Impacts of Outdoor and Indoor Air Pollution on Allergic Airway Disease in India
Prof SK Chhabra
Consultant Pulmonologist
Head, Department of Crdiorespiratory Physiology,
Vallabhbhai Patel Chest Institute
Delhi - 110007
There is worldwide concern over the possible adverse effects of short-term and longterm exposure to ambient concentrations of several air pollutants such as particulates, ozone,
oxides of nitrogen and sulfur dioxide. Studies published from several developed countries to
date have given definite evidence on the effects of these pollutants on the occurrence of
respiratory symptoms and diseases in the general population. While evidence to suggest that
exposure to these pollutants leads to aggravation of symptoms and deterioration of lung
function in patients with asthma and chronic obstructive lung disease is substantial and more
definitive, there is considerable uncertainty regarding the long-term health effects in the
general population. Whether rising air pollution has contributed to increasing prevalence of
respiratory allergic disorders has remained a debatable issue. While aggravation of allergies
on exposure to diesel exhaust has some experimental support, its clinical relevance is open to
question.
Developing countries like India are faced with increasing levels of outdoor air
pollution with increasing economic activity. The outdoor air in large metropolitan cities of
India is one of the worst in the world. Vehicles constitute the major source of outdoor air
pollution in urban areas, accounting for nearly two-thirds of the total pollutant load.
Industries and domestic sources contribute the rest. In India, data on health effects of outdoor
air pollution is limited. Most of the studies carried out in India have looked at the association
between acute or chronic respiratory symptoms with air quality, mainly focusing on
particulates. Specifically, the impact on respiratory allergies has received little attention. In
recent years, air quality data shows increasing levels of oxidant pollutants, such as oxides of
nitrogen and the secondary pollutant, ozone. So far, there have been no studies on the effect
of ozone on respiratory allergies in human subjects in India. Recently, in a guinea pig model
of asthma, it has been shown by the author that a two-hour daily exposure of sensitized
animals to ambient concentrations of ozone potentiated the effect of allergens on the airways.
More than half of Indian households use biomass fuels (crop residues, wood, cow
dung) as energy sources for cooking, not only in rural areas but also in urban areas. The
residents of these households face the additional problem of indoor air pollution that often
exceeds outdoor pollution. Oxides of nitrogen are the other major component of the indoor
air pollution. The effect of indoor air pollution on respiratory allergies has not been
investigated in any detail although a few studies have looked at the prevalence of asthma in
relation to use of biomass fuels, but with conflicting or equivocal results. While there have
been several studies on the prevalence of asthma in children and adults, outdoor or indoor air
quality has not been investigated as a risk factor. There is a need to conduct studies on the
impact of current ambient air quality on the prevalence and clinical aspects of respiratory
allergic disorders in India.