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Being too clean may lead to allergies, study suggests

Nov. 29, 2010
Courtesy of the University of Michigan
and World Science staff

Young peo­ple may suf­fer more al­ler­gies if they’re over­ex­posed to an­ti­bac­te­ri­al soaps with a com­mon in­gre­di­ent, tri­clo­san, a study in­di­cates.

The chem­i­cal is widely used in prod­ucts such as an­ti­bac­te­ri­al soaps, tooth­paste, pens, dia­per bags and med­i­cal de­vices.

The sci­en­tists cau­tioned that their anal­y­sis did­n’t clearly de­ter­mine cause-and-ef­fect rela­t­ion­ships. For ex­am­ple, some peo­ple might use more an­ti­bac­te­ri­al soaps be­cause they have more al­ler­gies, rath­er than the oth­er way around.

A model of the struc­ture of a mole­cule of tri­clo­san. Gray balls re­pre­sent atoms of car­bon; white balls, atoms of hy­dro­gen; green, chlo­r­ine; and red, oxy­gen. (Im­age cour­tesy USDA)

But the tri­clo­san find­ings may “sup­port the ‘hy­giene hy­poth­e­sis,’ which main­tains [that] 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 of the Uni­vers­ity of Mich­i­gan School of Pub­lic Health, prin­ci­pal in­ves­ti­ga­tor in the stu­dy.

The re­search al­so found that ex­cess ex­po­sure to Bi­sphe­nol A, a sub­stance found in many plas­tics and as a pro­tec­tive lin­ing in food cans, among adults may weak­en the im­mune sys­tem. Both chem­i­cals are in a class of tox­i­cants called endocrine-disrupting com­pounds, thought to af­fect health by mim­ick­ing or act­ing on hu­man hor­mones, said the re­search­ers.

The in­vest­i­gat­ors used da­ta from 2003 to 2006 gen­er­at­ed by a pre­vi­ous U.S. study known as the Na­tional Health and Nu­tri­tion Ex­amina­t­ion Sur­vey. They com­pared uri­nary Bi­sphe­nol A and tri­closan lev­els with di­ag­no­sis of al­ler­gies and with lev­els of an­ti­bod­ies to the path­o­gen cy­to­meg­a­lo­vir­us—both con­sid­ered signs of im­mune sys­tem changes.

Peo­ple over age 18 with high­er lev­els of Bi­sphe­nol A ex­po­sure had high­er cy­to­meg­a­lo­vir­us an­ti­body lev­els, “which sug­gests their cell-mediated im­mune sys­tem may not be func­tion­ing prop­er­ly,” said Er­in Rees Clay­ton, re­search in­ves­ti­ga­tor at the school and a mem­ber of the in­ves­ti­ga­tive team.

Re­search­ers al­so found that peo­ple age 18 and un­der with high­er lev­els of tri­clo­san were more likely to re­port di­ag­no­sis of al­ler­gies and hay fe­ver. There’s grow­ing con­cern among the sci­en­tif­ic com­mun­ity and con­sum­er groups that these endocrine-disrupting com­pounds are dan­ger­ous at low­er lev­els than pre­vi­ously thought, some sci­en­tists said.

As an an­ti­mi­cro­bi­al agent found in many house­hold prod­ucts, tri­clo­san may play a role in chang­ing the micro-organisms to which we are ex­posed in such a way that our im­mune sys­tem de­vel­op­ment in child­hood is af­fected, Aiello said.

“It is pos­si­ble that a per­son can be too clean for their own good,” he added, though it could al­so be that peo­ple “who have an al­ler­gy are more hy­gien­ic be­cause of their con­di­tion.” He not­ed that pre­vi­ous an­i­mal stud­ies in­di­cat­ed the two chem­i­cals un­der con­sid­era­t­ion may af­fect the im­mune sys­tem.

One sur­prise find­ing is that with Bi­sphe­nol A ex­po­sure, age seems to mat­ter, said Rees Clay­ton. In peo­ple 18 or old­er, high­er amounts of the com­pound were as­so­ci­at­ed with high­er cy­to­meg­a­lo­vir­us lev­els, but in peo­ple young­er than 18 the re­verse was true.

The re­search ap­pears on­line Nov. 30 in the jour­nal En­vi­ron­men­tal Health Per­spec­tives.

* * *

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Young people may suffer more allergies if they’re overexposed to antibacterial soaps containing a common ingredient, triclosan, a study indicates. The chemical is widely used in products such as antibacterial soaps, toothpaste, pens, diaper bags and medical devices. The scientists cautioned that their analysis didn’t clearly determine cause-and-effect relationships. For example, some people might use more antibacterial soaps because they have more allergies, rather than the other way around. But the triclosan findings 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 of the University of Michigan School of Public Health, principal investigator in the study. The research also found that excess exposure to Bisphenol A, a substance found in many plastics and as a protective lining in food cans, among adults may weaken the immune system. Both chemicals are in a class of toxicants called endocrine-disrupting compounds, thought to affect health by mimicking or acting on human hormones, said the researchers. The analysis used data from 2003 to 2006 generated by a previous U.S. study known as the National Health and Nutrition Examination Survey. The researchers compared urinary Bisphenol A and triclosan levels with diagnosis of allergies and with levels of antibodies to the pathogen cytomegalovirus, types of data considered markers of immune system changes. People over age 18 with higher levels of Bisphenol A exposure had higher cytomegalovirus antibody levels, “which suggests their cell-mediated immune system may not be functioning properly,” said Erin Rees Clayton, research investigator at school and a member of the investigative team. Researchers also found that people age 18 and under with higher levels of triclosan were more likely to report diagnosis of allergies and hay fever. There’s growing concern among the scientific community and consumer groups that these endocrine-disrupting compounds are dangerous at lower levels than previously thought, some scientists said. As an antimicrobial agent found in many household products, triclosan may play a role in changing the micro-organisms to which we are exposed in such a way that our immune system development in childhood is affected, Aiello said. “It is possible that a person can be too clean for their own good,” he added, though it could also be that people “who have an allergy are more hygienic because of their condition.” He noted that previous animal studies indicated the two chemicals under consideration may may affect the immune system. One surprise finding is that with Bisphenol A exposure, age seems to matter, said Rees Clayton. In people 18 or older, higher amounts of the compound were associated with higher cytomegalovirus levels, but in people younger than 18 the reverse was true. The research appears online Nov. 30 in the journal Environmental Health Perspectives.