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Inner-city asthma and the hygiene hypothesis
Paolo M Matricardi1, Gabriel R Bouygue, Salvatore Tripodi
1Institute of Neurobiology and Molecular Medicine, Italian National Research Council, Rome, Italy. matricardip@who.int
Summary
The hygiene hypothesis explains rising asthma rates, suggesting reduced early-life infection exposure due to Westernization. Inner-city asthma in the US may represent a late stage of this trend, affecting disadvantaged populations.
Area of Science:
- Epidemiology
- Allergology
- Public Health
Background:
- The hygiene hypothesis posits that reduced exposure to infections in early life increases the risk of atopy and asthma.
- Westernization and improved hygiene have been linked to rising rates of allergic diseases globally.
- The 'inner-city asthma' phenomenon in the United States presents a complex case, seemingly contradicting the hypothesis.
Purpose of the Study:
- To compare the rise of asthma, hay fever, and atopic sensitization in Europe and the United States.
- To analyze the 'inner-city asthma' phenomenon within the context of the hygiene hypothesis.
- To explore the historical and socioeconomic factors influencing allergic disease trends.
Main Methods:
- Review of historical descriptions of respiratory allergies.
- Analysis of current scientific literature on asthma, hay fever, and atopic sensitization.
- Synthesis of epidemiologic evidence and expert judgment for data selection.
Main Results:
- The hygiene hypothesis, linking reduced early-life infections to increased allergies, emerged from European studies.
- In the US, asthma has increased since the 1970s, particularly among impoverished minority groups in inner cities.
- This US trend may reflect Westernization's impact, with declining exposure to infections cascading through socioeconomic strata over time.
Conclusions:
- Inner-city asthma in the US could be the culmination of a two-century-long process of urbanization and Westernization.
- The historical trajectory suggests a class-driven pattern in the rise of respiratory allergies.
- Understanding these trends requires considering socioeconomic factors and the evolving nature of hygiene and infection exposure.