Air pollution (outdoor as well as indoor - the offgassing from the myriad synthetic materials found in construction and furnishings these days) is only one trigger of asthma and not the only one exacerbated by modern society.<p>Many experts have theorized changes in our microbiota are partly responsible for the general rise in asthma over the past decades. That would include things like over-sanitation, increased C sections, antibiotics, gut flora-killing diet, etc.  <a href="http:&#x2F;&#x2F;www.everydayhealth.com&#x2F;asthma-pictures&#x2F;8-expert-theories-about-why-asthma-rates-are-rising.aspx" rel="nofollow">http:&#x2F;&#x2F;www.everydayhealth.com&#x2F;asthma-pictures&#x2F;8-expert-theor...</a>