It is most commonly caused by:

- Oesophageal rupture, for example in Boerhaave syndrome

- Asthma or other conditions leading to alveolar rupture

- Bowel rupture, where air in the abdominal cavity tracts up into the chest.

It has also been associated with:

- "Mycoplasma pneumoniae" pneumonia

- obesity

It can be induced to assist thoracoscopic surgery. It can be caused by a pulmonary barotrauma resulting when a person moves to or from a higher pressure environment, such as when a SCUBA diver, a free-diver or an airplane passenger ascends or descends.

In rare cases, pneumomediastinum may also arise as a result of blunt chest trauma (e.g. car accidents, fights, over pressure of breathing apparatus), while still evolving in the same fashion as the spontaneous form.

Pneumomediastinum is most commonly seen in otherwise healthy young male patients and may not be prefaced by a relevant medical history of similar ailments.

There are three types of tracheomalacia:

- Type 1—congenital, sometimes associated with tracheoesophageal fistula or esophageal atresia

- Type 2—extrinsic compression sometimes due to vascular rings

- Type 3—acquired due to chronic infection or prolonged intubation or inflammatory conditions like relapsing polychondritis

If the symptoms are severe enough, treatment may be needed. These range from medical management over mechanical ventilation (both continuous positive airway pressure (CPAP), or bi-level positive airway pressure (BiPAP) to tracheal stenting and surgery.

Surgical techniques include aortopexy, tracheopexy, tracheobronchoplasty, and tracheostomy. The role of the nebulised recombinant human deoxyribonuclease (rhDNase) remains inconclusive.

Pulmonary aspiration of acidic material (such as stomach acid) may produce an immediate primary injury caused by the chemical reaction of acid with lung parenchyma, and a later secondary injury as a result of the subsequent inflammatory response.

Risk factors for pulmonary aspiration include conditions which depress the level of consciousness (such as traumatic brain injury, alcohol intoxication, drug overdose, and general anesthesia). A decreased gag reflex, upper esophageal sphincter and lower esophageal sphincter tone, gastroesophageal reflux, full stomach, as well as obesity, stroke, and pregnancy can all increase the risk of aspiration in the semiconscious. Tracheal intubation or presence of a gastric tube (for example, a feeding tube) may also increase the risk.

Choking is the fourth most common cause of unintentional injury-related death in the US. Many episodes are not reported because they are brief and resolve without seeking medical attention. Among reported events, the majority of episodes (80%) occur among children younger than age 15, with fewer episodes (20%) among age 15 and older. The death rate from choking is low at most ages but increases starting around age 74. Choking due to a foreign object resulted in 162,000 deaths (2.5 per 100,000) in 2013, compared to 140,000 deaths (2.9 per 100,000) in 1990.

Laryngotracheal stenosis (Laryngo-: Glottic Stenosis; Subglottic Stenosis; Tracheal: narrowings at different levels of the windpipe) is a more accurate description for this condition when compared, for example to subglottic stenosis which technically only refers to narrowing just below vocal folds or tracheal stenosis. In babies and young children however, the subglottis is the narrowest part of the airway and most stenoses do in fact occur at this level. Subglottic stenosis is often therefore used to describe central airway narrowing in children, and laryngotracheal stenosis is more often used in adults.

Respiratory disease is a common and significant cause of illness and death around the world. In the US, approximately 1 billion "common colds" occur each year. A study found that in 2010, there were approximately 6.8 million emergency department visits for respiratory disorders in the U.S. for patients under the age of 18. In 2012, respiratory conditions were the most frequent reasons for hospital stays among children.

In the UK, approximately 1 in 7 individuals are affected by some form of chronic lung disease, most commonly chronic obstructive pulmonary disease, which includes asthma, chronic bronchitis and emphysema.

Respiratory diseases (including lung cancer) are responsible for over 10% of hospitalizations and over 16% of deaths in Canada.

In 2011, respiratory disease with ventilator support accounted for 93.3% of ICU utilization in the United States.

A Saber-sheath trachea is a trachea that has an abnormal shape caused by chronic obstructive pulmonary disease. The posterior area of the trachea increases in diameter while the lateral measurement decreases.

Choking is caused by an object from outside the body, also called a foreign body, blocking the airway. The object can block the upper or lower airway passages. The airway obstruction is usually partial but can also be complete.

