[4] Asthma occurs when allergens, pollen, dust, or other particles, are inhaled into the lungs, causing the bronchioles to constrict and produce mucus, which then restricts oxygen flow to the alveoli.

[22] During recovery from an asthma attack (exacerbation), the sputum may appear pus-like due to high levels of white blood cells called eosinophils.

[25] A number of other health conditions occur more frequently in people with asthma, including gastroesophageal reflux disease (GERD), rhinosinusitis, and obstructive sleep apnea.

[60] Common indoor allergens include dust mites, cockroaches, animal dander (fragments of fur or feathers), and mould.

[63][64] Weak evidence suggests that efforts to decrease mould by repairing buildings may help improve asthma symptoms in adults.

[20] 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.

[67][68] 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.

[82][83] Several factors may be at play including decreased respiratory function due to a buildup of fat and the fact that adipose tissue leads to a pro-inflammatory state.

[90] Home factors that can lead to exacerbation of asthma include dust, animal dander (especially cat and dog hair), cockroach allergens and mold.

This might reflect a combination of factors, including poor treatment adherence, increased allergen and viral exposure, and altered immune tolerance.

[20] It is defined by the Global Initiative for Asthma as "a chronic inflammatory disorder of the airways in which many cells and cellular elements play a role.

The chronic inflammation is associated with airway hyper-responsiveness that leads to recurrent episodes of wheezing, breathlessness, chest tightness and coughing particularly at night or in the early morning.

[5][20] Asthma may be suspected if there is a history of recurrent wheezing, coughing or difficulty breathing and these symptoms occur or worsen due to exercise, viral infections, allergens or air pollution.

[109] While these are the primary symptoms of asthma,[110] some people present primarily with coughing, and in severe cases, air motion may be significantly impaired such that no wheezing is heard.

A few hundred different agents have been implicated, with the most common being isocyanates, grain and wood dust, colophony, soldering flux, latex, animals, and aldehydes.

[125] AERD consists of asthma, nasal polyps, sinus disease, and respiratory reactions to aspirin and other NSAID medications (such as ibuprofen and naproxen).

[140] According to European Respiratory Society, it may not be suitable to label wheezing preschool children with the term asthma because there is lack of clinical data on inflammation in airways.

[141] In adults, COPD, congestive heart failure, airway masses, as well as drug-induced coughing due to ACE inhibitors may cause similar symptoms.

However, this level of investigation is not performed due to COPD and asthma sharing similar principles of management: corticosteroids, long-acting beta-agonists, and smoking cessation.

[145] The World Health Organization recommends decreasing risk factors such as tobacco smoke, air pollution, chemical irritants including perfume, and the number of lower respiratory infections.

If mild persistent disease is present (more than two attacks a week), low-dose inhaled corticosteroids or alternatively, a leukotriene antagonist or a mast cell stabilizer by mouth is recommended.

These interventions may also reduce the number of days children experience asthma symptoms and may lead to small improvements in asthma-related quality of life.

[226] Whether or not stopping LABA increases the risk of serious adverse events or exacerbations requiring an emergency department visit or hospitalization is uncertain.

Various approaches have been undertaken to try and improve adherence to treatments to help people prevent serious asthma exacerbations including digital interventions.

In people with mild to moderate asthma, treatment with vitamin D supplementation or its hydroxylated metabolites does not reduce acute exacerbations or improve control.

[268][269] Air ionizers show no evidence that they improve asthma symptoms or benefit lung function; this applied equally to positive and negative ion generators.

[270] Manual therapies, including osteopathic, chiropractic, physiotherapeutic and respiratory therapeutic manoeuvres, have insufficient evidence to support their use in treating asthma.

[298] In 1873, one of the first papers in modern medicine on the subject tried to explain the pathophysiology of the disease while one in 1872, concluded that asthma can be cured by rubbing the chest with chloroform liniment.

[309] As these psychoanalysts interpreted the asthmatic wheeze as the suppressed cry of the child for its mother, they considered the treatment of depression to be especially important for individuals with asthma.

His lawyers had argued that the dangerous levels of pollution in Bangladesh could possibly lead to worsening of his health condition, or even premature death.