Indoors, not Outdoors

My post on the lack of correlation between air pollution (in the form of ozone and particulates) and asthma has led several people to ask me -- well, what else could possibly be causing the rise in asthma cases?

One "cause" for increases in measured disease rates that almost always plays a role in modern epidemiology is better diagnosis and reporting.  There have been a number of diseases where changes in definitions and better diagnosis have led to an increase in reported cases, while the actual occurance rate has remained constant.  The rise in asthma cases seems to go beyond this effect.

The best guess I have for the increase in
asthma in this country, and the strong positive correlation between
asthma and economic development, is that it has something to do with
indoor pollution.  The spike in asthma cases seems to parallel the rise
in energy prices.  Beginning in the 1970's, we began sealing up houses
tighter and tighter to conserve energy.  Increasing penetration of air
conditioning simultaneously caused people to close the windows.  The spread of office-type service work had brought more people indoors.  I am
convinced its something inside, not outside, that is causing the asthma spike.

Update:  More on the lack of correlation between air pollution and asthma here, this time in California.


  1. JEH:

    One counterintuitive reason may well be how clean our world is. The body's immune system needs to be challenged to be healthy. With so many childhood diseases gone (vaccinated against), and the general cleanliness levels many people tend to maintain (antibacterial soaps, washing clothes frequently, insulating kids from, well, everything) the immune system may overreact, leading to increased incidences of allergies and asthma. This may not fully explain the increased incidence, especially at lower socio-economic levels, but I believe it is one factor.

  2. Tom Dilatush:

    Continuing the thought in the previous comment... There have been a couple of studies, widely reported (Google it!), that show a negative correllation between being raised on a farm and asthma. Refinements of these studies are showing exactly what the previous commenter speculated on: that early exposure to a wide variety of substances (and, presumably, viri and bacteria) helps build the immune system and reduces the incidence of asthma...

  3. JGH:

    Talk about correlation not necessarily causation!

    People are inside more. Hypothesis. Your previous commenters almost certainly explain SOME of the increase. Increased reporting does explain some as well -- but not nearly all. Actually, increased reporting explains only a small amount.

    Let's face it ... there are quite a few hypotheses, but little in the way of science to back any of them up. That's science. It is an empiric problem, with an empiric answer to be found. Let's not get ahead of ourselves with speculation (Isn't that the original issue, anyway?)

  4. Chris:

    I think that improved medicine is also attributing to the rise in some diseases. Call it reverse selection. As we allow people with diseases/conditions to live better lives they are more likely to pass those deficiencies onto their children whereas in the past they would have died/been very sick and not married/had kids.