The cause of IPF is unknown but certain environmental factors and exposures have been shown to increase the risk of getting IPF. Cigarette smoking is the best recognized and most accepted risk factor for IPF, and increases the risk of IPF by about twofold. Other environmental and occupation exposures such as exposure to metal dust, wood dust, coal dust, silica, stone dust, biologic dusts coming from hay dust or mold spores or other agricultural products, and occupations related to farming/livestock have also been shown to increase the risk for IPF. There is some evidence that viral infections may be associated with idiopathic pulmonary fibrosis and other fibrotic lung diseases.

The clinical course of IPF can be unpredictable. IPF progression is associated with an estimated median survival time of 2 to 5 years following diagnosis.

The 5-year survival for IPF ranges between 20–40%, a mortality rate higher than that of a number of malignancies, including colon cancer, multiple myeloma and bladder cancer.

Recently a multidimensional index and staging system has been proposed to predict mortality in IPF. The name of the index is GAP and is based on gender [G], age [A], and two lung physiology variables [P] (FVC and DL that are commonly measured in clinical practice to predict mortality in IPF. The highest stage of GAP (stage III) has been found to be associated with a 39% risk of mortality at 1 year. This model has also been evaluated in IPF and other ILDs and shown good performance in predicting mortality in all main ILD subtypes. A modified ILD-GAP Index has been developed for application across ILD subtypes to provide disease-specific survival estimates. In IPF patients, the overall mortality at 5 years rate is high but the annual rate of all-cause mortality in patients with mild to moderate lung impairment is relatively low. This is the reason why change in lung function (FVC) is usually measured in 1-year clinical trials of IPF treatments rather than survival.

In addition to clinical and physiological parameters to predict how rapidly patients with IPF might progress, genetic and molecular features are also associated with IPF mortality. For example, it has been shown that IPF patients who have a specific genotype in the mucin MUC5B gene polymorphism (see above) experience slower decline in FVC and significantly improved survival. Even if such data are interesting from a scientific point of view, the application in the clinical routine of a prognostic model based on specific genotypes is still not possible.

Pulmonary fibrosis may be a secondary effect of other diseases. Most of these are classified as interstitial lung diseases. Examples include autoimmune disorders, viral infections and bacterial infection like tuberculosis which may cause fibrotic changes in both lungs upper or lower lobes and other microscopic injuries to the lung. However, pulmonary fibrosis can also appear without any known cause. In this case, it is termed "idiopathic". Most idiopathic cases are diagnosed as "idiopathic pulmonary fibrosis". This is a diagnosis of exclusion of a characteristic set of histologic/pathologic features known as usual interstitial pneumonia (UIP). In either case, there is a growing body of evidence which points to a genetic predisposition in a subset of patients. For example, a mutation in surfactant protein C (SP-C) has been found to exist in some families with a history of pulmonary fibrosis.

Diseases and conditions that may cause pulmonary fibrosis as a secondary effect include:

- Inhalation of environmental and occupational pollutants, such as metals in asbestosis, silicosis and exposure to certain gases. Coal miners, ship workers and sand blasters among others are at higher risk.

- Hypersensitivity pneumonitis, most often resulting from inhaling dust contaminated with bacterial, fungal, or animal products.

- Cigarette smoking can increase the risk or make the illness worse.

- Some typical connective tissue diseases such as rheumatoid arthritis, SLE and scleroderma

- Other diseases that involve connective tissue, such as sarcoidosis and granulomatosis with polyangiitis.

- Infections

- Certain medications, e.g. amiodarone, bleomycin (pingyangmycin), busulfan, methotrexate, apomorphine, and nitrofurantoin

- Radiation therapy to the chest

PAM is one of the rare lung diseases currently being studied by the Rare Lung Diseases Consortium (RLDC). Pulmonary Alveolar Microlithiasis patients, families, and caregivers are encouraged to join the NIH Rare Lung Diseases Consortium Contact Registry. This is a privacy protected site that provides up-to-date information for individuals interested in the latest scientific news, trials, and treatments related to rare lung diseases.

Five million people worldwide are affected by pulmonary fibrosis. A wide range of incidence and prevalence rates have been reported for pulmonary fibrosis. The rates below are per 100,000 persons, and the ranges reflect narrow and broad inclusion criteria, respectively.

Based on these rates, pulmonary fibrosis prevalence in the United States could range from more than 29,000 to almost 132,000, based on the population in 2000 that was 18 years or older. The actual numbers may be significantly higher due to misdiagnosis. Typically, patients are in their forties and fifties when diagnosed while the incidence of idiopathic pulmonary fibrosis increases dramatically after the age of fifty. However, loss of pulmonary function is commonly ascribed to old age, heart disease or to more common lung diseases.

