**3.1.3 Occupational and environmental exposures**

Farming and occupations with dusty environments increase the risk of developing chronic bronchitis two to threefold and, in combination with smoking, the risk increases to almost sixfold above average population(Melbostad et al.,1997;Salvi & Barnes,2009 as cited in Shapiro SD,2010). Environmental particulate air pollution and indoor smoke from biomass fuels have also been linked to COPD (Tashkin et al.,1984). There is strong evidence of an association between outdoor pollution(particulate matter, O3,NO2) and decreased pulmonary function (Gauderman et al,2004,2007; Rojas-martinez et al.,2007 as cited in Shapiro SD,2010). Exposure to air pollutants, occupational exposure, second-hand smoke exposure, fumes from burning biomass fuel, etc can produce deleterious effects on the airway. Oxidative stress, pulmonary and systemic inflammation, reduction in airway ciliary activity, amplification of viral infections, and increases in bronchial reactivity could lead to irreversible loss of pulmonary function over time and COPD(ATS,2010).

#### **3.1.4 Gender**

Epidemiological studies shows a male gender predominance related to the higher cigarette smoking habit or other inhaled toxins and occupational exposure among men within a population(Buist et al,2007). Increase in smoking among women has diminished the difference among gender prevalence. Mortality may be peaking among men in the United States but, among women, mortality continues to rise and deaths from COPD among women now even exceeds those among men (Mannino et al.,2002,Silverman et al.,2000 as cited in Shapiro SD,2010).
