The primary risk factor for COPD globally is tobacco smoking. Of those who smoke, about 20% will get COPD, and of those who are lifelong smokers, about half will get COPD. In the United States and United Kingdom, of those with COPD, 80–95% are either current smokers or previously smoked. The likelihood of developing COPD increases with the total smoke exposure. Additionally, women are more susceptible to the harmful effects of smoke than men. In nonsmokers, secondhand smoke is the cause of about 20% of cases. Other types of smoke, such as, marijuana, cigar, and water-pipe smoke, also confer a risk. Water-pipe smoke appears to be as harmful as smoking cigarettes. Problems from marijuana smoke may only be with heavy use. Women who smoke during pregnancy may increase the risk of COPD in their child. For the same amount of cigarette smoking, women have a higher risk of COPD than men.

Poorly ventilated cooking fires, often fueled by coal or biomass fuels such as wood and dung, lead to indoor air pollution and are one of the most common causes of COPD in developing countries. These fires are a method of cooking and heating for nearly 3 billion people, with their health effects being greater among women due to more exposure. They are used as the main source of energy in 80% of homes in India, China and sub-Saharan Africa.

People who live in large cities have a higher rate of COPD compared to people who live in rural areas. While urban air pollution is a contributing factor in exacerbations, its overall role as a cause of COPD is unclear. Areas with poor outdoor air quality, including that from exhaust gas, generally have higher rates of COPD. The overall effect in relation to smoking, however, is believed to be small.

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.

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.

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

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

Health care professionals are at risk of occupational influenza exposure; during a pandemic influenza, anyone in a close environment is at risk, including those in an office environment.

Asthma is a respiratory disease that can begin or worsen due to exposure at work and is characterized by episodic narrowing of the respiratory tract. Occupational asthma has a variety of causes, including sensitization to a specific substance, causing an allergic response; or a reaction to an irritant that is inhaled in the workplace. Exposure to various substances can also worsen pre-existing asthma. People who work in isocyanate manufacturing, who use latex gloves, or who work in an indoor office environment are at higher risk for occupational asthma than the average US worker. Approximately 2 million people in the US have occupational asthma.

Aspergillosis is an infection caused by the fungus "Aspergillus". Aspergillosis describes a large number of diseases involving both infection and growth of fungus as well as allergic responses. Aspergillosis can occur in a variety of organs, both in humans and animals.

The most common sites of infection are the respiratory apparatus (lungs, sinuses) and these infections can be:

- Invasive (e.g. – IPA)

- Non-invasive (e.g. Allergic Pulmonary Aspergillosis - ABPA)

- Chronic pulmonary and aspergilloma (e.g. chronic cavitary, semi-invasive)

- Severe asthma with fungal sensitisation (SAFS)

Chronic pulmonary aspergillosis (CPA) is a long-term aspergillus infection of the lung and "Aspergillus fumigatus" is almost always the species responsible for this illness. Patients fall into several groups as listed below.

- Those with an aspergilloma which is a ball of fungus found in a single lung cavity - which may improve or disappear, or change very little over a few years.

- Aspergillus nodule

- Chronic cavitary pulmonary aspergillosis (CCPA) where cavities are present in the lungs, but not necessarily with a fungal ball (aspergilloma).

- Chronic fibrosing pulmonary aspergillosis this may develop where pulmonary aspergillosis remains untreated and chronic scarring of the lungs occurs. Unfortunately scarring of the lungs does not improve.

Most patients with CPA have or have had an underlying lung disease. The most common diseases include tuberculosis, atypical mycobacterium infection, stage III fibrocystic pulmonary sarcoidosis, ABPA, lung cancer, COPD and emphysema, asthma and silicosis.

Pneumonia is due to infections caused primarily by bacteria or viruses and less commonly by fungi and parasites. Although there are more than 100 strains of infectious agents identified, only a few are responsible for the majority of the cases. Mixed infections with both viruses and bacteria may occur in up to 45% of infections in children and 15% of infections in adults. A causative agent may not be isolated in approximately half of cases despite careful testing.

The term "pneumonia" is sometimes more broadly applied to any condition resulting in inflammation of the lungs (caused for example by autoimmune diseases, chemical burns or drug reactions); however, this inflammation is more accurately referred to as pneumonitis.