According to a recent study, the main risk factors for RA-ILD are advancing age, male sex, greater RA disease activity, rheumatoid factor (RF) positivity, and elevated titers of anticitrullinated protein antibodies such as anticyclic citrullinated peptide. Cigarette smoking also appears to increase risk of RA-ILD, especially in patients with human leukocyte antigen DRB1.

A recently published retrospective study by a team from Beijing Chao-Yang Hospital in Beijing, China, supported three of the risk factors listed for RA-ILD and identified an additional risk factor. In that study of 550 RA patients, logistic regression analysis of data collected on the 237 (43%) with ILD revealed that age, smoking, RF positivity, and elevated lactate dehydrogenase closely correlated with ILD.

Recent studies have identified risk factors for disease progression and mortality. A retrospective study of 167 patients with RA-ILD determined that the usual interstitial pneumonia (UIP) pattern on high-resolution computed tomography (HRCT) was a risk factor for progression, as were severe disease upon diagnosis and rate of change in pulmonary function test results in the first 6 months after diagnosis.

A study of 59 RA-ILD patients found no median survival difference between those with the UIP pattern and those without it. But the UIP group had more deaths, hospital admissions, need for supplemental oxygen, and decline in lung function.

ILD may be classified according to the cause. One method of classification is as follows:

1. Inhaled substances

- Inorganic

- Silicosis

- Asbestosis

- Berylliosis

- printing workers (eg. carbon bblack, ink mist)

- Organic

- Hypersensitivity pneumonitis

2. Drug-induced

- Antibiotics

- Chemotherapeutic drugs

- Antiarrhythmic agents

3. Connective tissue and Autoimmune diseases

- Rheumatoid arthritis

- Systemic lupus erythematosus

- Systemic sclerosis

- Polymyositis

- Dermatomyositis

4. Infection

- Atypical pneumonia

- Pneumocystis pneumonia (PCP)

- Tuberculosis

- "Chlamydia" trachomatis

- Respiratory Syncytial Virus

5. Idiopathic

- Sarcoidosis

- Idiopathic pulmonary fibrosis

- Hamman-Rich syndrome

- Antisynthetase syndrome

6. Malignancy

- Lymphangitic carcinomatosis

7. Predominantly in children

- Diffuse developmental disorders

- Growth abnormalities deficient alveolarisation

- Infant conditions of undefined cause

- ILD related to alveolar surfactant region

PAP patients, families, and caregivers are encouraged to join the NIH Rare Lung Diseases Consortium Contact Registry. This is a privacy protected site that provides up-to-date information for individuals interested in the latest scientific news, trials, and treatments related to rare lung diseases.

Interstitial lung disease (ILD), or diffuse parenchymal lung disease (DPLD), is a group of lung diseases affecting the interstitium (the tissue and space around the air sacs of the lungs). It concerns alveolar epithelium, pulmonary capillary endothelium, basement membrane, perivascular and perilymphatic tissues. It may occur when an injury to the lungs triggers an abnormal healing response. Ordinarily, the body generates just the right amount of tissue to repair damage. But in interstitial lung disease, the repair process goes awry and the tissue around the air sacs (alveoli) becomes scarred and thickened. This makes it more difficult for oxygen to pass into the bloodstream. The term ILD is used to distinguish these diseases from obstructive airways diseases.

In children, several unique forms of ILD exist which are specific for the young age groups. The acronym chILD is used for this group of diseases and is derived from the English name, Children’s Interstitial Lung Diseases – chILD.

Prolonged ILD may result in pulmonary fibrosis, but this is not always the case. Idiopathic pulmonary fibrosis is interstitial lung disease for which no obvious cause can be identified (idiopathic), and is associated with typical findings both radiographic (basal and pleural based fibrosis with honeycombing) and pathologic (temporally and spatially heterogeneous fibrosis, histopathologic honeycombing and fibroblastic foci).

In 2013 interstitial lung disease affected 595,000 people globally. This resulted in 471,000 deaths.

The disease is more common in males and in tobacco smokers.

In a recent epidemiologic study from Japan, Autoimmune PAP has an incidence and prevalence higher than previously reported and is not strongly linked to smoking, occupational exposure, or other illnesses.

Endogenous lipoid pneumonia and non-specific interstitial pneumonitis has been seen prior to the development of PAP in a child.

Patients, families, and caregivers are encouraged to join the NIH Rare Lung Diseases Consortium Contact Registry. This is a privacy protected site that provides up-to-date information for individuals interested in the latest scientific news, trials, and treatments related to rare lung diseases.

The most common cause is post-surgical atelectasis, characterized by splinting, i.e. restricted breathing after abdominal surgery.

