Subcutaneous emphysema occurs when air gets into tissues under the skin covering the chest wall or neck. This can happen due to stabbing, gun shot wounds, other penetrations, or blunt trauma. Air can also be found in between skin layers on the arms and legs during certain infections, including gas gangrene.

Subcutaneous emphysema can often be seen as a smooth bulging of the skin. When a health care provider feels (palpates) the skin, it produces an unusual crackling sensation as the gas is pushed through the tissue.

This is a rare condition. When it does occur, possible causes include:

• Pneumothorax (collapsed lung)
• Ruptured esophagus
• Ruptured bronchial tube

Most of the conditions associated with subcutaneous emphysema are very severe and require hospitalization. Medical staff would already be involved in most cases.