Among children, the most common causes of choking are food, coins, toys, and balloons. In one study, peanuts were the most common object found in the airway of children evaluated for suspected foreign body aspiration. Foods that pose a high risk of choking include hot dogs, hard candy, nuts, seeds, whole grapes, raw carrots, apples, popcorn, peanut butter, marshmallows, chewing gum, and sausages. The most common cause of choking death in children is latex balloons. Small, round non-food objects such as balls, marbles, toys, and toy parts are also associated with a high risk of choking death because of their potential to completely block a child's airway.

Children younger than age three are especially at risk of choking because they explore the environment by putting objects in their mouth. Also, young children are still developing the ability to chew food completely. Molar teeth, which come in around 1.5 years of age, are necessary for grinding food. Even after molar teeth are present, children continue developing the ability to chew food completely and swallow throughout early childhood. In addition, a child's airway is smaller in diameter than an adult's airway, which means that smaller objects can cause an airway obstruction in children. Infants and young children generate a less forceful cough than adults, so coughing may not be as effective in relieving an airway obstruction. Finally, children with neuromuscular disorders, developmental delay, traumatic brain injury, and other conditions that affect swallowing are at an increased risk of choking.

In adults, choking often involves food blocking the airway. Risk factors include using alcohol or sedatives, undergoing a procedure involving the oral cavity or pharynx, wearing oral appliances, or having a medical condition that causes difficulty swallowing or impairs the cough reflex. Conditions that can cause difficulty swallowing and/or impaired coughing include neurologic conditions such as strokes, Alzheimer disease, or Parkinson disease. In older adults, risk factors also include living alone, wearing dentures, and having difficulty swallowing.

Children and adults with neurologic, cognitive, or psychiatric disorders may experience a delay in diagnosis because there may not be a known history of a foreign body entering the airway.

The tissues in the mediastinum will slowly resorb the air in the cavity so most pneumomediastinums are treated conservatively. Breathing high flow oxygen will increase the absorption of the air.

If the air is under pressure and compressing the heart, a needle may be inserted into the cavity, releasing the air.

Surgery may be needed to repair the hole in the trachea, esophagus or bowel.

If there is lung collapse, it is imperative the affected individual lies on the side of the collapse, although painful, this allows full inflation of the unaffected lung.

To properly treat a patient with tracheobronchomalacia, the subtype must be determined (primary or secondary). After the type is named, the cause must be identified, whether it is from genetics, a trauma accident, or chronic tracheal illness. If a trauma case or chronic tracheal illnesses were the cause, the first steps of treatment would be to fix or help these underlying issues. If the cause is genetic or the previous underlying issues could not be fixed, other treatments would be assessed. More severe treatments include silicone stenting to prevent tracheal constriction, surgery to strengthen or attempt to rebuild the walls, continuous positive airway pressure that has a machine blow small amounts of air into the trachea to keep it open (mainly at night), or a tracheostomy, which is surgically put into your neck that leads to your trachea to help with breathing. People with tracheobronchomalacia who do not experience symptoms do not need treatment and are often undiagnosed.

Pulmonary diseases may also impact newborns, such as pulmonary hyperplasia, pulmonary interstitial emphysema (usually preterm births), and infant respiratory distress syndrome,

Bronchomalacia is a term for weak cartilage in the walls of the bronchial tubes, often occurring in children under six months. Bronchomalacia means 'floppiness' of some part of the bronchi. Patients present with noisy breathing and/or wheezing. There is collapse of a main stem bronchus on exhalation. If the trachea is also involved the term tracheobronchomalacia (TBM) is used. If only the upper airway the trachea is involved it is called tracheomalacia (TM). There are two types of bronchomalacia. Primary bronchomalacia is due to a deficiency in the cartilaginous rings. Secondary bronchomalacia may occur by extrinsic compression from an enlarged vessel, a vascular ring or a bronchogenic cyst. Though uncommon, idiopathic (of unknown cause) tracheobronchomalacia has been described in older adults.

Bronchomalacia can best be described as a birth defect of the bronchus in the respiratory tract. Congenital malacia of the large airways is one of the few causes of irreversible airways obstruction in children, with symptoms varying from recurrent wheeze and recurrent lower airways infections to severe dyspnea and respiratory insufficiency. It may also be acquired later in life due to chronic or recurring inflammation resulting from infection or other airway disease.

