Environmental Factors In Asthma

Environmental factors in early life of an individual may determine which atopic individual may develop asthma in later life. This postulation is made due to observation that there is increasing prevalence of asthma in developing countries in recent few decades. Environmental factors may be playing along with genetic predisposition in causation of asthma.

There are various environmental factors implicated in causation (at least to some extent) of asthma such as hygiene, diet, allergen, air pollution, occupational exposure etc.

Hygiene in causation of asthma:

It is also known as hygiene hypothesis of asthma causation. This thesis developed from observation that, asthma incidence is less common among children with older siblings, because of lower incidence of infection among them in affluent societies. Hygiene hypothesis proposes that lower incidence of infection in early childhood leads to predominantly TH2 protective response, whereas frequent exposure to infection and endotoxins during childhood leads to TH1 protection.

Diet in causation of asthma:

The role of diet in asthma is controversial. Various observations suggest that diet low in antioxidants (e.g. vitamin C, vitamin A, selenium, magnesium etc.) and omega-3 polyunsaturated fatty acids found in fish oil, increase risk of asthma. However, dietary interventional studies do not support this observation. However, obesity is a factor in asthma, the mechanism of which is not clear.

Allergens in causation of asthma:

Inhaled allergen is the most common trigger for asthma and atopic sensitization. Exposure to house dust mites are implicated for asthma, especially in affluent and cold areas, where there is central heating system, with poor ventilation and carpeting, which encourages house dust mites. However, rigorous avoidance of allergen (house dust) has not shown to reduce risk of asthma. Pets, especially pet cats are also implicated for asthma.

Air pollution in asthma:

One of the important factors in increasing incidence of asthma, world over is increasing air pollution and pollutants such as sulfur dioxide, ozone, diesel particulates and many others suspended particulate matters. Air pollutants are common triggers for asthma. The strongest point who consider air pollution as an important causative factor is the fact that asthma is much more common in cities in compare to rural areas, where pollution level in much less. However, there are many examples available where asthma is less common in cities than rural areas.

Occupational exposure in causation of asthma:

Asthma due to occupational exposure can affect as many as 10% of young adults. There are more than 200 sensitizing agents (chemicals) identified to have role in asthma, such as diisocyanate and trimellitic anhydride. Exposure to the sensitizing agents can lead to development of asthma even in non-atopic individuals.


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