Asthma and Allergy on the March :


Asthma and Allergy on the March
In recent weeks we’ve seen that the hygiene hypothesis is the best explanation yet for why allergies and asthma are increasing worldwide. In this final entry on this topic, let’s examine the pros and cons of this theory.
Several findings provide the best evidence in favor of the hygiene hypothesis. One is that children raised in farm environments, where they’re exposed to bacterial products from farm animals at an early age, are far less likely to develop hay fever and asthma than children who grow up in cities. Another is that children placed in day care environments during the first six months of life, where they’re exposed to a high number of infections, are protected from developing asthma later on.
But other studies have not consistently supported this theory. Viral infections like hepatitis do not seem to be protective. The presence of cats or dogs in the home was found to be protective in some studies but not in others. Endotoxin levels (a bacterial by-product) in the homes of newborns do not seem to be linked to the infants’ risk of developing asthma. Finally, the use of antibiotics in the first year of life, presumably reflecting bacterial infections in these infants, is associated with a lower risk of developing asthma and allergies in some, but not all, studies. So the validity of the hygiene hypothesis is still a subject of disagreement among allergists and epidemiologists.
Does the theory have any implications for how you should act to minimize the likelihood that your children or children-to-be will develop of asthma and allergic disorders? Personally, I don’t think so, at least not yet. Moving to a farm, taking in domestic animals, or putting your child in day care with a lot of infections are pretty drastic undertakings for, at best, marginal benefits.
If the hygiene hypothesis is correct, these environmental changes could decrease by two- to fourfold the chance that your infant will develop asthma. Still, most of the risk for asthma actually comes from inherited predispositions and from the allergen content in the indoor home environment. We have no control over the genetics of our children, but we can minimize their exposure to dust mites, molds, and furry animals in our homes. Yet even this is easier said than done. Many efforts to reduce allergen exposure in early childhood have failed to demonstrate clinical benefits, in part because it’s nearly impossible to eliminate these major indoor allergens entirely from our homes.
For the time being, you can watch from a distance as this fascinating inquiry into a well-founded hypothesis to explain the epidemic of asthma and allergies continues. It will be some time before what’s being learned in our research translates into specific medical recommendations that may help to turn around this pandemic. Until then, research on how the early life experiences of individual infants can influence the development of asthma and allergies is likely to benefit the next generation.