Laryngotracheal stenosis is an umbrella term for a wide and heterogeneous group of very rare conditions. The population incidence of adult post-intubation laryngotracheal stenosis which is the commonest benign sub-type of this condition is approximately 1 in 200,000 adults per year. The main causes of adult laryngotracheal stenosis are:

In one study, peanuts were the most common obstruction. In addition to peanuts, hot dogs, and grapes, latex balloons are also a serious choking hazard in children that can result in death. A latex balloon will conform to the shape of the trachea, blocking the airway and making it difficult to expel with the Heimlich maneuver.

Subcutaneous emphysema is a common result of certain types of surgery; for example it is not unusual in chest surgery. It may also occur from surgery around the esophagus, and is particularly likely in prolonged surgery. Other potential causes are positive pressure ventilation for any reason and by any technique, in which its occurrence is frequently unexpected. It may also occur as a result of oral surgery, laparoscopy, and cricothyrotomy. In a pneumonectomy, in which an entire lung is removed, the remaining bronchial stump may leak air, a rare but very serious condition that leads to progressive subcutaneous emphysema. Air can leak out of the pleural space through an incision made for a thoracotomy to cause subcutaneous emphysema. On infrequent occasions, the condition can result from dental surgery, usually due to use of high-speed tools that are air driven. These cases result in usually painless swelling of the face and neck, with an immediate onset, the crepitus (crunching sound) typical of subcutaneous emphysema, and often with subcutaneous air visible on X-ray.

One of the main causes of subcutaneous emphysema, along with pneumothorax, is an improperly functioning chest tube. Thus subcutaneous emphysema is often a sign that something is wrong with a chest tube; it may be clogged, clamped, or out of place. The tube may need to be replaced, or, when large amounts of air are leaking, a new tube may be added.

Since mechanical ventilation can worsen a pneumothorax, it can force air into the tissues; when subcutaneous emphysema occurs in a ventilated patient, it is an indication that the ventilation may have caused a pneumothorax. It is not unusual for subcutaneous emphysema to result from positive pressure ventilation. Another possible cause is a ruptured trachea. The trachea may be injured by tracheostomy or tracheal intubation; in cases of tracheal injury, large amounts of air can enter the subcutaneous space. An endotracheal tube can puncture the trachea or bronchi and cause subcutaneous emphysema.

Hemoptysis is the coughing up of blood or blood-stained mucus from the bronchi, larynx, trachea, or lungs. This can occur with lung cancer, infections such as tuberculosis, bronchitis, or pneumonia, and certain cardiovascular conditions. Hemoptysis is considered massive at . In such cases, there are always severe injuries. The primary danger comes from choking, rather than blood loss.

Conditions which commonly involve hemoptysis include bronchitis and pneumonia, lung cancers and tuberculosis. Other possible underlying causes include aspergilloma, bronchiectasis, coccidioidomycosis, pulmonary embolism, pneumonic plague, and cystic fibrosis. Rarer causes include hereditary hemorrhagic telangiectasia (HHT or Rendu-Osler-Weber syndrome), Goodpasture's syndrome, and granulomatosis with polyangiitis. In children, hemoptysis is commonly caused by the presence of a foreign body in the airway. The condition can also result from over-anticoagulation from treatment by drugs such as warfarin.

Blood-laced mucus from the sinus or nose area can sometimes be misidentified as symptomatic of hemoptysis (such secretions can be a sign of nasal or sinus cancer, but also a sinus infection). Extensive non-respiratory injury can also cause one to cough up blood. Cardiac causes like congestive heart failure and mitral stenosis should be ruled out.

The origin of blood can be identified by observing its color. Bright-red, foamy blood comes from the respiratory tract, whereas dark-red, coffee-colored blood comes from the gastrointestinal tract. Sometimes hemoptysis may be rust-colored.

The most common cause of minor hemoptysis is bronchitis.

- Lung cancer, including both non-small cell lung carcinoma and small cell lung carcinoma.

