sensation under the skin called crepitus, and while it often resolves on its own within a week or two, understanding the source of the air leak matters for proper treatment.
How Air Gets Trapped Under the Skin
Air doesn’t belong in the tissue layers beneath your skin, so its presence always signals that a barrier somewhere has been breached. The specific pathway depends on the cause, but in most cases the mechanism follows one of two patterns: air enters directly from outside the body through a wound or opening, or air escapes from an internal structure like the lungs or digestive tract and migrates outward through tissue planes.
When the lungs are involved, the process follows what’s known as the Macklin effect. It works in three steps: tiny air sacs in the lungs rupture, the escaped air tracks along the sheaths that surround blood vessels and airways inside the lung, and then it spreads into the central chest cavity and from there into the soft tissues of the neck, face, or chest wall. This is the mechanism behind most cases linked to chest injuries and mechanical ventilation.
Chest Trauma and Rib Fractures
Blunt chest trauma is one of the most common causes. A car accident, fall, or direct blow to the chest can fracture ribs, puncture lung tissue, or tear the airway. Any of these injuries can allow air to leak into surrounding soft tissue. Penetrating injuries, such as stab wounds or gunshot wounds to the chest or neck, create a more direct path for air to enter subcutaneous layers.
Facial bone fractures are another frequent source, particularly when the sinuses are involved. Fractures of the bones around the eye sockets, the upper jaw, or the forehead sinuses can push air from the sinus cavities into the soft tissue of the face and neck. These fractures sometimes produce dramatic facial swelling that can initially be mistaken for a more serious condition.
Surgery and Medical Procedures
Subcutaneous emphysema is a recognized complication of several medical procedures, and it’s one of the more common iatrogenic (medically caused) sources. Procedures that carry risk include endotracheal intubation (placing a breathing tube), chest surgery with chest tube placement, and laparoscopic surgery, which uses gas to inflate the abdomen for better visibility. During intubation, the lining of the airway can tear, allowing air to escape into the neck tissues. Improperly positioned chest tubes can also introduce air into the chest wall.
Dental Procedures
Dental work is a surprisingly common cause of subcutaneous emphysema in the face and neck. The vast majority of dental cases involve air-driven high-speed handpieces and air syringes, the tools dentists use for drilling, drying, and cleaning. These instruments generate pressurized air that can be forced through the gum tissue into the deeper fascial spaces of the face if the tissue barrier is disrupted.
Specific procedures linked to this complication include surgical tooth extractions, root canal treatment, crown preparation, dental implant placement, and even routine polishing with air-powder units. In one documented case, air entered the tissue simply through the gum pocket during a filling procedure when an air syringe was used near a site where the gum had been slightly separated from the underlying bone. Dental lasers with air cooling sprays and hydrogen peroxide irrigants pushed beyond a tooth’s root tip have also been reported as causes.
The risk is highest when air-driven tools are used near areas where the gum tissue has already been disrupted, creating a pathway for pressurized air to enter the soft tissue layers. Dental-related cases typically resolve within 3 to 5 days with conservative treatment, and most patients recover completely within 7 to 10 days.
Mechanical Ventilation and Barotrauma
Patients on mechanical ventilators face a 3% to 10% risk of developing barotrauma, which occurs when the positive pressure used to inflate the lungs exceeds what the lung tissue can tolerate. The excessive pressure ruptures the tiny air sacs, and the escaped air migrates through the Macklin effect pathway into the chest cavity and subcutaneous tissues.
Higher ventilator pressures increase the risk, and barotrauma has traditionally been associated with peak airway pressures above 35 cmH₂O. However, patients with already-damaged lungs can develop subcutaneous emphysema even at lower pressures. During the COVID-19 pandemic, cases were documented in patients ventilated at pressures well below the thresholds previously considered safe, likely because the underlying lung disease made the tissue more fragile. Protective ventilation strategies using lower volumes of air and carefully managed pressures help reduce this risk.
Infections That Produce Gas
Certain bacterial infections can produce gas within tissue, creating a form of subcutaneous emphysema that looks similar to air-leak cases on imaging but has a very different cause and urgency. Gas-forming infections include gas gangrene (caused by Clostridium bacteria) and other necrotizing soft tissue infections involving a mix of bacteria.
Distinguishing between these two causes matters enormously because gas gangrene is a surgical emergency. The key difference on imaging is where the gas appears: in air-leak emphysema, gas tracks along the tissue planes between muscles, while in gas gangrene, the gas is found within the muscle itself. During surgery, if the muscle tissue looks healthy and viable with no pus or tissue death, gas gangrene can essentially be ruled out, and the source is more likely a perforation of the gastrointestinal tract or another air-leak cause.
Other Causes
Barotrauma from activities outside the hospital can also trigger subcutaneous emphysema. Scuba diving is a classic example, where rapid changes in pressure can rupture lung tissue during ascent. Forceful coughing, vomiting, or straining during labor can generate enough pressure in the chest to cause small air sac ruptures, though this is uncommon. Swallowing or inhaling a foreign body that damages the airway or esophagus is another occasional cause.
How It’s Recognized
The hallmark of subcutaneous emphysema is crepitus: a crackling or popping sensation felt when pressing on the swollen skin. It’s often compared to the feel of bubble wrap under the skin. Visible swelling is usually present in the affected area, which can include the neck, chest wall, face, eyelids, scalp, or abdomen depending on where the air originated and how far it has traveled.
On a chest X-ray, trapped air appears as dark streaks within the soft tissue. A distinctive pattern called the ginkgo leaf sign can appear when air outlines the individual muscle fibers of the chest wall, creating a branching pattern that resembles the veins of a ginkgo leaf. CT scans provide a more detailed picture and help identify the underlying source of the air leak, which is critical for guiding treatment.
How the Body Clears Trapped Air
In most cases, the body gradually reabsorbs the trapped air on its own once the source of the leak is addressed. For uncomplicated cases like those from dental procedures, noticeable improvement typically happens within 3 to 5 days, with complete resolution in 7 to 10 days. More extensive cases, particularly those involving chest trauma or ventilator-related barotrauma, can take longer.
Breathing supplemental oxygen through a nasal cannula or mask can speed the process. It works by reducing the concentration of nitrogen in the blood, which creates a pressure gradient that draws nitrogen out of the trapped air pocket more quickly. Treatment also involves addressing whatever caused the air leak in the first place, whether that means repairing a lung injury, adjusting ventilator settings, or managing an infection. Antibiotics are commonly prescribed as a precaution against infection in the affected tissue, with an average course lasting about 8 to 9 days in studies of dental-related cases.