Questions and Answers:

1. What causes a sensitivity to a particular allergen or irritant?

There is a genetic predisposition in some individuals to become immunologically sensitized to different aeroallergens, like cat or house dust mite. The exact mechanism responsible for this genetic predisposition is unknown. It may have to do with the genetic predisposition to have inflammation of the lungs to begin with, which would make it easier for people to become sensitized and induce an immune response against things that they inhale. But this is an active area of research: while we know that the genetic predisposition is there and that it has a strong influence, we don’t know how it is linked to the sensitization process.

2. Briefly, would you explain why asthma and allergies are two distinct disorders, when they are so closely linked?

Asthma is related to inflammation in the airways of the lungs, while allergies result in inflammation of the eyes, skin or nose. Where the inflammation occurs determines whether it’s asthma or something else. Also, many people have both allergies and asthma, and the allergies can enhance the risk of having asthma. On the other hand, you can have allergies and not have a manifestation in the lungs. And you can also have asthma without having allergies. For example, for some kinds of asthma in the workplace, you can become sensitized to a chemical without a history of allergies whatsoever. Yet with repeated exposure to a chemical, you can develop this immunological response or sensitization anyway.

Asthma is such a complex — and confusing — topic because there are many different types of it: with or without allergies, as a result of airway damage from high-level exposure to a chemical, or even as a result of damage done by severe bronchitis.

3. Do pollutants cause allergies? That is, can they be allergens in the same way that house dust mite is an allergen?

This is very unlikely. The gases, the air pollutants like sulphur dioxide and ozone, can in and of themselves cause airway inflammation. But we’re not aware of anyone becoming truly allergic to any of these materials. These material are irritants, and they are much more likely to potentiate asthma in someone who already has a predisposition. For instance, many people think that they’re allergic to cigarette smoke, because every time they get exposed, they get their asthma. But for almost everyone, this is due to the irritant effect of the smoke and not to an allergy. People who have asthma are more sensitive to these irritants — sometimes exquisitely so, but it is not allergy.

4. In your paper you mention that asthma is much more prevalent among blacks than whites. Are your observations on the prevalence of cockroach allergen in the inner city relevant to this statistic?

We don’t really understand all of the epidemiology. Core inner-city people are more likely to have problems with cockroach allergy, and when you go up the social ladder between blacks and whites, the two groups do seem to have different patterns of sensitization. However, accounting for this is also complex and probably depends on factors such as location. Presumably, some years ago here in the northeastern U.S. when heating became much more expensive, people started living in more crowded conditions and had more carpeting and bedding, which increased the population of house dust mites and sensitization to them, which in turn increased the risk of asthma — which came to be seen as an inner city problem.

In a city like Atlanta, Georgia, the environment is very different from the northeast; it’s very wet and humid. The observation made about Atlanta is an interesting one, but as to why sensitization to cockroach is more prevalent there as opposed to house dust mite is still an open question.

Editorial:

This study makes it clear that the environment is a very important factor in asthma, and that different problems occur in different regions and population groups. It’s a very complicated area, in which there are no simple answers. One major aspect that we tried to present in the paper was that while the environment can be a cause of asthma, it can also be a trigger for it, independent of a causative factor. For instance, air pollution doesn’t cause asthma, as best we can tell, but you rarely get exacerbations of asthma outdoors unless you’re exercising — the air pollution worsens the existing asthma. The message here is that the environment is important both in causing and potentiating asthma.

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