Conditions and risk factors that predispose to pneumonia include smoking, immunodeficiency, alcoholism, chronic obstructive pulmonary disease, asthma, chronic kidney disease, and liver disease. The use of acid-suppressing medications—such as proton-pump inhibitors or H2 blockers—is associated with an increased risk of pneumonia. The risk is also increased in old age.

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

It is not practical to test or decontaminate most sites that may be contaminated with "H. capsulatum", but the following sources list environments where histoplasmosis is common, and precautions to reduce a person's risk of exposure, in the three parts of the world where the disease is prevalent. Precautions common to all geographical locations would be to avoid accumulations of bird or bat droppings.

The US National Institute for Occupational Safety and Health (NIOSH) provides information on work practices and personal protective equipment that may reduce the risk of infection. This document is available in English and Spanish.

Authors at the University of Nigeria have published a review which includes information on locations in which histoplasmosis has been found in Africa (in chicken runs, bats and the caves bats infest, and in soil), and a thorough reference list including English, French, and Spanish language references.

There are several populations that have a higher risk for contracting coccidioidomycosis and developing the advanced disseminated version of the disease. Populations with exposure to the airborne arthroconidia working in agriculture and construction have a higher risk. Outbreaks have also been linked to earthquakes, windstorms and military training exercises where the ground is disturbed. Historically an infection is more likely to occur in males than females, although this could be attributed to occupation rather than gender specific. Women who are pregnant and immediately postpartum are at a high risk of infection and dissemination. There is also an association between stage of pregnancy and severity of the disease, with third trimester women being more likely to develop dissemination. Presumably this is related to highly elevated hormonal levels, which stimulate growth and maturation of spherules and subsequent release of endospores. Certain ethnic populations are more susceptible to disseminated coccioidomycosis. The risk of dissemination is 175 times greater in Filipinos and 10 times greater in African Americans than non-Hispanic whites. Individuals with a weakened immune system are also more susceptible to the disease. In particular, individuals with HIV and diseases that impair T-cell function. Individuals with pre-existing conditions such as diabetes are also at a higher risk. Age also affects the severity of the disease, with more than one third of deaths being in the 65-84 age group.

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.

Bacteria are the most common cause of community-acquired pneumonia (CAP), with "Streptococcus pneumoniae" isolated in nearly 50% of cases. Other commonly isolated bacteria include "Haemophilus influenzae" in 20%, "Chlamydophila pneumoniae" in 13%, and "Mycoplasma pneumoniae" in 3% of cases; "Staphylococcus aureus"; "Moraxella catarrhalis"; "Legionella pneumophila" and Gram-negative bacilli. A number of drug-resistant versions of the above infections are becoming more common, including drug-resistant "Streptococcus pneumoniae" (DRSP) and methicillin-resistant Staphylococcus aureus (MRSA).

The spreading of organisms is facilitated when risk factors are present. Alcoholism is associated with "Streptococcus pneumoniae", anaerobic organisms, and "Mycobacterium tuberculosis"; smoking facilitates the effects of "Streptococcus pneumoniae", "Haemophilus influenzae", "Moraxella catarrhalis", and "Legionella pneumophila". Exposure to birds is associated with "Chlamydia psittaci"; farm animals with "Coxiella burnetti"; aspiration of stomach contents with anaerobic organisms; and cystic fibrosis with "Pseudomonas aeruginosa" and "Staphylococcus aureus". "Streptococcus pneumoniae" is more common in the winter, and should be suspected in persons aspirating a large amount of anaerobic organisms.

Alveolar lung diseases, are a group of diseases that mainly affect the alveoli of the lungs.

Unfortunately for non-healthcare professionals, healthcare professionals can use many different words for pulmonary toxicity and still understand each other completely. Yet, for laypersons, this can lead to some difficulties while searching for information about pulmonary toxicity (or about any other side effect). Here are some words that are rather similar to each other in meaning for healthcare professionals. Side effect = adverse event (AE) = adverse drug reaction (ADR) = adverse reaction = toxicity. Pulmonary = lung. Pulmonary toxicity = pulmonary injury = lung injury = lung toxicity. And instead of pulmonary toxicity (a general term), the specific name of the specific side effect in question can be used, e.g. pneumonitis or radiation pneumonitis. Any combination is also possible, of course.

