Subcutaneous emphysema is a medical condition in which air or gas becomes trapped under the skin, most often in the chest, neck, or face. It can cause noticeable swelling and a crackling sensation when the area is touched, similar to the sound of crunching snow. While subcutaneous emphysema itself is often not life-threatening, it typically signals an underlying problem such as trauma, infection, or a complication from a medical procedure. Recognizing and managing this condition promptly is important to prevent severe outcomes like pneumothorax or airway obstruction. This article provides a clear, patient-friendly explanation of subcutaneous emphysema, including its causes, symptoms, diagnosis, treatment, and prevention. 

Subcutaneous emphysema is a descriptive term used to indicate that air, which normally stays within the lungs and airways, has found its way into the layer of fat and soft tissue just beneath the skin. This process may occur suddenly after trauma or develop gradually after certain medical procedures. In simple terms, it means that tiny air bubbles are trapped under the surface of the skin, creating a soft swelling and a distinctive crackling feel when touched. 

Clinically, doctors use the term to describe a sign rather than a disease itself—a warning signal that air has escaped from where it belongs. It can affect the chest, neck, face, or other areas, depending on the source of the leak. In mild cases, the condition causes little more than an odd sensation, but in more extensive cases, the trapped air can interfere with breathing or mask serious internal injuries. 

Subcutaneous emphysema differs from conditions like angioedema or infection-related swelling because of the presence of air, not fluid or inflammation. The air trapped under the skin can move along tissue planes, sometimes extending far from the original site of injury. Its discovery prompts clinicians to search for an underlying cause—such as a lung rupture, tracheal injury, or bowel perforation—to ensure no life-threatening complication is missed. 

Common sources of air include: 

• Respiratory system: Air leaks from the lungs or airways due to trauma or pneumothorax. 

• Gastrointestinal tract: Air escapes after a rupture or perforation. 

• Head and neck region: Dental work, facial trauma, or sinus surgery can introduce air. 

• Infections: Certain bacteria, such as Clostridium species, can generate gas during infection. 

Subcutaneous emphysema by itself is usually benign and resolves with time, but its importance lies in detecting and managing the underlying cause. 

Subcutaneous emphysema occurs across all age groups and genders but is more common in adults exposed to risk factors like trauma, surgical procedures, or mechanical ventilation. While its true incidence is not well defined, studies suggest it appears in up to 1% of mechanically ventilated patients. Spontaneous cases are relatively rare but have been reported in young, healthy individuals following intense coughing, vomiting, or exercise. 

Subcutaneous emphysema has several causes, broadly classified into traumatic, iatrogenic (medical procedure-related), infectious, and spontaneous categories. 

Traumatic causes: 

• Chest injuries (such as rib fractures that puncture the lung) 

• Facial or neck trauma 

• Barotrauma from blast injuries or scuba diving 

• Esophageal rupture (Boerhaave syndrome) 

Iatrogenic causes: 

• Mechanical ventilation using high airway pressures 

• Tracheostomy or endotracheal intubation 

• Chest tube insertion or removal 

• Dental procedures using air-driven tools 

• Laparoscopic surgery with CO₂ gas 

Infectious causes: 

• Gas-forming bacterial infections such as gas gangrene or necrotizing fasciitis 

• Dental abscesses or oral infections producing gas 

Spontaneous causes: 

• Spontaneous pneumomediastinum from severe coughing or asthma attacks 

• Valsalva maneuvers (forceful exhalation against a closed airway) 

Risk factors: 

• Chronic lung disease (COPD, asthma) 

• Recent surgery or trauma 

• Use of mechanical ventilation 

• Smoking 

• Poor dental hygiene (for oral infections) 

The pathophysiology of subcutaneous emphysema involves air escaping from its original source (lungs, airway, gastrointestinal tract, or bacteria) and spreading through the body’s connective tissue planes. 

1. Lung or airway injury: Ruptured alveoli release air that travels along bronchovascular sheaths into the mediastinum (the central chest compartment) and from there into the neck or chest wall. 

2. Esophageal perforation: Air and digestive gases escape into the mediastinum and subcutaneous layers. 

3. Infectious process: Gas-producing bacteria generate air that diffuses into nearby tissues. 

Because the subcutaneous tissue is loose and extends widely across the body, air can spread extensively, sometimes reaching the arms, abdomen, or thighs. In severe cases, this can cause striking facial swelling or airway compression. 

Subcutaneous emphysema can range from mild, barely noticeable swelling to severe disfigurement or respiratory distress. Most cases are painless, but patients may experience a feeling of tightness or pressure under the skin. 

Common symptoms include: 

• Painless swelling of the face, neck, or chest 

• Skin tightness or fullness 

• Voice changes or hoarseness 

• Difficulty swallowing or breathing (if air compresses the airway) 

• Facial distortion or puffiness 

Common signs include: 

• Crepitus: A crackling or popping sound when the skin is pressed 

• Swelling that may spread rapidly 

• Hamman’s sign: A crunching sound heard over the chest during each heartbeat (suggestive of air in the mediastinum) 

• Dyspnea or tachypnea: Shortness of breath or rapid breathing if a pneumothorax is present 

In severe cases, airway compromise or cardiovascular instability may develop, especially if accompanied by pneumothorax or gas-forming infections. 

