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• Household chemicals and persistent wheeze: Is there a link?
  Andrew N Williams
  Published on: 1 March 2006

• Published on: 1 March 2006

  Household chemicals and persistent wheeze: Is there a link?

  • Andrew N Williams, Director General

  Dear Editor,

  Sherriff and colleagues report an apparent association between mothers’ self-reported frequency of use of assorted household ‘chemicals’ during pregnancy and ‘persistent wheeze’ in their offspring. Since their paper suggests this may help explain recent rises in asthma, the robustness of the data and other explanations for the observed statistical association need careful consideration.

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  Dear Editor,

  Sherriff and colleagues report an apparent association between mothers’ self-reported frequency of use of assorted household ‘chemicals’ during pregnancy and ‘persistent wheeze’ in their offspring. Since their paper suggests this may help explain recent rises in asthma, the robustness of the data and other explanations for the observed statistical association need careful consideration.

  We see several concerns, including both exposure and outcome measures, lack of a plausible biological mechanism for the suggested in utero effect, and the possibility of both recall and selection bias.

  The definition of persistent wheeze is weak, and far removed from criteria currently considered to define asthma . Offspring are categorised as having ‘persistent wheeze’ if mothers’ responses indicate one instance of wheezing in three consecutive 12 month periods.

  It is curious that the association appears using frequency of use scores which treat 11 disparate product types as equal, irrespective of composition, and remains when each in turn was removed from the analysis. Some product types have nothing at all in common: we can see no significant ingredient that is common even to the majority, nor any likely shared toxic mode of action. Contrary to the authors’ suggestion formaldehyde is little used in the products surveyed.

  Self-reported frequency of use is a very poor measure of exposure: variations in quantity of product used, duration of use and routes of exposure (inhalation, dermal, ingestion etc) can yield scores which run contrary to actual exposure.

  We see little justification for aggregating disparate product exposures as ‘Total Chemical Burden’ by analogy with particulate air pollution: the action of particulates is plausibly associated more with size, geometry and/or absorptive capacity than with chemical composition. This concept cannot simply be extrapolated to vapours or non-particulates, and the term itself unfortunately suggests some absorbed, retained load: ‘sum of reported product use frequencies’ would have been more appropriate.

  We are not aware of any substantiated toxicological effect that is shared by all chemicals irrespective of composition, especially given that the notion of a ‘chemical’ is essentially subjective. All matter, natural or synthetic, is composed of atoms and molecules. How do the products considered differ from the many household chemicals not considered, and chemicals that make up the natural environment to which people are continuously exposed?

  It seems unlikely that the association is driven by one product type since it remained when each in turn was removed from the analysis. Further, previous analyses of these questionnaires for two specific types (aerosols and air fresheners) found no association with wheeze . Per capita consumption of cleaning products in different European countries also shows no correlation with the patterns of asthma .

  Other than chance, how else might the observed association have arisen? Apart from confounding by other chemicals in the built or natural environment, certain mothers may have over-reported both chemical use and wheezing symptoms. While ‘chemicals’ are heterogeneous in terms of composition and toxicology, the term perhaps has some homogeneous psychological significance for certain people. We understand the question about frequency of use was headed “Chemicals …… in your environment”.

  The authors acknowledge some selection bias: “those excluded from the analysis due to lack of chemical use data were more likely to have wheezed at all ages than those included, and those excluded from the analysis due to missing symptom data had, on average, higher TCB scores than those in the analysis”. This is potentially significant since the numbers excluded from the study for missing data (50%) are large.

  Scrutinising household products for any possible role in the rise in asthma is important but, to be meaningful, exposures must be properly defined. --------------------------------

  References

  1.Sherriff A, Farrow A, Golding A, the ALSPAC Study Team, Henderson J. Frequent use of chemical household products is associated with persistent wheezing in pre-school age children. Thorax 2005; 60: 45-49

  2.Asher MI and Weiland SK on behalf of the ISAAC Steering Committee (1998) The International Study of Asthma and Allergies in Childhood (ISAAC). Clin Exp Allergy 28, Suppl 5, 52-66.

  3. Farrow A, Taylor H, Northstone K, Golding J. Symptoms of Mothers and Infants Related to Total Volatile Organic Compounds in Household Products. Arch Environ Health. 2003 Oct;58(10):633-41.

  4. Pickup J. Trends in home and consumer hygiene. In 'Are we too clean? - a question of immunity balance'. RIPH Symposium Report. Published as a supplement to Health & Hygiene. London: Royal Institute of Public Health 2003: 6-7.

  Dr A N Williams
  Director General UKCPI

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  Conflict of Interest:
  None declared.

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