Is the hygiene hypothesis still a viable explanation for the increased prevalence of asthma?

Abstract

The hygiene hypothesis states that a reduced exposure to allergens in early life is solely implicated in the growing propensity for allergy sensitization. Important elements of the hypothesis include helminth infection, exposure to endotoxins, exposure to pets and growing up on a farm. However, the hygiene hypothesis alone does not provide an adequate explanation for the observed increase in allergic disease. For example, in North American inner cities, asthma is increasing among children who live in very poor housing, which might be assumed to be somewhat dirty. In order to explain the increase in asthma, we need to take a broader view and also consider alterations related to the adoption of a western lifestyle. It has been suggested that lifestyle changes related to obesity (e.g. a change in diet) are associated with asthma. Other changes include a progressive decrease in physical activity. This lifestyle factor seems to correlate best with the recent increase in asthma. Clearly, the link between physical activity and asthma needs to be investigated in more detail.

Allergic Rhinitis and its Impact on Asthma (ARIA) 2008*

“…Three major hypotheses have developed and explored the role of overt viral and bacterial infections, the significance of environmental exposure to microbial compounds and the effect of both on underlying responses of the innate and adaptive immunity. To date, a truly unifying concept has not yet emerged (1004) and there are some concerns about this hypothesis (1005).…”

“…• The link between physical activity, allergic diseases and asthma needs to be investigated in more detail (1005,1038). …”

In vitro diagnosis of allergy: how to interpret IgE antibody results in clinical practice

“…In this context, questions to ask the patient would include: In addition, more recent publications suggest that information regarding obesity, physical inactivity and time spent indoors may add to the precision of the diagnosis [5,6].…”

Environmental Pollutants and Pediatric Asthma

“…The hygiene hypothesis, as currently understood, does not provide an adequate explanation for the increase in allergic disease in North American inner cities, where asthma is increasing among children who live in very poor housing [25]. It is also known that those in the lowest social classes with the highest percentage of smokers are using domestic chemical cleaning products most frequently.…”