A spontaneous pneumothorax is a collapsed lung that happens without any injury or trauma. Air leaks from the lung into the space between the lung and the chest wall, causing the lung to partially or fully deflate. It affects roughly 18 per 100,000 men and 6 per 100,000 women each year, and it strikes most often in young adults between 15 and 40.
Primary vs. Secondary Types
There are two distinct forms, and the difference matters because they affect different people and carry different levels of risk.
Primary spontaneous pneumothorax (PSP) happens in people with no known lung disease. The typical profile is a young, tall, thin male. Despite the lungs appearing healthy on standard tests, imaging and tissue samples reveal small air-filled blisters (called blebs or bullae) on the lung surface in up to 77% of cases. When one of these weak spots ruptures, air escapes into the chest cavity.
Secondary spontaneous pneumothorax (SSP) occurs in people who already have a lung condition. COPD is the most common culprit, but it also develops alongside cystic fibrosis, asthma, tuberculosis, certain pneumonias, and interstitial lung diseases like pulmonary fibrosis. Because the lungs are already compromised, SSP tends to cause more severe symptoms and is harder to recover from.
How a Lung Bleb Forms and Ruptures
The weak spots on the lung surface don’t appear overnight. One leading explanation points to chronic mechanical stress: the lung’s outer surface rubs against the ribs with every breath, creating a visible compression mark (sometimes called a “rib line”) on the tissue. Over months and years, this repeated friction triggers low-grade inflammation that can thin the lung wall, forming a small blister. The apex of the lung, tucked tightly against the top of the rib cage, takes the most friction, which is why blebs cluster there.
Anything that creates a sudden spike in chest pressure can push a fragile bleb past its breaking point. Heavy lifting, forceful coughing, straining on the toilet, even blowing up a balloon all briefly compress the lungs against the ribs. Once a bleb ruptures, air flows into the space around the lung, and the lung begins to collapse under the shifting pressure.
Risk Factors
Smoking is the single biggest modifiable risk factor, and the numbers are dramatic. Smoking increases the risk of a first spontaneous pneumothorax roughly 9-fold in women and 22-fold in men, with a clear dose-response relationship: the more you smoke, the higher the risk. A man who smokes heavily throughout his life has about a 12% lifetime chance of experiencing a spontaneous pneumothorax, compared to roughly 0.1% for a man who never smokes.
Height plays a role too. Taller people have longer lungs, and the apex of a longer lung sits under greater mechanical stress. Being tall and thin is the classic body type for primary spontaneous pneumothorax, likely because the lung tissue stretches more relative to the surrounding chest wall.
A handful of genetic conditions raise risk significantly. Connective tissue disorders like Marfan syndrome and Ehlers-Danlos syndrome weaken the structural proteins throughout the body, including the lung. Birt-Hogg-Dubé syndrome, caused by a mutation in the FLCN gene, leads to lung cysts that are prone to rupture. This condition is inherited in an autosomal dominant pattern, meaning a single copy of the altered gene from one parent is enough to cause problems.
What It Feels Like
The hallmark symptom is a sudden, sharp chest pain on one side, often accompanied by shortness of breath. The pain typically starts without warning and may feel stabbing or tight. In a primary spontaneous pneumothorax, where the person’s lungs are otherwise healthy, the breathlessness can be mild if the collapse is small. In secondary cases, even a small amount of air in the chest cavity can cause significant distress because the lungs are already working at reduced capacity.
A physical exam often reveals reduced or absent breath sounds on the affected side and a hollow, drum-like sound when the chest is tapped. Heart rate frequently rises as the body tries to compensate for the lost lung function.
When It Becomes an Emergency
Most spontaneous pneumothoraces are uncomfortable but not immediately life-threatening. The exception is a tension pneumothorax, where air keeps entering the chest cavity but can’t escape. The trapped air builds pressure, compressing the heart and major blood vessels. This cuts off blood return to the heart, drops blood pressure, and can lead to cardiac arrest if untreated.
Warning signs of tension pneumothorax include rapidly worsening breathlessness, visibly swollen neck veins, a racing heart, bluish skin, and low blood pressure. The windpipe may shift visibly away from the affected side. This is a true emergency that requires immediate decompression, typically by inserting a needle into the chest wall to release the trapped air before a chest tube can be placed.
How It’s Treated
Treatment depends on how much of the lung has collapsed and how symptomatic you are.
- Observation: For a small primary spontaneous pneumothorax with minimal symptoms, the current British Thoracic Society guidelines support watchful waiting regardless of the size visible on imaging. The air often reabsorbs on its own over days to weeks, though you’ll need follow-up imaging to confirm the lung is re-expanding.
- Ambulatory management: Some centers now use small, portable chest valves that let you go home while the lung heals. This approach works best for primary cases in people who have reliable support at home and easy access to follow-up care.
- Needle aspiration or chest tube: When observation isn’t appropriate, either because symptoms are significant or the collapse is large, air can be drawn out with a needle or drained continuously through a tube inserted between the ribs. The tube stays in place until imaging confirms the lung has re-inflated and the air leak has sealed.
For secondary spontaneous pneumothorax, treatment tends to be more aggressive from the start because of the underlying lung disease. A chest tube is more commonly needed, and hospital stays are typically longer.
Recurrence Risk
One of the most important things to know about spontaneous pneumothorax is that it tends to come back. Published recurrence rates for primary spontaneous pneumothorax range from about 8% to 52% depending on the study and follow-up period. British Thoracic Society guidelines cite a recurrence risk as high as 54% within the first four years.
Most recurrences happen quickly. In one study tracking 68 patients, about 78% of recurrences showed up within three months of hospital discharge, and 94% within six months. Secondary spontaneous pneumothorax has similarly high recurrence rates, ranging from 23% to 47%.
If you’ve had a second episode, or if the lung fails to re-expand after initial treatment, surgery becomes the next step. The most common procedure is a minimally invasive operation (video-assisted thoracoscopic surgery) to remove the blebs and roughen the lung’s outer surface so it adheres to the chest wall. This dramatically reduces the chance of another collapse, bringing recurrence rates down to low single digits.
Reducing Your Risk After an Episode
Quitting smoking is the single most effective thing you can do to lower your chance of recurrence. Given the 9- to 22-fold increase in risk that smoking carries, stopping tobacco use meaningfully changes the odds. Avoiding activities that create extreme spikes in chest pressure, like scuba diving, is also standard advice after a spontaneous pneumothorax. Most guidelines recommend never diving again after an episode unless you’ve had definitive surgery, because the pressure changes underwater can trigger another collapse. Air travel is generally safe once the pneumothorax has fully resolved, though most physicians recommend waiting at least one to two weeks after confirmed re-expansion before flying.