Genetics: Three-fifths of all asthma is hereditary — those with asthmatic parents are three to six times more likely to have it.
Gender: While boys are more likely to develop asthma due to narrower respiratory tracts, by adulthood, women report more severe asthma. The change occurs at puberty, University of Groningen scientists found in a study.
Obesity: Asthma is more common in overweight adults and children, who report more uncontrolled attacks and need more meds.
Indoor allergens: May include dust mites in beds, rugs and curtains, cockroaches, pet dander, and nitrogen dioxide from gas stoves.
Outdoor allergens: Allergic asthma may be set off by grass, tree and weed pollens, moulds, dust and animal dander.
Tobacco smoke: The Centres for Disease Control & Prevention says anyone exposed to second-hand smoke is at risk of asthma.
Chemical irritants: About 15 per cent of cases are occupational asthma, triggered by flour and grain dust, isocyanates (chemicals often found in spray paint), latex, animals and wood dust, according to the NHS.
Emotions: Roughly 69 per cent of patients said stress triggers their asthma, while half of all respondents in an American Thoracic Society study said laughter set off attacks. Anger and fear are other common emotional prompts.
Medications: From aspirin to other non-steroid anti-inflammatory drugs, and beta-blockers (which are used to treat high blood pressure, heart conditions and migraine)

M Sen and Keith J Fernandez

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