A lung collapses when air leaks into the space between the lung and the chest wall, forcing the lung to deflate. This condition, called a pneumothorax, affects between 7 and 18 per 100,000 men and 1 to 6 per 100,000 women each year. The causes range from a sudden rupture of a tiny air blister on the lung surface to a traumatic injury like a broken rib. A lung can also partially collapse when an airway gets blocked and the air sacs beyond the blockage deflate, a separate condition called atelectasis.
How a Lung Actually Collapses
Your lungs don’t inflate on their own. They expand because the pressure in the thin space between the lung and chest wall (the pleural space) is lower than the pressure inside the lung. This negative pressure acts like a vacuum, pulling the lung open every time your chest wall expands. When air enters that pleural space, it equalizes the pressure, and the lung’s natural elasticity causes it to recoil inward and shrink. The more air that leaks in, the more the lung deflates.
Spontaneous Collapse Without Injury
Sometimes a lung collapses with no obvious trigger. This is called a spontaneous pneumothorax, and it happens when a small blister (called a bleb) on the surface of the lung ruptures, letting air escape into the pleural space. In otherwise healthy people, this is known as a primary spontaneous pneumothorax. It’s most common in tall, thin young men, likely because rapid chest growth during adolescence makes these blisters more likely to form. Long-term smoking significantly raises the risk in both men and women.
When someone already has an underlying lung disease, a spontaneous collapse is classified as secondary. The conditions most often responsible include COPD, cystic fibrosis, asthma, and interstitial lung disease. These diseases weaken lung tissue over time, making it more prone to rupture. Secondary spontaneous pneumothorax tends to be more serious because the lungs are already compromised.
Vaping has also been linked to lung collapse. Clinical reports of vaping-associated lung injury have documented pneumothorax as a complication, though it remains less studied than smoking-related cases.
Trauma to the Chest
Any force that damages the chest wall or punctures the lung can cause it to collapse. The most common scenarios are motor vehicle accidents and falls from height, which can fracture ribs. When a broken rib punctures the membrane surrounding the lung, air rushes into the pleural space. Stab wounds, gunshot wounds, and other penetrating injuries can do the same thing directly.
Rib fractures in the middle zone of the chest are particularly associated with lung collapse because of their proximity to the lung tissue. Even without a visible wound, blunt force can cause enough internal damage to tear the lung surface.
Medical Procedures That Can Cause Collapse
Lung collapse is a recognized complication of several routine medical procedures. Thoracentesis, a procedure where a needle drains fluid from around the lungs, is performed in up to 173,000 cases per year in the United States, and pneumothorax is its most common complication. Lung biopsies, central line placements in the neck or upper chest, and mechanical ventilation can all accidentally introduce air into the pleural space. These are called iatrogenic pneumothoraces, meaning they result from medical care rather than disease or injury.
Blocked Airways and Deflated Air Sacs
Not all lung collapse involves air leaking into the pleural space. Atelectasis occurs when something blocks an airway and the tiny air sacs beyond the blockage absorb their remaining air and deflate. The most common culprits are mucus plugs, which can form after surgery, during severe asthma attacks, or in people with cystic fibrosis. A tumor growing inside an airway, whether cancerous or not, can also narrow or block the passage enough to cause collapse.
In children, a common cause is inhaling a foreign object like a peanut or a small toy part. The object lodges in a bronchial tube and seals off the section of lung beyond it. Atelectasis also develops in people with respiratory weakness who can’t take deep enough breaths to keep all areas of the lung inflated, such as after abdominal or chest surgery.
Tension Pneumothorax: The Emergency
Most pneumothoraces are painful but not immediately life-threatening. A tension pneumothorax is the exception. This happens when the air leak works like a one-way valve: air enters the pleural space with each breath but can’t escape. Pressure builds continuously on the affected side. The traditional explanation is that this pressure physically pushes the heart and major blood vessels to the opposite side, cutting off blood flow. More recent research suggests the mechanism is more complex. The rising pressure causes widespread collapse of the remaining functional lung tissue, starves the blood of oxygen, and triggers a chain of events that increases resistance in the lung’s blood vessels and drops the heart’s output. This is a medical emergency that can cause cardiovascular collapse within minutes.
What Happens After a First Collapse
Treatment depends on severity. For a small, minimally symptomatic primary spontaneous pneumothorax, current British Thoracic Society guidelines support conservative management, meaning observation without intervention, regardless of the size of the collapse on imaging. If symptoms are significant, needle aspiration or a chest tube may be used to remove the trapped air and allow the lung to re-expand.
Recurrence is a real concern. Studies report recurrence rates for primary spontaneous pneumothorax ranging from about 8% to as high as 54% within the first four years, with most repeat episodes happening in the first six months. One surgical study found that 26% of patients experienced a second collapse, and 94% of those recurrences happened within six months of the first event. For secondary spontaneous pneumothorax, recurrence rates are even higher, ranging from 23% to 47%. When someone has repeated collapses, a surgical procedure to seal the lung surface or remove the blisters responsible is typically considered to prevent further episodes.