Can cleanliness increase the risk of allergies and asthma?

By Jacqueline Britz, National Center for Health Research

Why have allergies and asthma risen so dramatically in recent years?  From 1980 to 1994, asthma rates in the United States increased 75% overall, with rates increasing among individuals of all races, all age groups, and both sexes.  An especially disturbing increase in allergies, approximately 160%, was found for children under five.[1] About 70% of individuals with asthma also have allergies.[2] These statistics are very troubling, especially as asthma results in about 217,000 emergency room visits each year.[3]

There is clear evidence that children exposed to dirt and dust may be less likely to develop asthma and allergies.  In fact, some of the products we use to avoid germs, such as antibacterial soaps, hand sanitizers, and laundry detergents, may prevent the healthy development of a child’s immune system.  Experts say that during infancy and early childhood, the development of immunity is “derailed by the extremely clean household environments” that are found in many U.S. homes.[4] In other words, an environment that is “too clean” may not expose infants and young children to enough germs to adequately “educate” their developing immune system, and that may explain why so many children develop asthma or allergies.

Even for children living on farms, exposures to dirt and dust vary and that affects children’s health.  A study of Amish schoolchildren published in a major medical journal in 2016 found that because their farms do not use modern technology, only one in ten children have asthma or allergies.  That is about half as many as children in farming communities that use modern equipment.[8]

A recent study may shed light on the hygiene hypothesis and how chemicals may influence immune function.

Impact of Environmental Toxicants on Allergies and Immune Function

According to a new study by Dr. Erin Rees Clayton and her colleagues at the University of Michigan School of Public Health, young people with overexposure to antibacterial soaps containing triclosan may be at greater risk for suffering from allergies.[4] Further, overexposure to Bisphenol A (BPA) may weaken the immune system of adults.

Both of these chemicals belong to a class of toxicants known as endocrine-disrupting compounds. Often found in personal care and other consumer products, food, pharmaceuticals, and the environment, these compounds mimic or disrupt hormones.  What is particularly troubling about BPA and triclosan is that they are in many products that children and adults are exposed to regularly. Many plastics contain BPA, including those that line food and soft drink cans, as well as other products like dental sealants.  Triclosan is contained in antibacterial soaps, diaper bags, laundry detergents, toothpaste, pens, children’s toys, and medical devices to kill germs. Since triclosan was used as an antibacterial before the FDA required these chemicals to be approved, it has been used for more than 40 years prior to finally being reviewed for safety and effectiveness in 2013.  The results of FDA’s review have not yet been released.[5] As soaps, detergents, and toothpaste are used and go down the drain, triclosan is being washed into our lakes and rivers.[6]

A major concern about chemicals that disrupt hormones is that they could increase the risk of infertility, early puberty and other hormone-related problems in humans, including some cancers. While previous studies have researched the influence of BPA and triclosan on animals’ immune function, the Rees Clayton study was the first to investigate this relationship in humans. The study used data from the 2003-2006 National Health and Nutrition Examination Survey (NHANES) and looked at the relationship between urinary levels of BPA and triclosan and markers of how well the immune system functioned.  The markers used were the diagnoses of allergies or hayfever, and overall levels of a particular antibody in the blood called cytomegalovirus antibody.

The study included two age groups: participants over the age of 18 and participants between 6 and 18. Participants in the younger age group that had higher levels of triclosan were more likely to have been diagnosed with hayfever or allergies, which seems to support the hygiene hypothesis. While this same relationship was not seen with BPA, high levels of BPA exposure were associated with high antibody levels for those over age 18 (a sign of improper functioning of an immune response called the cell-mediated immune system).

The findings are interesting, but more research is needed to understand the link between allergies, hayfever, and triclosan.

Flu Infection May Help Prevent Asthma

With a similar interest in germs and asthma, Dr. Ya-Jen Chang and her colleagues, published in the Journal of Clinical Investigation, studied how the flu virus may later help prevent asthma.[7] In this study, active infectious flu agents were found to give mice protection against asthma only if the mice were exposed when they were young (2 weeks old). If the mice were exposed to flu when they were older, the exposure did not provide any protection against asthma. Researchers emphasized that this “influenza-induced protection” does not mean that we should expose people to dangerous infections in an effort to prevent asthma, but instead how this information may be helpful in the development of a new therapeutic strategy for treating asthma. One of the authors, Dale Umetsu, MD, PhD, a Professor of Pediatrics at Harvard Medical School, explains “If we can understand how infections prevent asthma, we may be able to replicate the good parts and avoid the bad parts of infection and develop new treatments for children to prevent asthma.”

To Be Clean or Not to Be Clean…

These research results don’t mean that exposure to germs is always good.  Germs spread disease, and regular hand-washing and other good hygiene habits will help prevent the spread of those germs. Nonetheless, the data suggest that using too many antibacterials may contribute to asthma and allergies, and that it can be beneficial to avoid over-exposure to products containing BPA and triclosan. There are many greener triclosan-free products, including sanitizers and disinfectants likeBurt’s Bees Aloe & Witch Hazel Hand Sanitizer, CleanWellFor My Kids, and Clean George. Some companies that provide canned food with BPA-free cans include Eden Foods and Vital Choice. While it is not realistic to avoid exposure to all chemicals, mindful consumers can reduce exposure to those thought to be particularly harmful.

All articles on our website have been approved by Dr. Diana Zuckerman and other senior staff.

This article was updated in 2016.


[1] Centers for Disease Control. Surveillance for Asthma – United States, 1960-1995, MMWR, 1998; 47 (SS-1).

[2] World Health Organization. Global surveillance, prevention and control of chronic respiratory diseases: a comprehensive approach, 2007.

[3] Pitts SR, Niska RW, Xu J, Burt CW. National Hospital Ambulatory Medical Care Survey: 2006 emergency department summary. National health statistics reports; no 7. Hyattsville, MD: National Center for Health Statistics. 2008.

[4] Rees Clayton, E. M., Todd, M., Dowd, J. B., & Aiello, A. E. (2010, November 29). The Impact of Bisphenol A and Triclosan on Immune Parameters in the US Population, NHANES 2003-2006. Environmental Health Perspectives.

[5] Asthma: The Hygiene Hypothesis. What do clean houses have in common with childhood infections? (2009, June 18). Retrieved from U.S. Food and Drug Administration website: http://www.fda.gov/biologicsbloodvaccines/resourcesforyou/consumers/ucm167471.htm

[6] Anger, C.T., et al.(2013, January 15). Quantification of triclosan, chlorinated triclosan derivatives, and their dioxin photoproducts in lacustrine sediment cores. Environmental Science and Technology.

[7] Chang, Y.-J., et al. (2011, January 4). Influenza infection in suckling mice expands an NKT cell subset that protects against airway hyperreactivity. Journal of Clinical Investigation, 121(1), 57-69. doi:10.1172/JCI44845

[8] Stein MM, Hrusch CL, et al., Innate Immunity and Asthma Risk in Amish and Hutterite Farm Children, The New England Journal of Medicine, 2016; 375:411-421.