[2] In a minority of cases, a one-way valve is formed by an area of damaged tissue, and the amount of air in the space between chest wall and lungs increases; this is called a tension pneumothorax.

[5] Other conditions that can result in similar symptoms include a hemothorax (buildup of blood in the pleural space), pulmonary embolism, and heart attack.

[3] In a larger pneumothorax, or if there is shortness of breath, the air may be removed with a syringe or a chest tube connected to a one-way valve system.

[3] A primary spontaneous pneumothorax (PSP) tends to occur in a young adult without underlying lung problems, and usually causes limited symptoms.

[15][16] The most common findings in people with tension pneumothorax are chest pain and respiratory distress, often with an increased heart rate (tachycardia) and rapid breathing (tachypnea) in the initial stages.

Rarely, there may be cyanosis, altered level of consciousness, a hyperresonant percussion note on examination of the affected side with reduced expansion and decreased movement, pain in the epigastrium (upper abdomen), displacement of the apex beat (heart impulse), and resonant sound when tapping the sternum.

Deviation of the trachea to one side and the presence of raised jugular venous pressure (distended neck veins) are not reliable as clinical signs.

[24] Medical procedures, such as inserting a central venous catheter into one of the chest veins or taking biopsy samples from lung tissue, may also lead to pneumothorax.

Divers breathing compressed air (such as when scuba diving) may develop a pneumothorax as a result of barotrauma from ascending just 1 metre (3 ft) while breath-holding with their lungs fully inflated.

[13] Therefore, a pneumothorax can only develop if air is allowed to enter, through damage to the chest wall or to the lung itself, or occasionally because microorganisms in the pleural space produce gas.

[28] Chest-wall defects are usually evident in cases of injury to the chest wall, such as stab or bullet wounds ("open pneumothorax").

In secondary spontaneous pneumothoraces, vulnerabilities in the lung tissue are caused by a variety of disease processes, particularly by rupturing of bullae (large air-containing lesions) in cases of severe emphysema.

[15] In contrast, tension pneumothorax is a medical emergency and may be treated before imaging – especially if there is severe hypoxia, very low blood pressure, or an impaired level of consciousness.

[16][18] A plain chest radiograph, ideally with the X-ray beams being projected from the back (posteroanterior, or "PA"), and during maximal inspiration (holding one's breath), is the most appropriate first investigation.

[13] The size of the pneumothorax (i.e. the volume of air in the pleural space) can be determined with a reasonable degree of accuracy by measuring the distance between the chest wall and the lung.

[36][37] The treatment of pneumothorax depends on a number of factors and may vary from discharge with early follow-up to immediate needle decompression or insertion of a chest tube.

[12][15][19] Compared to tube drainage, first-line aspiration in PSP reduces the number of people requiring hospital admission, without increasing the risk of complications.

[46] Aspiration may also be considered in secondary pneumothorax of moderate size (air rim 1–2 cm) without breathlessness, with the difference that ongoing observation in hospital is required even after a successful procedure.

These are typically inserted in an area under the axilla (armpit) called the "safe triangle", where damage to internal organs can be avoided; this is delineated by a horizontal line at the level of the nipple and two muscles of the chest wall (latissimus dorsi and pectoralis major).

[15] Chest tubes are used first-line when pneumothorax occurs in people with AIDS, usually due to underlying pneumocystis pneumonia (PCP), as this condition is associated with prolonged air leakage.

[15] It is possible for a person with a chest tube to be managed in an ambulatory care setting by using a Heimlich valve, although research to demonstrate the equivalence to hospitalization has been of limited quality.

The results from VATS-based pleural abrasion are slightly worse than those achieved using thoracotomy in the short term, but produce smaller scars in the skin.

[12][15] Compared to open thoracotomy, VATS offers a shorter in-hospital stays, less need for postoperative pain control, and a reduced risk of lung problems after surgery.

[15] VATS may also be used to achieve chemical pleurodesis; this involves insufflation of talc, which activates an inflammatory reaction that causes the lung to adhere to the chest wall.

[15] For newborn infants with pneumothorax, different management strategies have been suggested including careful observation, thoracentesis (needle aspiration), or insertion of a chest tube.

Significantly above-average height is also associated with increased risk of PSP – in people who are at least 76 inches (1.93 meters) tall, the AAIR is about 200 cases per 100,000 person-years.

[52] The risk of contracting a first spontaneous pneumothorax is elevated among male and female smokers by factors of approximately 22 and 9, respectively, compared to matched non-smokers of the same sex.

[52] In secondary spontaneous pneumothorax, the estimated annual AAIR is 6.3 and 2.0 cases per 100,000 person-years for males and females,[21][55] respectively, with the risk of recurrence depending on the presence and severity of any underlying lung disease.

[12] An early description of traumatic pneumothorax secondary to rib fractures appears in Imperial Surgery by Turkish surgeon Şerafeddin Sabuncuoğlu (1385–1468), which also recommends a method of simple aspiration.

[15][60] Prior to the advent of anti-tuberculous medications, pneumothoraces were intentionally caused by healthcare providers in people with tuberculosis in an effort to collapse a lobe, or entire lung, around a cavitating lesion.