Wednesday, April 19, 2017

Your house may be too clean

Asthma free.
You are no doubt aware of the debate over how many germs are too many. Drop a child's pacifier on the floor -- do you pick it up and stick it back in or boil it? Dr. Perri Klass points out what this really means today:
When we talk about the hygiene hypothesis, the collection of theories that address the possible problems that can be associated with growing up less exposed to germs and dirt, we are essentially talking about growing up indoors. We’re talking about living in a world of relatively clean and controlled surfaces, where even small children who are constantly picking things up and putting them in their mouths are not going to come into contact with a very wide variety of exposures.
There’s no question that increasing hygiene has saved many children from sickness and death, he writes.
Scrupulously separating children from the microbes that can be found in impure water, for example, or unpasteurized milk has played a major role in reducing infant and child mortality, enabling millions of children to live and thrive. But we’ve also come to ask, in recent years, whether children who are too completely walled off from the microbial surroundings in which our species evolved may grow up with some negative consequences of our ever-cleaner homes.
Now that we're living indoors in suburbia what happens, says Maria Gloria Dominguez-Bello, an ecologist who is associate professor in the Human Microbiome Program at New York University School of Medicine, is this:
As houses become more enclosed and more subdivided, she said, spaces are increasingly separated by areas of use, and the speed at which outside air replaces inside air is decreased. “What happens is, we reduce the exposure to external environmental bacteria, so we become the main source of bacteria, our skin, our mouth, we shed bacteria, and the house becomes highly humanized, most of the bacteria in a house in a city will be human,” she said.
Walls, she said, are the best bystanders, revealing what is going on in a house, because they are not usually cleaned. After many years, she said, “you find highly oral bacteria near the sink,” fecal and vaginal bacteria “near the toilet,” and skin bacteria “in the rest of the house.”
“We used to live in much dustier environments,” said Marsha Wills-Karp, a professor of environmental health and engineering at the Bloomberg School of Public Health at Johns Hopkins University. 
Still, she said, though houses are cleaner, the built environment contains many components, including chemicals and airborne particles, not just microbes. 
“Studies have shown that priming or seeding of the microbiome in the child is absolutely critical,” she said. “While you don’t want to go out and expose your child to aggressive infections, you don’t want to create such a sterile environment that their immune system doesn’t develop normally; it puts them at risk of developing immune diseases.”
What's a mother to do? This article offers no strong guidelines. I think that's because this whole field is new, and nobody is quite sure what to do. Until then, do what you mother did: open the windows and let the kids play outside in the dirt.

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