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The Hygiene Hypothesis — Is a Little Dirt Good for Your Child?

You may have heard the term human microbiome or microbiota, which refers to the thousands of species of microscopic organisms that inhabit the bodies of both healthy and diseased humans. These beneficial or “friendly” bacteria and fungi play vital roles in keeping us healthy and helping with normal processes such as digestion of the foods that we eat. Friendly flora can be found on our skins, in the skin’s deeper layers, our mouths, parts of our eyes, and our gastrointestinal tract.

Our bodies in fact contain 10 times as many cells from these organisms as human cells, even though the organism cells are much smaller than our body cells and as such, the combined weight and volume of these friendly pathogens is a lot smaller than the weight and volume of our cells.

So, bacteria and fungi are a part of life — 90 percent, to be exact. Our understanding of the crucial role that these organisms play in keeping us healthy has increased greatly in the last decade-plus. There are now volumes of medical texts describing the importance of bacteria and other allergens to our existence. One of the newer theories arising from the study of these friendly flora is the “Hygiene Hypothesis.”

This hypothesis states that a lack of infant and toddler exposure to infectious agents and friendly bacteria increases the risk of allergic diseases later on. The mechanism for this is not yet fully understood, but studies that have been done point to the validity of the hypothesis. The hygiene hypothesis has also been linked to the rise in autoimmune diseases and even asthma. And there is some evidence supporting the idea that disorders like autism may be explained by the hygiene hypothesis.

In 1963, Dr. David Poskanzer and his colleagues at Harvard University hypothesized that both multiple sclerosis and polio might be linked to an excessively high level of hygiene. In 1966, Uri Leibowitz and colleagues at Hadassah University in Israel concluded in a study that a greater and statistically significant number of Israeli children with access to treated drinking water, plumbing and fewer than two people per room developed M.S., compared to children who lived in less sanitary conditions.

In 1989, Dr. David Strachan reviewed data from more than 17 thousand British children born in March, 1958, comparing different social and environmental factors in an effort to find a correlation between the children’s environments and their risk of developing hay fever.

Strachan found that firstborn children had a 20.4 percent chance of developing hay fever; second-born children had a 15 percent chance; third-born children had a 12.5 percent chance; fourth-born children had a 10.6 percent chance; and fifth-born children had an 8.6 percent chance.

Children without siblings could not get exposed through them to bacteria and allergens. The doctor’s conclusion was that we need exposure to other people’s bacteria at an early age, to help strengthen our immune systems.

In 2008, a study by Dr. Chris Cardwell published in the journal Diabetologia found an increased risk for type 1 diabetes in children born by caesarean section. The study concluded that this was a result of not being exposed to natural bacteria in the course of birth.

The hygiene hypothesis has now expanded to include exposure to friendly bacteria and parasites as important developers of our immune system. In 2003, Dr. David Elliot, a gastroenterologist and immunologist at the University of Iowa, conducted a study in which 54 people with ulcerative colitis were given Trichuris (whipworm) eggs or a placebo. Forty-four percent of the people with the worm eggs improved significantly, while only 17 percent of the placebo group improved.

So, what are parents to do, in view of the hygiene hypothesis? It is still important to take basic sanitary measures — wash hands often; dispose of stagnant water; house cleaning, vacuuming and dusting should still be performed often. But the point that the hypothesis underlines is that exposing young children to different people, especially other infants and toddlers, and even having pets, can be a good way to strengthen your child’s immune system, and possibly reduce the chances of their contracting certain diseases later on.

By Lisa Pecos

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