Another common cause is pulmonary tuberculosis. Smokers and the elderly are also at an increased risk. Outside of this context, atelectasis implies some blockage of a bronchiole or bronchus, which can be within the airway (foreign body, mucus plug), from the wall (tumor, usually squamous cell carcinoma) or compressing from the outside (tumor, lymph node, tubercle). Another cause is poor surfactant spreading during inspiration, causing the surface tension to be at its highest which tends to collapse smaller alveoli. Atelectasis may also occur during suction, as along with sputum, air is withdrawn from the lungs. There are several types of atelectasis according to their underlying mechanisms or the distribution of alveolar collapse; resorption, compression, microatelectasis and contraction atelectasis.

The rate of BPD varies among institutions, which may reflect neonatal risk factors, care practices (e.g., target levels for acceptable oxygen saturation), and differences in the clinical definitions of BPD.

Since the disease was first described in 1918, over 500 case reports have appeared in the literature. PAM is associated with consanguinity. The incidence is higher in Turkey, Japan, India and Italy. The mean age at diagnosis is 35 years based on the cases reported in the literature.

The exact cause of rheumatoid lung disease is unknown. However, associated factors could be due largely to smoking. Sometimes, the medicines used to treat rheumatoid arthritis, especially methotrexate, may result in lung disease.

Prevention's:

- Stop smoking: Chemicals found in cigarettes can irritate already delicate lung tissue, leading to further complications.

- Having regular checkups: The doctor could listen to lungs and monitor breathing, because lung problems that are detected early can be easier to treat.

The annual incidence of ARDS is 13–23 people per 100,000 in the general population. Its incidence in the mechanically ventilated population in intensive care units is much higher. According to Brun-Buisson "et al" (2004), there is a prevalence of acute lung injury (ALI) of 16.1% percent in ventilated patients admitted for more than 4 hours.

Worldwide, severe sepsis is the most common trigger causing ARDS. Other triggers include mechanical ventilation, sepsis, pneumonia, Gilchrist's disease, drowning, circulatory shock, aspiration, traumaespecially pulmonary contusionmajor surgery, massive blood transfusions, smoke inhalation, drug reaction or overdose, fat emboli and reperfusion pulmonary edema after lung transplantation or pulmonary embolectomy. Pneumonia and sepsis are the most common triggers, and pneumonia is present in up to 60% of patients and may be either causes or complications of ARDS. Alcohol excess appears to increase the risk of ARDS. Diabetes was originally thought to decrease the risk of ARDS, but this has shown to be due to an increase in the risk of pulmonary edema. Elevated abdominal pressure of any cause is also probably a risk factor for the development of ARDS, particularly during mechanical ventilation.

The death rate varies from 25–40% in centers using up-to-date ventilatory strategies and up to 58% in all centers.

To date, about 420 cases have been reported in the medical literature. Given its unusual nature, the true prevalence of PB is unknown, and it is likely that many patients are undiagnosed. PB does affect patients of all age groups and both genders.

The atmosphere is composed of 78% nitrogen and 21% oxygen. Since oxygen is exchanged at the alveoli-capillary membrane, nitrogen is a major component for the alveoli's state of inflation. If a large volume of nitrogen in the lungs is replaced with oxygen, the oxygen may subsequently be absorbed into the blood, reducing the volume of the alveoli, resulting in a form of alveolar collapse known as absorption atelectasis.

Pulmonary venoocclusive disease is rare, difficult to diagnose, and probably frequently misdiagnosed as idiopathic pulmonary arterial hypertension. Prevalence in parts of Europe is estimated to be 0.1-0.2 cases per million.

PVOD appears to occur as frequently in men as in women, and age at diagnosis ranges from 7–74 years with a median of 39 years. PVOD may occur in patients with associated diseases such as HIV, bone marrow transplantation, and connective tissue diseases. PVOD has also been associated with several chemotherapy regimens such as bleomycin, BCNU, and mitomycin.

Injury to the lung may also cause pulmonary edema through injury to the vasculature and parenchyma of the lung. The acute lung injury-acute respiratory distress syndrome (ALI-ARDS) covers many of these causes, but they may include:

- Inhalation of hot or toxic gases

- Pulmonary contusion, i.e., high-energy trauma (e.g. vehicle accidents)

- Aspiration, e.g., gastric fluid

- Reexpansion, i.e. post large volume thoracocentesis, resolution of pneumothorax, post decortication, removal of endobronchial obstruction, effectively a form of negative pressure pulmonary oedema.

