The Hygiene Hypothesis

Recent analyses of risk-factor patterns for allergic disease in Europe has led to a causal theory for the increasing asthma epidemic; this theory is known as the hygiene hypothesis. It stipulates that advances in hygiene have removed a protective influence against atopy and asthma that was once provided by infectious exposures in early childhood. This hypothesis has been questioned in the United States, where the largest sector of increasing asthma incidence since the 1970s occurs in the inner cities among minorities who are living in poverty with suboptimal hygienic conditions. When viewed from a historical perspective, the recent increasing trend in respiratory allergies among the less-advantaged in the United States may be explained as the consequence of several epiphenomena linked to Westernization (including declining exposure to foodborne and orofecal infections) that has moved downward from the richest socioeconomic strata to the poorest in the last 150 years.6 In regard to this theory, it has been suggested that exposing infants to factors that increase Th1 cells (infected siblings, day care attendance during the first six months of life, and avoidance of frequent antibiotic administration) may restore the T-helper subset balance, resulting in fewer incidences later in life of asthma and allergy. It appears that these exposures must occur prior to the first year of life to make a difference. Experimental use of mycobacterial strains has demonstrated a shift from Th2-immune responses to Thl-immune responses, thereby preventing the allergy development in mice, as well as ameliorating autoimmune diseases characterized by Th1 responses.7 It is interesting to note that both autoimmune and allergic diseases share a parallel increasing prevalence. Rebalance of the Th1- and Th2-subset cell ratios is a highly speculative theory because it does not explain fully the complete immunologic etiology of asthma and allergies.

Allergy Relief

Allergy Relief

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