Why Asthma Is on the Rise

Contrary to expectations, asthma rates have skyrocketed in urban areas in the U.S. that are not particularly clean; respiratory infections in early childhood may actually be a risk factor for it.

What's the Most Recent Development?

The hygiene hypothesis states that exposure in early childhood to infectious agents programs the immune system to mount differing highly effective defenses against disease-causing viruses, bacteria and parasites. While the hypothesis holds true in the case of allergies, according to the most recent research, it does not hold for asthma. Why? "Asthma is a much more complex condition than anyone has truly appreciated. Indeed, it may not be even be a single disease. Studies now suggest that only half of asthma cases have an allergic component."

What's the Big Idea?

Rising asthma rates contradict a mainstay of disease research: the hygiene hypothesis, first described in 1989 by David P. Strachan, a British epidemiologist who was studying hay fever. "The more children in a family, he noticed, the lower the rates of hay fever and eczema, an allergic skin condition. Children in large families tend to swap colds and other infections more often than children with fewer siblings. Could it be that increased exposure to pathogens from their many siblings was protecting children from large families against allergies?"

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