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.

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.

As the lungs tend to be vulnerable organs due to their exposure to harmful particles in the air, several things can cause an acute exacerbation of COPD:

- Respiratory infection, being responsible for approximately half of COPD exacerbations. Approximately half of these are due to viral infections and another half appears to be caused by bacterial infections. Common bacterial pathogens of acute exacerbations include "Haemophilus influenzae", "Streptococcus pneumoniae" and "Moraxella catarrhalis". Less common bacterial pathogens include "Chlamydia pneumoniae" and "MRSA". Pathogens seen more frequently in patients with impaired lung function (FEV<35% of predicted) include "Haemophilus parainfluenzae" (after repeated use of antibiotics), "Mycoplasma pneumoniae" and gram-negative, opportunistic pathogens like "Pseudomonas aeruginosa" and "Klebsiella pneumoniae".

- Allergens, e.g., pollens, wood or cigarette smoke, pollution

- Toxins, including a variety of different chemicals

- Air pollution

- Failing to follow a drug therapy program, e.g. improper use of an inhaler

In one-third of all COPD exacerbation cases, the cause cannot be identified.

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.

Acute exacerbations can be partially prevented. Some infections can be prevented by vaccination against pathogens such as influenza and "Streptococcus pneumoniae". Regular medication use can prevent some COPD exacerbations; long acting beta-adrenoceptor agonists (LABAs), long-acting anticholinergics, inhaled corticosteroids and low-dose theophylline have all been shown to reduce the frequency of COPD exacerbations. Other methods of prevention include:

- Smoking cessation and avoiding dust, passive smoking, and other inhaled irritants

- Yearly influenza and 5-year pneumococcal vaccinations

- Regular exercise, appropriate rest, and healthy nutrition

- Avoiding people currently infected with e.g. cold and influenza

- Maintaining good fluid intake and humidifying the home, in order to help reduce the formation of thick sputum and chest congestion.

Most cases of chronic bronchitis are caused by smoking cigarettes or other forms of tobacco. Additionally, chronic inhalation of air pollution or irritating fumes or dust from hazardous exposures in occupations such as coal mining, grain handling, textile manufacturing, livestock farming, and metal moulding may also be a risk factor for the development of chronic bronchitis. Protracted bacterial bronchitis is usually caused by "Streptococcus pneumoniae", "Non-typable Haemophilus influenzae", or "Moraxella catarrhalis".

Status asthmaticus is slightly more common in males and is more common among people of African and Hispanic origin. The gene locus glutathione dependent S-nitrosoglutathione (GSNOR) has been suggested as one possible correlation to development of status asthmaticus.

The hygiene hypothesis attempts to explain the increased rates of asthma worldwide as a direct and unintended result of reduced exposure, during childhood, to non-pathogenic bacteria and viruses. It has been proposed that the reduced exposure to bacteria and viruses is due, in part, to increased cleanliness and decreased family size in modern societies. Exposure to bacterial endotoxin in early childhood may prevent the development of asthma, but exposure at an older age may provoke bronchoconstriction. Evidence supporting the hygiene hypothesis includes lower rates of asthma on farms and in households with pets.

Use of antibiotics in early life has been linked to the development of asthma. Also, delivery via caesarean section is associated with an increased risk (estimated at 20–80%) of asthma—this increased risk is attributed to the lack of healthy bacterial colonization that the newborn would have acquired from passage through the birth canal. There is a link between asthma and the degree of affluence which may be related to the hygiene hypothesis as less affluent individuals often have more exposure to bacteria and viruses.

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.

Many environmental factors have been associated with asthma's development and exacerbation including allergens, air pollution, and other environmental chemicals. Smoking during pregnancy and after delivery is associated with a greater risk of asthma-like symptoms. Low air quality from factors such as traffic pollution or high ozone levels has been associated with both asthma development and increased asthma severity. Over half of cases in children in the United States occur in areas with air quality below EPA standards. Low air quality is more common in low-income and minority communities.

Exposure to indoor volatile organic compounds may be a trigger for asthma; formaldehyde exposure, for example, has a positive association. Also, phthalates in certain types of PVC are associated with asthma in children and adults. While exposure to pesticides is linked to the development of asthma it is unclear if this is a cause and effect relationship.

There is an association between acetaminophen (paracetamol) use and asthma. The majority of the evidence does not, however, support a causal role. A 2014 review found that the association disappeared when respiratory infections were taken into account. Use by a mother during pregnancy is also associated with an increased risk as is psychological stress during pregnancy.

Asthma is associated with exposure to indoor allergens. Common indoor allergens include dust mites, cockroaches, animal dander (fragments of fur or feathers), and mold. Efforts to decrease dust mites have been found to be ineffective on symptoms in sensitized subjects. Certain viral respiratory infections, such as respiratory syncytial virus and rhinovirus, may increase the risk of developing asthma when acquired as young children. Certain other infections, however, may decrease the risk.

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.

Tobacco smoke is a known carcinogen. Workers in the hospitality industry may be exposed to tobacco smoke in the workplace, especially in environments like casinos and bars/restaurants.

Tuberculosis, pneumonia, inhaled foreign bodies, allergic bronchopulmonary aspergillosis and bronchial tumours are the major acquired causes of bronchiectasis. Infective causes associated with bronchiectasis include infections caused by the Staphylococcus, Klebsiella, or Bordetella pertussis, the causative agent of whooping cough and nontuberculous mycobacteria.

Aspiration of ammonia and other toxic gases, pulmonary aspiration, alcoholism, heroin (drug use), various allergies all appear to be linked to the development of bronchiectasis.

