The health effects of formaldehyde have been a matter of scientific and particularly allergologic concern for decades. Recently, Garrett et al. proposed that low-level indoor exposure to formaldehyde may increase the risk of sensitization to common aeroallergens in children ( 1). However, this hypothesis must be critically discussed for several reasons:
Of the 148 children studied, 33% were exposed to passive smoking. Unfortunately, no exact information is given on the proportion of atopic or asthmatic children in the exposed group. Since tobacco smoke with its numerous volatile compounds may contribute about 50% of indoor formaldehyde levels ( 2), and may lead to formaldehyde concentrations of up to 2100 ppb ( 3–5), it would have been helpful to determine whether the confounding factor in the study was: formaldehyde or environmental tobacco smoke. In this context, it is noteworthy that postnatal environmental exposure to tobacco smoke in children leads to significant respiratory, but not allergic/atopic, symptoms and morbidity ( 6–8).
The highest exposure values to formaldehyde are encountered in occupational settings, but, so far, in this context, formaldehyde has not been proven to be an important cause of immunologically mediated respiratory disease ( 9, 10). In addition, an expert panel recently found no evidence that patients could be sensitized by inhalation exposure ( 11). It was therefore concluded that there is not sufficient evidence to classify formaldehyde as a cause of asthma, according to the official European Union criteria ( 12). Moreover – and this is a very important finding for this discussion – an indoor level beyond 100 ppb, as reported by Garrett et al. ( 1), seems to prevent respiratory irritation in exposed persons, a proposed mechanism for sensitization to aeroallergens facilitated by formaldehyde ( 11).
Unquestionably, the causes of the increasing prevalence of atopic sensitization need to be elucidated. But before far-reaching health risks in the developed world can be attributed to the speculated effects of some indoor pollutants, one should be aware of the numerous pitfalls in finding and interpreting the potential effects of variables affecting the prevalence of atopic disorders ( 13).
In summary, the presented data are not convincing evidence of an increased risk of atopic allergies in children exposed to low-level indoor formaldehyde.