Introduction
Pneumothorax occurs when air enters the pleural space, the thin potential space between the lung and the chest wall, and that trapped air disrupts the normal pressure balance needed to keep the lung expanded. The immediate cause is therefore not simply “a collapsed lung,” but a specific physiological failure: the lung can no longer remain fully inflated because air has escaped from the airway or lung tissue, or because outside air has entered the chest cavity through an injury. The condition develops through distinct biological processes, and the main causes fall into several broad groups: spontaneous rupture of weakened lung tissue, chest trauma, medical procedures, underlying lung disease, and less common contributing factors that make air leakage more likely.
Biological Mechanisms Behind the Condition
Under normal conditions, the lungs are held open by a delicate balance between the elastic recoil of the lung tissue and the negative pressure within the pleural space. The pleura consists of two thin membranes: the visceral pleura covering the lung and the parietal pleura lining the chest wall. A small amount of lubricating fluid allows these layers to slide against one another while remaining closely apposed. Because the pleural space normally contains very little air, the lung stays expanded as the chest wall moves outward during breathing.
Pneumothorax develops when that sealed system is breached. Air can enter the pleural space from the lung itself, from the outside through the chest wall, or from internal structures after injury or disease. Once air accumulates, the pressure in the pleural space rises toward atmospheric pressure, reducing the negative pressure that keeps the lung inflated. The affected lung then partially or fully recoils inward. In severe cases, especially when a one-way valve mechanism allows air to enter but not escape, pressure can continue to rise and interfere with both lung expansion and cardiovascular function.
The biological basis of pneumothorax depends on the integrity of alveoli, small airways, pleura, and chest wall structures. If fragile air sacs rupture, if the pleural membranes are torn, or if abnormal connections form between the airways and pleural space, air escapes where it should not. This makes pneumothorax fundamentally a disorder of structural failure and pressure imbalance rather than of simple breathing weakness.
Primary Causes of Pneumothorax
Spontaneous rupture of small air blisters or blebs is one of the most common causes, especially in otherwise healthy people. Subpleural blebs are small collections of air between the lung surface and the visceral pleura, while bullae are larger air spaces formed by tissue weakness and destruction. When one of these structures ruptures, air escapes from the lung into the pleural space. This can happen without obvious external injury because the tissue covering these air pockets is thin and vulnerable to pressure changes during deep breathing, coughing, straining, or even ordinary exertion.
Chest trauma is another major cause. Blunt trauma from a motor vehicle collision, fall, or impact can tear lung tissue, fracture ribs that puncture the pleura, or suddenly compress the chest enough to force air out of the airways and into the pleural space. Penetrating trauma, such as a stab wound or gunshot injury, can directly open the chest wall and allow external air to enter. In these cases, pneumothorax arises because the protective barrier separating the atmosphere from the pleural cavity is physically disrupted.
Barotrauma can also trigger pneumothorax. This occurs when pressure differences become large enough to rupture alveoli. Mechanical ventilation, especially with high airway pressures or high positive end-expiratory pressure, can overdistend fragile alveoli and cause air leakage. Similar pressure-related injury may occur during scuba diving or rapid ascent, when changing ambient pressure causes gas expansion in the lungs. The mechanism is straightforward: if air trapped in a region of the lung expands faster than the lung tissue can accommodate, microscopic tears can develop and allow air to escape.
Underlying lung disease is a major driver of secondary pneumothorax. Diseases that destroy lung tissue, create abnormal air spaces, or inflame and weaken the pleura increase the chance of rupture. Chronic obstructive pulmonary disease, for example, can form bullae that are prone to breaking. Necrotizing infections, severe asthma exacerbations, cystic lung disorders, and interstitial lung diseases may also alter tissue structure enough to permit air leakage. In these settings, the lung is already mechanically compromised, so even modest stress can produce a tear.
Medical procedures may inadvertently introduce air into the pleural space. Central venous catheter placement, lung biopsy, thoracentesis, positive-pressure ventilation, and certain thoracic surgeries can damage the pleura or lung surface. When this happens, air from the lungs or from the atmosphere can enter the pleural cavity through a temporary or persistent defect. The procedure itself is not the underlying disease; rather, it creates a pathway for air where none should exist.
Contributing Risk Factors
Several factors do not directly cause pneumothorax on their own but increase the likelihood that a rupture or air leak will occur. Genetic influences are important because inherited conditions can alter connective tissue or lung architecture. Disorders such as Marfan syndrome, Ehlers-Danlos syndrome, and Birt-Hogg-Dubé syndrome can weaken structural support in the lung or pleura. When connective tissue is abnormal, blebs, cysts, or fragile pleural surfaces may form more easily, increasing the chance of spontaneous air leak.
Environmental exposures can contribute by damaging lung tissue over time. Tobacco smoke is a major example, because smoking promotes inflammation, airway injury, and formation of apical blebs near the lung surface. Inhaled irritants and chronic particulate exposure can produce similar, though usually less dramatic, structural damage. Repeated inflammatory stress makes the pleura and adjacent lung tissue more susceptible to tearing.
