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Asthma risk factors

It is not always clear why some people develop asthma while others don't. However, there are some known asthma risk factors:


Childhood asthma occurs more frequently in boys than in girls. It is unknown why this occurs although some experts find a young male's airway size is smaller when compared with the female's airway, which may contribute to increased risk of wheezing after a cold or other viral infection. Around age 20, the ratio of asthma between men and women is the same. In adulthood more females than males have asthma.

Family history

Your inherited genetic makeup may predispose you to having asthma. In fact, it is thought that three-fifths of all asthma cases are hereditary. According to a report from the US Centers for Disease Control, if a person has a parent or parents with asthma, he or she is two to six times more likely to develop asthma than someone who does not have a parent with asthma.

Airway hyper-reactivity

It appears that having airway hyper-reactivity is another risk factor for asthma, although researchers are not sure why this is true. In asthma, the airways are hyperreactive and become inflamed when they meet such asthma triggers as allergens or cold air. Not all people with airway hyper-reactivity develop asthma, but in those who do have it, the airway hyper-reactivity appears to increase the risk of asthma.


Atopy means a genetic predisposition that increases a person’s risk of developing certain allergic conditions such as eczema ( atopic dermatitis), allergic rhinitis, allergic conjunctivitis and asthma.

Studies indicate that 40 to 50% of children with eczema or atopic dermatitis develop asthma. Some findings indicate that children with atopic dermatitis may have more severe and persistent asthma as adults.


Allergies and asthma often co-exist. Indoor allergies are a predictor of who might be at risk of an asthma diagnosis. One nationwide study showed levels of bacterial toxins called endotoxins in house dust were directly related to asthma symptoms and the use of asthma inhalers, bronchodilators, and other asthma medications.

Sources of other indoor allergens include animal proteins (particularly cat and dog allergens), dust mites, cockroaches and fungi. Changes that have increased house insulation over the years are thought to increase exposure to these causes of asthma, thereby increasing the prevalence of asthma.

Environmental factors

Indoor air pollution such as cigarette smoke, mould, and noxious fumes from household cleaners and paints can cause allergic reactions and asthma. Environmental factors such as pollution, sulphur dioxide, nitrogen oxide, ozone, cold temperatures, and high humidity are all known to trigger asthma in susceptible individuals. In fact, asthma symptoms and hospital admissions are greatly increased during periods of heavy air pollution.

Ozone is the major destructive ingredient in smog. It causes coughing, shortness of breath and even chest pain -- and can increase susceptibility to infection. Sulphur dioxide, another component of smog, also irritates the airways and constricts the air passages, resulting in asthma attacks.

Gas cookers are the primary source of indoor nitrogen dioxide. Studies show that people who cook with gas are more likely to have wheezing, breathlessness, asthma attacks and hayfever than those who cook with other methods. Weather changes can also result in asthma attacks in some people. For instance, cold air causes airway congestion, bronchoconstriction, secretions, and decreased mucociliary clearance. Increases in humidity may also cause breathing difficulties in certain people.

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