From the WebMD Archives
Sept. 18, 2002 — Behind the ongoing epidemic of allergy and autoimmune disease there’s a surprising culprit: cleanliness.
One of the hallmarks of the 20th century was its war on germs. Kids now live in cleaner homes and suffer fewer infections than their grandparents did. There’s irony in this, according to the so-called “hygiene” theory. It holds that a germ-free childhood warps the immune system. This may lead not only to allergic diseases but also to autoimmune diseases such as type 1 diabetes and multiple sclerosis.
A report in the Sept. 19 issue of TheNew England Journal of Medicine now offers powerful support for this theory. The researchers carefully vacuumed up dust from the beds of 812 children from rural areas of Austria, Germany, and Switzerland. The dust was measured for a basic component of dirt — the outer cell wall of common bacteria, known to scientists as endotoxin. Also collected were the kids’ medical records.
The result: the kids who had the cleanest mattresses had the most hay fever, allergic asthma, and allergic reactions. The kids with the dirtiest beds — and least allergy and asthma — were most likely to live or play on farms. That’s no surprise, as earlier studies showed that children raised on farms have fewer allergies and less asthma than rural kids who don’t live on farms. Bacteria excreted by cows and other farm animals are the most common source of endotoxin.
These findings support previous research showing that having a cat or a dog in the home as a child or attending day care during the first year of life helps prevent the development of allergies and asthma in kids.
“Farm kids just have a natural environment, and this suggests that if you have natural exposure to endotoxin, it is helpful,” study leader Charlotte Braun-Fahrländer, MD, tells WebMD. “So should I have a pig in my garden? No. And this kind of study does not let us say that it would be helpful for your children to spend their holidays on a farm. It would be a nice, restful vacation. But I can’t say for sure it would help the children be more healthy.”
For the immune system to develop normally, it needs constant stimulation from the environment, says pediatric allergist Andrew H. Liu, MD, director of the training program at National Jewish Medical and Research Center in Denver.
“Allergies are a sort of deranged immune memory,” Liu tells WebMD. “If you look at people who are not allergic, their immune systems are reacting to the same things as people with allergies. They just remember to react in a way that does not cause allergic disease. So it seems that seeing a lot of things in the environment at an early age steers the immune system away from this type of deranged memory.”
There are two sides to this coin, warns Braun-Fahrländer, professor and vice-chairwoman of the Institute of Social and Preventive Medicine at the University of Basel in Switzerland.
“We have a very hygienic environment and we fear contact with dirt, but it doesn’t only harm us — it helps our immune system,” she says. “On the other hand, we have to be prudent because of course some [bacteria] have negative effects.”
It’s too soon to advise people to eat dirt or to move to a farm, says asthma expert Scott T. Weiss, MD, professor of medicine at Harvard Medical School. Weiss’ editorial accompanies the Braun-Fahrländer study.
“I think it would be a little too simple to say that how you clean your house is the issue here,” Weiss tells WebMD. “Nobody recommends keeping a pig or cow in the house. Whether you use Lysol or not isn’t going to significantly influence endotoxin levels. This study is a small step in a line of reasoning saying that exposures to bacteria and infections are important in developing a healthy immune system.”
This line of reasoning suggests that allergies may be just the tip of the iceberg, according to another NEJM article by Jean-François Bach, MD, DSc, director of the INSERM immunology unit at Necker Hospital in Paris. Bach suggests that improvements in public health that expose children to fewer infections increase their risk of autoimmune diseases such as type 1 diabetes, multiple sclerosis, Crohn’s disease, and perhaps even non-Hodgkin’s lymphoma.
Bach says that as the immune system develops in a child, it needs fine-tuning. Every time it fights a germ, it learns a little more. Eventually it learns the best way to fight germs and how not to start allergic or autoimmune reactions.
Parents should continue to protect their children from infections, Bach says. But he warns that overprotection — especially by unneeded antibiotic treatments — can kill off harmless bacteria that have much to teach the immune system.
“I think the first thing is not to worry if a child has a piece of meat falling on the ground and eats it,” Bach tells WebMD. “Exposure to some minor infections is not bad. You don’t need to sterilize and resterilize everything. The main thing is to avoid unnecessary antibiotic therapy.”