- Reperfusion injury, i.e. postpulmonary thromboendartectomy or lung transplantation

- Swimming induced pulmonary edema also known as immersion pulmonary edema

- Transfusion Associated Circulatory Overload (TACO) occurs when multiple blood transfusions or blood-products (plasma, platelets, etc.) are transfused over a short period of time.

- Transfusion associated Acute Lung Injury (TRALI) is a specific type of blood-product transfusion injury that occurs when the donors plasma contained antibodies against the donor, such as anti-HLA or anti-neutrophil antibodies.

- Severe infection or inflammation which may be local or systemic. This is the classical form of ALI-ARDS.

Some causes of pulmonary edema are less well characterised and arguably represent specific instances of the broader classifications above.

- Arteriovenous malformation

- Hantavirus pulmonary syndrome

- High altitude pulmonary edema (HAPE)

- Envenomation, such as with the venom of Atrax robustus

Since ARDS is an extremely serious condition which requires invasive forms of therapy it is not without risk. Complications to be considered include the following:

- Pulmonary: barotrauma (volutrauma), pulmonary embolism (PE), pulmonary fibrosis, ventilator-associated pneumonia (VAP)

- Gastrointestinal: bleeding (ulcer), dysmotility, pneumoperitoneum, bacterial translocation

- Cardiac: abnormal heart rhythms, myocardial dysfunction

- Kidney: acute kidney failure, positive fluid balance

- Mechanical: vascular injury, pneumothorax (by placing pulmonary artery catheter), tracheal injury/stenosis (result of intubation and/or irritation by endotracheal tube

- Nutritional: malnutrition (catabolic state), electrolyte deficiency.

Clinically, the most serious and immediate complication is acute respiratory distress syndrome (ARDS), which usually occurs within 24 h. Those with significant lower airway involvement may develop bacterial infection. Importantly, victims suffering body surface burn and smoke inhalation are the most susceptible. Thermal injury combined with inhalation injury compromises pulmonary function, producing microvascular hyperpermeability that leads to a significant increase in lung lymph flow and pulmonary edema. The terrorist attack on the World Trade Center on September 11, 2001 left many people with impaired lung function. A study of firefighters and EMS workers enrolled in the FDNY WTC Medical Monitoring and Treatment Program, whose lung function was tested prior to 9/11, documented a steep decline in lung function in the first year after 9/11. A new study that includes a thousand additional workers shows that the declines have persisted over time. Prior to 9/11, 3% of firefighters had below-normal lung function, one year after 9/11 nearly 19% did, and six years later it stabilized at 13%. Ten to 14 days after acute exposure to some agents (e.g. ammonia, nitrogen oxides, sulfur dioxide, mercury), some patients develop bronchiolitis obliterans progressing to ARDS. Bronchiolitis obliterans with organized pneumonia can ensue when granulation tissue accumulates in the terminal airways and alveolar ducts during the body's reparative process. A minority of these patients develop late pulmonary fibrosis. Also at enhanced risk are persons with co-morbidities. Several studies report that both aged persons and smokers are especially vulnerable to the adverse effects of inhalation injury.

The genetic cause of pulmonary veno-occlusive disease is mutations in EIF2AK4 gene. Though this does not mean other possible causes do not exist, such as viral infection and risk of toxic chemicals (chemotherapy drugs).

The prognosis of pulmonary arterial hypertension (WHO Group I) has an "untreated" median survival of 2–3 years from time of diagnosis, with the cause of death usually being right ventricular failure (cor pulmonale). A recent outcome study of those patients who had started treatment with bosentan (Tracleer) showed that 89% patients were alive at 2 years. With new therapies, survival rates are increasing. For 2,635 patients enrolled in The Registry to Evaluate Early and Long-term Pulmonary Arterial Hypertension Disease Management (REVEAL Registry) from March 2006 to December 2009, 1-, 3-, 5-, and 7-year survival rates were 85%, 68%, 57%, and 49%, respectively. For patients with idiopathic/familial PAH, survival rates were 91%, 74%, 65%, and 59%. Levels of mortality are very high in pregnant women with severe pulmonary arterial hypertension (WHO Group I). Pregnancy is sometimes described as contraindicated in these women.

"Flash pulmonary edema" ("FPE"), is rapid onset pulmonary edema. It is most often precipitated by acute myocardial infarction or mitral regurgitation, but can be caused by aortic regurgitation, heart failure, or almost any cause of elevated left ventricular filling pressures. Treatment of FPE should be directed at the underlying cause, but the mainstays are ensuring adequate oxygenation, diuresis, and decrease of pulmonary circulation pressures.

Recurrence of FPE is thought to be associated with hypertension and may signify renal artery stenosis. Prevention of recurrence is based on managing hypertension, coronary artery disease, renovascular hypertension, and heart failure.