Why Your Kids' First Pet Should be a Dust Bunny

Health & Wellness on 06.06.11
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Photo credit: Chris Baskind/CC

One gram of soil contains 10 billion microbial cells. Does that have you reaching for a broom and dust pan? But consider this: over 90 percent of the cells in your body are also microbes, not human cells.

According to the "hygiene hypothesis," children who are exposed to less dirt and disease become more susceptible to immune system related disorders -- including asthma and allergies, Crohn's disease, and rheumatoid arthritis. The common-sense explanation implies that our bodies evolved to grow together with a daily inundation of both helpful and harmful microscopic beasties; when these assaults are lacking, our bodies misuse the immune system, activating sneezes or airway hyperactivity in response to attacks the body should perceive as harmless.

Scientists continue to chase down evidence and test the possible mechanisms to explain the big-picture observation that more cleanliness correlates to more autoimmune diseases. One very interesting avenue  of research, championed by Sharyn Clough, of Oregon State University, advocates comparing the socialization of boys versus girls to further explore the underlying relationship of hygiene to disease. Her philosophy rests on the observation that 9% of women suffer from asthma while only 6% of men have the condition; twice as many women have multiple sclerosis as men; three times as many suffer from rheumatism. Clough's conclusion: girls grow up cleaner, and the consequence is sickening. In her words:

"Girls tend to be dressed more in clothing that is not supposed to get dirty, girls tend to play indoors more than boys, and girl’s playtime is more often supervised by parents. There is a significant difference in the types and amounts of germs that girls and boys are exposed to, and this might explain some of the health differences we find between women and men.”

Erika von Mutius of the Ludwig-Maximilians University in Munich has a different opinion. She notes that the statistics on asthma are reversed in children: more boys suffer asthma than girls. Later onset of asthma in puberty or adulthood in females outpaces the new cases in males. Pointing out that women who handle a lot of cleaning products have a higher risk of asthma, von Mutius questions whether chemicals are to blame:

"Admittedly it is unclear, whether cleaning products contain chemicals that increase this risk, which is certainly conceivable, or whether it actually is an indirect effect, specifically that due to frequent cleaning there is less filth -- in the sense of the hygiene hypothesis -- and that raises the asthma risk."

The complexity of genetic and environmental interactions involved in these diseases makes proof of the hygiene hypothesis elusive. Scientists continue to look at the mechanisms involved, trying to find the environmental triggers that either activate or suppress immune reactions.

Until conclusive proof arrives, though, females everywhere can rejoice in testing the hypothesis themselves. Let your little girls chase frogs and dig in the dirt. Lay down your modern arsenal of cleaning chemicals, and join your daughters in a roll in the grass or across the carpet. Embrace the dust bunnies, they are proof that you do care about your family's welfare.


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