Infections may also raise risk. Severe pneumonia, tuberculosis, and certain fungal infections can create cavities, necrosis, or air leaks in the lung. When infection destroys tissue integrity, the boundary between alveoli and pleural space becomes less secure. A weakened area may rupture under normal respiratory pressure. Infection-related pneumothorax reflects the destructive effect of inflammatory and necrotic processes on lung architecture.
Hormonal changes are thought to play a role in some forms of pneumothorax, particularly catamenial pneumothorax, which is linked to the menstrual cycle. In that setting, ectopic endometrial tissue in or near the diaphragm and pleura may respond to hormonal fluctuations, creating diaphragmatic defects or pleural air leaks. The mechanism is not identical to standard spontaneous pneumothorax, but it shows how cyclic hormonal influence can affect thoracic structures.
Lifestyle factors influence the mechanical stress placed on the chest and lungs. Smoking is the clearest example, but high-risk activities such as diving, flying in unpressurized settings, or repeated intense straining can also contribute in susceptible people. These factors matter because they alter pressure gradients across the lung and pleura, sometimes enough to expose a pre-existing weakness.
How Multiple Factors May Interact
Pneumothorax often develops through the interaction of several biological stresses rather than a single isolated event. A person with small apical blebs may never have symptoms until smoking-related inflammation weakens the surrounding tissue, a coughing episode raises intrathoracic pressure, and one bleb finally ruptures. In another person, a genetic connective tissue disorder may create structurally fragile lung surfaces, while a minor trauma or routine physical strain provides the final mechanical trigger.
These interactions occur because lung integrity depends on both tissue strength and pressure control. If the pleura is weakened, less force is required to create a leak. If airway pressures rise, the chance of rupture increases. If an underlying disease reduces the elastic stability of the lung, even ordinary breathing can become enough to uncover the defect. The result is a condition in which predisposing biology and immediate mechanical stress combine to produce air entry into the pleural space.
Variations in Causes Between Individuals
The causes of pneumothorax differ from one individual to another because the structural and physiological context is not the same in every person. Genetics can determine whether someone is born with a tendency toward abnormal connective tissue, cyst formation, or fragile pleura. Age also matters: younger people who develop pneumothorax often have primary spontaneous disease related to blebs or body habitus, while older adults more often have secondary pneumothorax due to chronic lung disease. The same event may therefore mean different things biologically depending on the patient’s age group.
Health status is another key variable. A person with emphysema, interstitial fibrosis, or a history of thoracic surgery has a very different baseline lung structure from someone with healthy lungs. Environmental exposure further modifies risk. Smoking history, occupational inhalation exposure, recurrent respiratory infections, and exposure to pressure changes all influence how stable the pleura and lung tissue are at the moment a rupture occurs. In practice, pneumothorax reflects the balance between vulnerability and stress, and that balance differs widely among individuals.
Conditions or Disorders That Can Lead to Pneumothorax
Several medical conditions are closely associated with pneumothorax because they damage the lung or pleura in specific ways. Chronic obstructive pulmonary disease, especially emphysema, is a common cause of secondary pneumothorax. Emphysema destroys alveolar walls and forms enlarged air spaces that can rupture, particularly near the lung apex. The underlying problem is loss of tissue architecture, which lowers the threshold for air leakage.
Cystic lung diseases such as lymphangioleiomyomatosis, Langerhans cell histiocytosis, and certain hereditary cystic disorders can produce thin-walled air-filled spaces throughout the lung. These cysts are structurally unstable and may rupture into the pleural space. Because the lung surface is altered at multiple sites, the risk of recurrence can also be higher.
Asthma, especially when severe, may contribute through intense coughing, airway obstruction, and marked pressure swings during breathing. While asthma does not usually destroy lung tissue in the same way as emphysema, extreme air trapping can raise alveolar pressure enough to cause rupture.
Infectious lung disease, including tuberculosis and necrotizing bacterial pneumonia, can erode lung tissue and form cavities that break into the pleural space. The same is true for abscesses or invasive fungal infections in severely compromised patients. When infection destroys lung continuity, the pleura becomes vulnerable to direct breach.
Connective tissue disorders such as Marfan syndrome and Ehlers-Danlos syndrome also deserve attention because they affect the framework that supports lung expansion. Abnormal collagen or fibrillin weakens the architecture of the lung and pleura, making spontaneous rupture more likely. In some cases, a person may develop pneumothorax before the underlying condition is formally recognized.
Conclusion
Pneumothorax develops when air escapes into the pleural space and disrupts the pressure system that keeps the lung expanded. The main causes include spontaneous rupture of blebs or bullae, blunt or penetrating chest trauma, pressure-related injury, lung disease, and medical procedures that create an air leak. Additional risk factors such as smoking, genetic connective tissue disorders, infections, hormonal influences, and environmental pressure changes can increase susceptibility by weakening lung structure or raising mechanical stress on the pleura.
Understanding the causes of pneumothorax requires understanding both structure and pressure. The condition occurs when the barriers that normally contain air within the lungs fail, allowing air to enter a space that should remain sealed. Different individuals develop this failure for different reasons, but the underlying physiology is the same: a breach in the lung or chest wall allows air to accumulate where it interferes with normal expansion. That combination of tissue weakness and pressure imbalance explains why pneumothorax occurs and why its causes vary so widely from person to person.