Is good hygiene a risk factor for asthma?
The perception that asthma was less common in developing countries led to the “hygiene hypothesis”.6,7 The problem with this hypothesis is that there are many lines of evidence that do not fit.8 The most extensive body of evidence against the hypothesis comes from the ISAAC study,9 in which asthma was found to be unexpectedly prevalent in several countries with a relatively low standard of living. In collaboration with Venezuelan colleagues, we have found high levels of pro-inflammatory alleles, IgE and asthma in people living on Coche Island, in the Caribbean, with endemic parasitic disease and poor socioeconomic conditions.10 Some epidemiological studies have reported associations between increased infection and reduced asthma, but the results are not consistent in all studies.7 There is still too little evidence to conclude that good hygiene itself is an important risk factor for the high levels of asthma in affluent or “westernised” societies. Important, unrecognised factors are li