Various immunological and lifestyle factors have also been linked to the development of bronchiectasis:

- Childhood Acquired Immune Deficiency Syndrome (AIDS), which predisposes patients to a variety of pulmonary ailments, such as pneumonia and other opportunistic infections.

- Inflammatory bowel disease, especially ulcerative colitis. It can occur in Crohn's disease as well, but does so less frequently. Bronchiectasis in this situation usually stems from various allergic responses to inhaled fungal spores. A Hiatal hernia can cause Bronchiectasis when the stomach acid that is aspirated into the lungs causes tissue damage.

- People with rheumatoid arthritis who smoke appear to have a tenfold increased rate of the disease. Still, it is unclear as to whether or not cigarette smoke is a specific primary cause of bronchiectasis.

- Case reports of Hashimoto's thyroiditis and bronchiectasis occurring in the same persons have been published.

No cause is identified in up to 50% of non-cystic-fibrosis related bronchiectasis.

Reactive airways dysfunction syndrome (RADS) is a term proposed by Stuart M. Brooks and colleagues in 1985

It can also manifest in adults with exposure to high levels of chlorine, ammonia, acetic acid or sulphur dioxide, creating symptoms like asthma. These symptoms can vary from mild to fatal, and can even create long-term airway damage depending on the amount of exposure and the concentration of chlorine. Some experts classify RADS as occupational asthma. Those with exposure to highly irritating substances should receive treatment to mitigate harmful effects.

There are limited national and international studies into the burden of ABPA, made more difficult by a non-standardized diagnostic criteria. Estimates of between 0.5–3.5% have been made for ABPA burden in asthma, and 1–17.7% in CF. Five national cohorts, detecting ABPA prevalence in asthma (based on GINA estimates), were used in a recent meta-analysis to produce an estimate of the global burden of ABPA complicating asthma. From 193 million asthma sufferers worldwide, ABPA prevalence in asthma is estimated between the extremes of 1.35–6.77 million sufferers, using 0.7–3.5% attrition rates. A compromise at 2.5% attrition has also been proposed, placing global burden at around 4.8 million people affected. The Eastern Mediterranean region had the lowest estimated prevalence, with a predicted case burden of 351,000; collectively, the Americas had the highest predicted burden at 1,461,000 cases. These are likely underestimates of total prevalence, given the exclusion of CF patients and children from the study, as well as diagnostic testing being limited in less developed regions.

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

The disease affects between 1 per 1000 and 1 per 250,000 adults. The disease is more common in women and increases as people age. It became less common since the 1950s, with the introduction of antibiotics. It is more common among certain ethnic groups such as indigenous people.

The exact rates of bronchiectasis are often unclear as the symptoms are variable. Rates of disease appeared to have increased in the United States between 2000 and 2007.

Interventions include intravenous (IV) medications (e.g. magnesium sulfate), aerosolized medications to dilate the airways (bronchodilation) (e.g., albuterol or ipratropium bromide/salbutamol), and positive-pressure therapy, including mechanical ventilation. Multiple therapies may be used simultaneously to rapidly reverse the effects of status asthmaticus and reduce permanent damage of the airways. Intravenous corticosteroids and methylxanthines are often given. If the person with a severe asthma exacerbation is on a mechanical ventilator, certain sedating medications such as ketamine or propofol, have bronchodilating properties. According to a new randomized control trial ketamine and aminophylline are also effective in children with acute asthma who responds poorly to standard therapy.

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 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.

DPB has its highest prevalence among the Japanese, at 11 per 100,000 population. Korean, Chinese, and Thai individuals with the disease have been reported as well. A genetic predisposition among East Asians is suggested. The disease is more common in males, with the male to female ratio at 1.4–2:1 (or about 5 men to 3 women). The average onset of the disease is around age 40, and two-thirds of those affected are non-smokers, although smoking is not believed to be a cause. The presence of HLA-Bw54 increases the risk of diffuse panbronchiolitis 13.3-fold.

In Europe and the Americas, a relatively small number of DPB cases have been reported in Asian immigrants and residents, as well as in individuals of non-Asian ancestry. Misdiagnosis has occurred in the West owing to less recognition of the disease than in Asian countries. Relative to the large number of Asians living in the west, the small number of them thought to be affected by DPB suggests non-genetic factors may play some role in its cause. This rarity seen in Western Asians may also be partly associated with misdiagnosis.

Shortness of breath is the primary reason 3.5% of people present to the emergency department in the United States. Of these individuals, approximately 51% are admitted to the hospital and 13% are dead within a year. Some studies have suggested that up to 27% of people suffer from dyspnea, while in dying patients 75% will experience it. Acute shortness of breath is the most common reason people requiring palliative care visit an emergency department.

Diagnosis of obstructive disease requires several factors depending on the exact disease being diagnosed. However one commonalty between them is an FEV1/FVC ratio less than 0.7, i.e. the inability to exhale 70% of their breath within one second.

Following is an overview of the main obstructive lung diseases. "Chronic obstructive pulmonary disease" is mainly a combination of chronic bronchitis and emphysema, but may be more or less overlapping with all conditions.

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

Reactive airway disease is a group of conditions that include reversible airway narrowing due to an external stimulation. These conditions generally result in wheezing.

Conditions within this group include asthma, chronic obstructive pulmonary disease, and viral upper respiratory infections.

The term reactive airway disease may be used in pediatrics to describe an asthma-like syndrome in infants too young for diagnostic testing such as the bronchial challenge test. These infants may later be confirmed to have asthma following testing. The term is sometimes misused as a synonym for asthma.