A lung collapses when air leaks into the space between the lung and the chest wall, or when something blocks an airway and prevents air from reaching part of the lung. These are two distinct problems. When air enters the space surrounding the lung (called the pleural space), the pressure pushes inward and the lung deflates, a condition known as pneumothorax. When an airway gets blocked and the tiny air sacs beyond the blockage gradually empty, that partial collapse is called atelectasis. Both result in less working lung tissue, but they happen for very different reasons.
How a Lung Actually Collapses
Your lungs stay inflated because of a pressure balance. The space between your lung and your rib cage has slightly lower pressure than the air inside your lungs, which keeps the lung tissue pulled open against the chest wall. If anything disrupts that balance, the lung can partially or fully deflate.
In pneumothorax, air gets into that surrounding space and equalizes the pressure, so the lung has nothing holding it open. Think of it like a vacuum seal breaking. In atelectasis, the airways themselves get plugged or compressed, and the air already in the blocked section slowly absorbs into the bloodstream with no fresh air coming in to replace it. The affected portion shrinks down like a deflated balloon.
Spontaneous Collapse Without Injury
Some lungs collapse with no obvious trigger. This is called a spontaneous pneumothorax, and it tends to follow a specific pattern. It most commonly affects tall, thin young men, often between ages 15 and 35. The combination of a lean body type and height creates more negative pressure at the top of the lung, which can cause small air-filled blisters (called blebs) to form on the lung surface. When one of these blisters ruptures, air escapes into the pleural space and the lung partially deflates.
Smoking significantly increases the risk. Even in otherwise healthy young people, cigarette smoke damages the lung tissue in ways that make these blisters more likely to form. Low body weight and caloric restriction also appear to be contributing factors, though the exact mechanism isn’t fully understood.
One concerning aspect of spontaneous collapse is the recurrence rate. In a study of 253 patients with a first-time spontaneous pneumothorax, just over half experienced it again, with 37% of those recurrences happening within the first year.
Collapse From Existing Lung Disease
When someone already has a chronic lung condition, the weakened tissue is more vulnerable to developing holes or tears. This is called secondary spontaneous pneumothorax, and it tends to be more dangerous because the lungs are already compromised. Conditions that increase the risk include COPD, emphysema, cystic fibrosis, asthma, tuberculosis, pneumonia, lung cancer, and pulmonary fibrosis. In these diseases, the lung tissue is either chronically inflamed, scarred, or structurally fragile, making a spontaneous air leak much more likely.
Trauma and Medical Procedures
A direct blow to the chest, a car accident, a stabbing, or a gunshot wound can puncture the lung or the chest wall, allowing air into the pleural space. This is traumatic pneumothorax, and it’s one of the most common chest injuries seen in emergency rooms.
Medical procedures can also cause it. Any time a needle is inserted into the chest, whether for a biopsy, to place a central IV line, or to drain fluid, there’s a small risk of accidentally puncturing the lung. Mechanical ventilation poses a particular danger because the machine pushes air into the lungs under pressure. If that pressure becomes unbalanced, the lung can collapse completely. This is one of the more severe forms and requires immediate treatment.
Blocked Airways and Partial Collapse
Atelectasis, the other type of lung collapse, happens when something prevents air from flowing into a section of the lung. The most common culprit is a mucus plug, a thick buildup of mucus that blocks an airway. This frequently occurs after surgery, when pain and anesthesia make it harder to cough and take deep breaths, allowing mucus to accumulate.
Tumors growing inside an airway can also narrow or block it, causing the air sacs beyond the blockage to gradually deflate. In children, a common cause is inhaling a small object like a peanut or a toy piece that lodges in a bronchial tube. External compression from fluid buildup around the lungs or from an enlarged lymph node pressing on an airway can produce the same result.
What a Collapsed Lung Feels Like
The hallmark symptom is a sudden, sharp chest pain on one side, often accompanied by shortness of breath that comes on within minutes. The pain typically worsens with breathing. Your heart rate and breathing rate may both increase noticeably. In more severe cases, blood pressure drops, oxygen levels fall, and the windpipe can shift visibly toward one side of the neck. That last sign, called tracheal deviation, points to a tension pneumothorax, which is the most dangerous form because the trapped air keeps building pressure and compresses the heart and the unaffected lung.
Atelectasis tends to develop more gradually and may cause mild shortness of breath or a low-grade fever rather than the dramatic, sudden symptoms of pneumothorax. Small areas of atelectasis sometimes produce no symptoms at all and are found incidentally on a chest X-ray.
Recovery and Long-Term Considerations
A small pneumothorax may resolve on its own as the body reabsorbs the leaked air over days to weeks. Larger collapses typically require a tube inserted through the chest wall to drain the air and allow the lung to re-expand. Recovery after treatment generally takes one to two weeks for a straightforward case, though returning to full activity may take longer.
The high recurrence rate means lifestyle adjustments matter. Flying in a commercial airplane is generally discouraged until the pneumothorax has fully resolved and been confirmed on imaging, because the lower cabin pressure at altitude can cause residual air to expand. The restrictions on scuba diving are far more permanent. Most dive medicine specialists recommend that anyone who has had a spontaneous pneumothorax stop diving entirely. At depth, pressure changes are extreme, and the risk of a tension pneumothorax underwater, where emergency treatment isn’t available, is considered too dangerous regardless of how much time has passed since the original event.
For atelectasis, recovery depends on addressing the underlying blockage. Post-surgical cases usually improve with deep breathing exercises, coughing, and getting up and moving. Cases caused by tumors or chronic conditions require treatment of the root problem.