Equine multinodular pulmonary fibrosis is a chronic lung disease of horses. There is evidence that the disease is caused by infection with a gammaherpesvirus, equine herpesvirus 5. The disease affects adult (usually older) horses, causing weight loss and reduced ability to exercise as a result of the formation of nodular lesions in the lungs.

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.

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

Acute bronchitis is one of the most common diseases. About 5% of adults are affected and about 6% of children have at least one episode a year. It occurs more often in the winter. More than 10 million people in the United States visit a doctor each year for this condition with about 70% receiving antibiotics which are mostly not needed. There are efforts to decrease the use of antibiotics in acute bronchitis.

Patients with single aspergillomas generally do well with surgery to remove the aspergilloma, and are best given pre-and post-operative antifungal drugs. Often, no treatment is necessary. However, if a patient coughs up blood (haemoptysis), treatment may be required (usually angiography and embolisation, surgery or taking tranexamic acid). Angiography (injection of dye into the blood vessels) may be used to find the site of bleeding which may be stopped by shooting tiny pellets into the bleeding vessel.

For chronic cavitary pulmonary aspergillosis and chronic fibrosing pulmonary aspergillosis, lifelong use of antifungal drugs is usual. Itraconazole and voriconazole are first and second-line anti fungal agents respectively. Posaconazole can be used as third-line agent, for patients who are intolerant of or developed resistance to the first and second-line agents. Regular chest X-rays, serological and mycological parameters as well as quality of life questionnaires are used to monitor treatment progress. It is important to monitor the blood levels of antifungals to ensure optimal dosing as individuals vary in their absorption levels of these drugs.

Alveolar lung disease may be divided into acute or chronic. Causes of acute alveolar lung disease include pulmonary edema (cardiogenic or neurogenic), pneumonia (bacterial or viral), pulmonary embolism, systemic lupus erythematosus, bleeding in the lungs (e.g., Goodpasture syndrome), idiopathic pulmonary hemosiderosis, and granulomatosis with polyangiitis.

Chronic alveolar lung disease can be caused by pulmonary alveolar proteinosis, alveolar cell carcinoma, mineral oil pneumonia, sarcoidosis (alveolar form), lymphoma, tuberculosis, metastases, or desquamative interstitial pneumonia.

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.

Preventing Valley fever is challenging because it is difficult to avoid breathing in the fungus should it be present, however, the public health effect of the disease is essential to understand in areas where the fungus is endemic. Enhancing surveillance of Coccidiodomycosis is key to preparedness in the medical field in addition to improving diagnostics for early infections. Currently there are no completely effective preventive measures available for people who live or travel through Valley Fever -endemic areas. Recommended preventive measures include avoiding airborne dust or dirt, but this does not guarantee protection against infection. People in certain occupations may be advised to wear face masks. The use of air filtration indoors is also helpful, in addition to keeping skin injuries clean and covered to avoid skin infection.

In 1998-2011, there were 111,117 cases of coccidioidomycosis in the U.S. that were logged into the National Notifiable Diseases Surveillance System (NNDSS). Since many U.S. states do not require reporting of coccidioidomycosis, the actual numbers can be higher. The United States' Centers for Disease Control and Prevention (CDC) called the disease a "silent epidemic" and acknowledged that there is no proven anticoccidioidal vaccine available. Studies done in the past show that the cost benefit of a vaccine is most notable among infants, teens, and immigrant adults, with negative cost-benefit results among older age groups.

Raising both surveillance and awareness of the disease while medical researchers are developing a human vaccine can positively contribute towards prevention efforts. Research demonstrates that patients from endemic areas who are aware of the disease are most likely to request diagnostic testing for coccidioidomycosis. Presently, Meridian Bioscience manufactures the so-called "EIA test" to diagnose the Valley fever, which however is known for producing a fair quantity of false positives. Currently, recommended prevention measures can include type-of-exposure-based respirator protection for persons engaged in agriculture, construction and others working outdoors in endemic areas. Dust control measures such as planting grass and wetting the soil, and also limiting exposure to dust storms are advisable for residential areas in endemic regions.