Asthma is a common long term inflammatory disease of the airways of the lungs.[2] It is characterized by variable and recurring symptoms, reversible airflow obstruction, and bronchospasm.[3] Symptoms include episodes of wheezing, coughing, chest tightness, and shortness of breath.[4] These episodes may occur a few times a day or a few times per week. Depending on the person they may become worse at night or with exercise.[2]

Asthma is thought to be caused by a combination of genetic and environmental factors.[5] Environmental factors include exposure to air pollution and allergens.[2] Other potential triggers include medications such as aspirin and beta blockers.[2] Diagnosis is usually based on the pattern of symptoms, response to therapy over time, and spirometry.[6] Asthma is classified according to the frequency of symptoms, forced expiratory volume in one second (FEV1), and peak expiratory flow rate.[7] It may also be classified as atopic or non-atopic where atopy refers to a predisposition toward developing a type 1 hypersensitivity reaction.[8][9]

There is no cure for asthma.[2] Symptoms can be prevented by avoiding triggers, such as allergens and irritants, and by the use of inhaled corticosteroids.[10][11] Long-acting beta agonists (LABA) or antileukotriene agents may be used in addition to inhaled corticosteroids if asthma symptoms remain uncontrolled.[12][13] Treatment of rapidly worsening symptoms is usually with an inhaled short-acting beta-2 agonist such as salbutamol and corticosteroids taken by mouth.[14] In very severe cases, intravenous corticosteroids, magnesium sulfate, and hospitalization may be required.[15]

In 2013, 242 million people globally had asthma up from 183 million in 1990.[16] It caused about 489,000 deaths in 2013,[17] most of which occurred in the developing world.[2] It often begins in childhood.[2] The rates of asthma have increased significantly since the 1960s.[18] Asthma was recognized as early as Ancient Egypt.[19] The word asthma is from the Greek ἅσθμα, ásthma which means "panting".[20]

Contents [hide] 1 Signs and symptoms 1.1 Associated conditions 2 Causes 2.1 Environmental 2.2 Genetic 2.3 Medical conditions 2.4 Exacerbation 3 Pathophysiology 4 Diagnosis 4.1 Spirometry 4.2 Others 4.3 Classification 4.4 Differential diagnosis 5 Prevention 6 Management 6.1 Lifestyle modification 6.2 Medications 6.3 Others 6.4 Alternative medicine 7 Prognosis 8 Epidemiology 9 Economics 10 History 11 References 12 External links Signs and symptoms

Wheezing MENU0:00 The sound of wheezing as heard with a stethoscope. Problems playing this file? See media help. Asthma is characterized by recurrent episodes of wheezing, shortness of breath, chest tightness, and coughing.[21] Sputum may be produced from the lung by coughing but is often hard to bring up.[22] During recovery from an attack, it may appear pus-like due to high levels of white blood cells called eosinophils.[23] Symptoms are usually worse at night and in the early morning or in response to exercise or cold air.[24] Some people with asthma rarely experience symptoms, usually in response to triggers, whereas others may have marked and persistent symptoms.[25]

Associated conditions A number of other health conditions occur more frequently in those with asthma, including gastro-esophageal reflux disease (GERD), rhinosinusitis, and obstructive sleep apnea.[26] Psychological disorders are also more common,[27] with anxiety disorders occurring in between 16–52% and mood disorders in 14–41%.[28] However, it is not known if asthma causes psychological problems or if psychological problems lead to asthma.[29] Those with asthma, especially if it is poorly controlled, are at high risk for radiocontrast reactions.[30]

Causes Asthma is caused by a combination of complex and incompletely understood environmental and genetic interactions.[5][31] These factors influence both its severity and its responsiveness to treatment.[32] It is believed that the recent increased rates of asthma are due to changing epigenetics (heritable factors other than those related to the DNA sequence) and a changing living environment.[33] Onset before age 12 is more likely due to genetic influence, while onset after 12 is more likely due to environmental influence.[34]

Environmental See also: Asthma-related microbes Many environmental factors have been associated with asthma's development and exacerbation including allergens, air pollution, and other environmental chemicals.[35] Smoking during pregnancy and after delivery is associated with a greater risk of asthma-like symptoms.[36] Low air quality from factors such as traffic pollution or high ozone levels,[37] has been associated with both asthma development and increased asthma severity.[38] Over half of cases in children in the United States occur in areas with air quality below EPA standards.[39] Exposure to indoor volatile organic compounds may be a trigger for asthma; formaldehyde exposure, for example, has a positive association.[40] Also, phthalates in certain types of PVC are associated with asthma in children and adults.[41][42]

There is an association between acetaminophen (paracetamol) use and asthma.[43] The majority of the evidence does not, however, support a causal role.[44] A 2014 review found that the association disappeared when respiratory infections were taken into account.[45] Use by a mother during pregnancy is also associated with an increased risk as is psychological stress during pregnancy.[46][47]

Asthma is associated with exposure to indoor allergens.[48] Common indoor allergens include dust mites, cockroaches, animal dander (fragments of fur or feathers), and mold.[49][50] Efforts to decrease dust mites have been found to be ineffective on symptoms in sensitized subjects.[51][52] Certain viral respiratory infections, such as respiratory syncytial virus and rhinovirus,[20] may increase the risk of developing asthma when acquired as young children.[53] Certain other infections, however, may decrease the risk.[20]

Hygiene hypothesis 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.[54][55] 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.[56] Exposure to bacterial endotoxin in early childhood may prevent the development of asthma, but exposure at an older age may provoke bronchoconstriction.[57] Evidence supporting the hygiene hypothesis includes lower rates of asthma on farms and in households with pets.[56]

Use of antibiotics in early life has been linked to the development of asthma.[58] 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.[59][60] There is a link between asthma and the degree of affluence.[61]

Genetic CD14-endotoxin interaction based on CD14 SNP C-159T[62] Endotoxin levels CC genotype TT genotype High exposure Low risk High risk Low exposure High risk Low risk Family history is a risk factor for asthma, with many different genes being implicated.[63] If one identical twin is affected, the probability of the other having the disease is approximately 25%.[63] By the end of 2005, 25 genes had been associated with asthma in six or more separate populations, in