Diagnosis of subcutaneous emphysema is based on a combination of physical examination and imaging studies. 

Clinical evaluation: 

A healthcare provider may identify the condition by the distinctive crepitus under the skin, combined with recent trauma, medical procedures, or infection. 

Imaging tests: 

• Chest X-ray: Shows streaks or pockets of air in the subcutaneous tissue. It also helps identify related conditions such as pneumothorax. 

• CT scan (Gold Standard): Provides detailed images showing the source and extent of air leakage. 

• Ultrasound: Reveals a “snowstorm” pattern indicating air beneath the skin, useful in emergency settings. 

Laboratory tests: 

• Complete blood count (CBC) to detect infection 

• Inflammatory markers such as CRP or procalcitonin 

• Arterial blood gases to assess oxygen and carbon dioxide levels 

Several conditions may resemble subcutaneous emphysema but differ in cause and characteristics: 

• Angioedema: Swelling from allergic reactions without crepitus. 

• Cellulitis: Warm, red, and tender skin from bacterial infection, usually without crackling. 

• Lipedema: Fat accumulation causing swelling, typically in the legs. 

• Necrotizing fasciitis: A severe infection that may produce gas and crepitus but involves significant pain and systemic illness. 

Treatment focuses on addressing the underlying cause, relieving symptoms, and preventing complications. 

General principles: 

• Identify and treat the source of air leakage. 

• Monitor breathing and airway patency. 

• Provide supportive care, as most mild cases resolve spontaneously. 

Airway management: 

• Early intubation or tracheostomy may be required if facial or neck swelling threatens the airway. 

• Fiberoptic intubation can help in difficult cases. 

Oxygen therapy: 

• High-flow oxygen accelerates nitrogen absorption and helps the body reabsorb trapped air. 

Drainage procedures: 

• Chest tube placement to relieve pneumothorax. 

• In severe cases, small skin incisions or subcutaneous drains may be used to release trapped air. 

Infection control: 

• Broad-spectrum antibiotics if a gas-producing infection is suspected. 

• Surgical debridement in cases of necrotizing fasciitis or gas gangrene. 

Monitoring and observation: 

• Continuous monitoring of respiratory rate and oxygen levels. 

• Repeat imaging if symptoms worsen. 

• Minimize ventilatory pressures in mechanically ventilated patients. 

Although many cases are mild, complications can be serious when air spreads rapidly or affects vital structures. 

• Airway obstruction from swelling in the neck or face 

• Tension pneumothorax 

• Pneumomediastinum or cardiac compression 

• Gas embolism (rare) 

• Infection of affected tissues 

• Cosmetic disfigurement or discomfort 

The outlook for subcutaneous emphysema depends on the cause and timely management. 

• Most cases related to trauma or procedures resolve within several days to weeks. 

• Severe cases linked to infections or delayed diagnosis can be life-threatening. 

• With appropriate management, the prognosis is generally favorable. 

Preventing subcutaneous emphysema involves minimizing risk during medical and surgical procedures and promptly managing underlying causes. 

Key preventive measures: 

• Use appropriate ventilator settings to avoid barotrauma. 

• Employ proper techniques during intubation and tracheostomy. 

• Avoid excessive insufflation pressures during laparoscopic surgery. 

• Recognize and treat pneumothorax early. 

• Use protective barriers during dental procedures. 

• Promptly repair airway or esophageal injuries. 

For most patients, subcutaneous emphysema resolves without lasting problems. However, monitoring is essential, especially in cases linked to trauma or infection. Patients should: 

• Follow up regularly with their healthcare provider. 

• Avoid activities that increase chest pressure (heavy lifting, forceful coughing). 

• Practice deep breathing exercises under guidance. 

• Seek medical care if swelling worsens or breathing becomes difficult. 

Support groups and educational resources can also help patients and families understand the condition and its recovery process. 

Subcutaneous emphysema is the presence of air beneath the skin, most often caused by trauma, infection, or medical procedures. While it can appear alarming, it is frequently a self-limiting condition. However, because it can indicate serious underlying problems such as pneumothorax or infection, prompt evaluation and management are crucial. With early diagnosis, careful monitoring, and appropriate treatment, most people recover fully and without complications. 

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2. Macklin CC. Transport of air along sheaths of pulmonic blood vessels from alveoli to mediastinum: clinical implications. Arch Intern Med. 1939;64(5):913-926. 

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4. Maunder RJ, Pierson DJ, Hudson LD. Arch Intern Med. 1984;144(7):1447-1453. 

5. Hollingsworth HM, et al. Spontaneous subcutaneous emphysema and pneumomediastinum: case series and review. Chest. 2019;156(4):e103-e110.