I’ve written here a couple of times before about variants of the “hygiene hypothesis” — the idea that our environments, which are extraordinarily clean by evolutionary standards, are keeping some children’s immune systems from developing normally, because they are not exposed to the range of microorganisms that the immune system needs to “see” in order to calibrate itself. I’ve also mentioned concerns about triclosan, an anti-bacterial and anti-fungal agent that is used in a wide variety of consumer products and cosmetics.
The PhysOrg.com site has a report of a study, conducted at the University of Michigan School of Public Health, which examines the effects of exposure to triclosan and bisphenol-A [BPA] (found in many plastics, and in carbonless receipt tapes) on the immune system. Both of these chemicals are classified as endocrine-disrupting compounds, and it has been suspected that they have an adverse effect on the immune system.
Using data from the 2003-2006 National Health and Examination Survey, U-M researchers compared urinary BPA and triclosan with cytomegalovirus (CMV) antibody levels and diagnosis of allergies or hay fever in a sample of U.S. adults and children over age 6. Allergy and hay fever diagnosis and CMV antibodies were used as two separate markers of immune alterations.
The paper is being published in the journal Environmental Health Perspectives, and is available online [abstract, with download link to full text].
The study found that, among people 18 and younger, higher exposures to triclosan were associated with a higher likelihood of allergies or hay fever. People over 18 with higher exposures to BPA showed higher CMV antibody levels, which suggests a potential problem with cell-mediated immunity. This effect seemed to depend on age, with different results for people under 18.
The results for triclosan seem to lend some additional support to the hygiene hypothesis
“The triclosan findings in the younger age groups may support the ‘hygiene hypothesis,’ which maintains living in very clean and hygienic environments may impact our exposure to micro-organisms that are beneficial for development of the immune system,” said Allison Aiello, associate professor at the U-M School of Public Health and principal investigator on the study..
AS the article point out, one limitation of the study is that it was essentially cross-sectional; that is, it measured both exposure and immune system impact over the same time period. A longitudinal study that tracked a group of people over a number of years would probably help clarify the effects.
Nonetheless, this is an interesting result, which lends credence to the idea that our well-intentioned efforts to improve hygiene may, like so many other well-intentioned efforts, have unexpected consequences.