- Sarcoidosis

- Aspergilloma

- Tuberculosis

- Histoplasmosis

- Pneumonia

- Pulmonary edema

- Pulmonary embolism

- Foreign body aspiration and aspiration pneumonia

- Goodpasture's syndrome

- Granulomatosis with polyangiitis

- Eosinophilic granulomatosis with polyangiitis (Churg-Strauss syndrome)

- Bronchitis

- Bronchiectasis

- Pulmonary embolism

- Anticoagulant use

- Trauma

- Lung abscess

- Mitral stenosis

- Tropical eosinophilia

- Bleeding disorders

- Hughes-Stovin Syndrome and other variants of Behçet's disease

- Squamous Cell Carcinoma Of Esophagus

Air in subcutaneous tissue does not usually pose a lethal threat; small amounts of air are reabsorbed by the body. Once the pneumothorax or pneumomediastinum that causes the subcutaneous emphysema is resolved, with or without medical intervention, the subcutaneous emphysema will usually clear. However, spontaneous subcutaneous emphysema can, in rare cases, progress to a life-threatening condition, and subcutaneous emphysema due to mechanical ventilation may induce ventilatory failure.

TIF is a rare condition with a .7% frequency, and an mortality rate approaching 100% without surgical intervention. Immediate diagnosis and intervention of an TIF is critical for the surgical intervention success. 25-30% of TIF patients who reach the operating room survive. Recently, the incidence of TIF may have declined due to advances in tracheostomy tube technology and the introduction of the bedside percutaneous dilatational tracheostomy (PDT).

Tracheobronchomalacia or TBM is a condition characterized by flaccidity of the tracheal support cartilage which leads to tracheal collapse. This condition can also affect the bronchi. There are two forms of this rare condition: primary TB and secondary TB. Primary TB is congenital and starts as early as two years old. It is mainly linked to genetic causes. Secondary TB is acquired and starts in adulthood. It is mainly developed after an accident or chronic inflammation.

On 28 May 2013, it was reported that a cure had been developed via a 3D printed windpipe. This cure has currently saved the lives of at least 3 infants.

Rupture of the trachea or bronchus is the most common type of blunt injury to the airway. It is difficult to determine the incidence of TBI: in as many as 30–80% of cases, death occurs before the person reaches a hospital, and these people may not be included in studies. On the other hand, some TBI are so small that they do not cause significant symptoms and are therefore never noticed. In addition, the injury sometimes is not associated with symptoms until complications develop later, further hindering estimation of the true incidence. However, autopsy studies have revealed TBI in 2.5–3.2% of people who died after trauma. Of all neck and chest traumas, including people that died immediately, TBI is estimated to occur in 0.5–2%. An estimated 0.5% of polytrauma patients treated in trauma centers have TBI. The incidence is estimated at 2% in blunt chest and neck trauma and 1–2% in penetrating chest trauma. Laryngotracheal injuries occur in 8% of patients with penetrating injury to the neck, and TBI occurs in 2.8% of blunt chest trauma deaths. In people with blunt trauma who do reach a hospital alive, reports have found incidences of 2.1% and 5.3%. Another study of blunt chest trauma revealed an incidence of only 0.3%, but a mortality rate of 67% (possibly due in part to associated injuries). The incidence of iatrogenic TBI (that caused by medical procedures) is rising, and the risk may be higher for women and the elderly. TBI results about once every 20,000 times someone is intubated through the mouth, but when intubation is performed emergently, the incidence may be as high as 15%.

The mortality rate for people who reach a hospital alive was estimated at 30% in 1966; more recent estimates place this number at 9%. The number of people reaching a hospital alive has increased, perhaps due to improved prehospital care or specialized treatment centers. Of those who reach the hospital alive but then die, most do so within the first two hours of arrival. The sooner a TBI is diagnosed, the higher the mortality rate; this is likely due to other accompanying injuries that prove fatal.

Accompanying injuries often play a key role in the outcome. Injuries that may accompany TBI include pulmonary contusion and laceration; and fractures of the sternum, ribs and clavicles. Spinal cord injury, facial trauma, traumatic aortic rupture, injuries to the abdomen, lung, and head are present in 40–100%. The most common accompanying injury is esophageal perforation or rupture (known as Boerhaave syndrome), which occurs in as many as 43% of the penetrating injuries to the neck that cause tracheal injury.

If the person is awake and able to breathe often all that is requires is providing extra oxygen while the operating room is prepared for bronchoscopy.

If a children less than one and is unable to breathe at all then five back blows followed by five chest thrusts should be done. In children over the age of one abdominal thrusts are recommended.

If this is not effective than bag mask ventilation is recommended. Next laryngoscopy can be tried to look and see if the foreign body can be removed. If the above is not effective than intubation or cricothyrotomy can be tried.