A collapsed lung, known medically as a pneumothorax, happens when air leaks into the space between your lung and chest wall. That trapped air presses against the lung from the outside, preventing it from expanding fully. The leak can come from damage to the lung itself, a wound through the chest wall, or, rarely, from gas-producing microorganisms in the chest cavity. The specific cause determines how serious it is and how likely it is to happen again.
Spontaneous Collapse Without Lung Disease
Some lungs collapse without any obvious injury or illness. This is called primary spontaneous pneumothorax, and it typically strikes young, tall, thin men between the ages of 15 and 35. The annual rate is 7.4 to 18 per 100,000 men and 1.2 to 6 per 100,000 women. Researchers believe that rapid chest growth during adolescent growth spurts can create small air-filled blisters, called blebs, on the surface of the lung. These blebs can rupture without warning, letting air escape into the chest cavity.
No one has pinpointed a single cause, but the known risk factors are consistent: smoking, being male, being tall and lean, and having a family history of pneumothorax. Smoking appears to increase risk substantially, likely by causing low-grade inflammation in the small airways that promotes bleb formation. Many people who experience this have no idea anything is wrong with their lungs until the moment it happens.
Lung Disease as a Trigger
When someone with an existing lung condition develops a collapsed lung, it’s classified as secondary spontaneous pneumothorax. This is generally more dangerous because the lungs are already compromised. COPD (chronic obstructive pulmonary disease) accounts for roughly 70% of these cases. The damaged, over-inflated air sacs characteristic of COPD are fragile and prone to rupture.
Other conditions that increase risk include cystic fibrosis, asthma, interstitial lung disease (a group of disorders that scar the lung tissue), and connective tissue diseases that affect the lungs. Infections can also play a role. COVID-19, for instance, has been documented as a cause of secondary spontaneous pneumothorax, likely because severe inflammation weakens the lung tissue enough to allow air to escape.
Physical Trauma to the Chest
Any force that breaches the chest wall or damages the lung can cause a traumatic pneumothorax. This breaks down into two broad categories.
Blunt trauma, most commonly from motor vehicle collisions, is the leading cause of chest injuries overall. The impact can fracture ribs, and those broken rib ends can puncture the lung like a jagged edge through a balloon. Even without a fracture, a strong enough blow can compress the chest so rapidly that the sudden pressure change tears lung tissue.
Penetrating trauma, such as a stab wound or gunshot, creates a direct opening between the outside air and the chest cavity. Air rushes in through the wound with each breath, collapsing the lung on that side. This type, called an open pneumothorax, requires immediate treatment because the lung cannot re-inflate as long as the opening remains.
Medical Procedures Gone Wrong
A collapsed lung is one of the most common complications of certain chest procedures, a category called iatrogenic pneumothorax. Thoracentesis, a procedure where a needle drains fluid from around the lungs, carries a well-documented risk. Before ultrasound guidance became standard, the rate of pneumothorax from thoracentesis ranged from 4% to 30%. With ultrasound, that risk drops significantly, with recent large studies reporting rates around 0.6%.
Other procedures that can accidentally puncture the lung include central line placement (inserting a catheter into a large vein near the collarbone), lung biopsies, and mechanical ventilation. In ventilated patients, the machine pushes air into the lungs under pressure, and if that pressure exceeds what weakened lung tissue can handle, a rupture can occur.
Pressure Changes During Flying and Diving
Rapid shifts in atmospheric pressure can trigger a collapse in people who have air-filled cysts or blebs in their lungs. The physics are straightforward: as outside pressure drops (during a flight’s ascent, for example), trapped air inside a bleb expands. Think of a sealed bag of chips puffing up at altitude. If the bleb wall can’t stretch enough, it bursts.
Scuba diving poses a similar risk, but the timing is different. During descent, increased water pressure actually compresses the cysts. The danger comes during ascent, when the surrounding pressure drops and the trapped air re-expands rapidly. Pulmonary barotrauma from diving can be especially serious. For anyone with a history of spontaneous pneumothorax or known lung cysts, these activities carry meaningful risk.
Catamenial Pneumothorax in Women
A rare but underdiagnosed cause of recurrent collapsed lungs in women is catamenial pneumothorax, linked to endometriosis affecting the chest. This typically happens within 24 to 72 hours of the start of a menstrual period. Several mechanisms have been proposed. Endometrial tissue may migrate from the uterus upward through the abdomen, eventually damaging the diaphragm and allowing air to pass into the chest cavity. Alternatively, endometrial cells may travel through the bloodstream or lymphatic system to the lining of the lung, where they break down during menstruation and create small holes. Another theory suggests that hormonal changes during the menstrual cycle cause small airways to constrict, building enough pressure to rupture delicate air sacs.
Because it’s rare and the symptoms mimic a standard spontaneous pneumothorax, catamenial pneumothorax is often missed for years. Women who experience repeated lung collapses timed to their menstrual cycle should raise this possibility with their care team.
Tension Pneumothorax: When It Becomes Life-Threatening
Most collapsed lungs are painful and require treatment, but tension pneumothorax is a true emergency. It occurs when the air leak acts like a one-way valve: air enters the chest cavity with each breath but can’t escape. Pressure builds continuously, compressing the heart and the opposite lung.
The signs are distinct from a standard collapse. Severe respiratory distress, dangerously low blood pressure, visibly distended neck veins, and absent breath sounds on one side of the chest all point to tension pneumothorax. In advanced cases, the windpipe shifts visibly toward the unaffected side as the mounting pressure displaces the structures in the center of the chest. Without rapid intervention, this condition can be fatal within minutes.
Recurrence Risk After a First Episode
One of the most important things to know after a collapsed lung is how likely it is to happen again. Recurrence rates vary significantly by age and treatment. In a large population study, teenagers between 14 and 19 had a 5-year recurrence rate of 29.2%, far higher than older age groups, which ranged from 4.5% to 11.9%. This likely reflects ongoing growth and the persistence of blebs in younger patients.
Interestingly, patients managed conservatively (observation and rest rather than surgery) had lower 5-year recurrence rates than those who underwent surgical treatment, at 7.9% versus 23.7%. That gap is partly explained by selection bias: surgery is typically reserved for the most severe or complicated cases, which are inherently more likely to recur. Still, a second episode is common enough that anyone who has had one collapsed lung should be aware of the symptoms and know that chest pain with sudden shortness of breath warrants immediate evaluation.