Too Much of a Good Thing

Scott T. Weiss, MD Harvard Medical Schoo
lSpecial from Bottom Line's Daily Health News

Americans are admittedly, even proudly, obsessed with cleanliness. We bathe daily, use antibacterial soap to wash our hands and scour our homes with just about every germ-fighting product we can find.
By and large, living the clean life is good. Thanks primarily to improved personal hygiene and public sanitation, coupled with medical advances, such as the introduction of antibiotics and vaccinations, infectious diseases that once wreaked havoc on our health now have been largely vanquished.


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But it turns out that there might also be a downside to all this cleanliness and "bacteriophobia." In recent years, there has been a virtual epidemic in allergic diseases (sinusitis, asthma, etc.) and autoimmune diseases (such as multiple sclerosis, rheumatoid arthritis and type 1 diabetes). These diseases are most common in affluent, Western, industrialized societies, particularly the US.

THE HYGIENE HYPOTHESIS

One theory that has been proposed to explain this phenomenon is the hygiene hypothesis. According to Dr. Scott T. Weiss, professor of medicine at Harvard Medical School and associate physician at Brigham and Women's Hospital in Boston, the idea is that exposure early in life to microbes, such as bacteria and viruses, strengthens the developing immune system. As increased sanitation and cleaner lifestyles have reduced this exposure, the number of allergic and autoimmune diseases has risen.

STUDIES SUPPORT
THE HYGIENE HYPOTHESIS

The hygiene hypothesis was first put forth by epidemiologist E.P. Strachen in the late 1980s, when he noticed that older children were more likely to get hay fever than their younger siblings.
Today the results of a number of epidemiological studies support this theory, including...
Children in large families -- especially the younger siblings of brothers -- have fewer allergies than children in small families. Researchers speculate that as older children carry germs into the home, younger siblings' exposure to them builds immunity and provides protection from developing allergies.
Children from small families who attend day care before age one are less likely to develop allergies.
Children who receive oral antibiotics before age two are more likely to develop allergies. This is because the antibiotics that fight infection also kill beneficial bacteria that normally colonize the gastrointestinal tract. These harmless bacteria are important to normal immune system development early in life.
Hay fever is less common in children who live on farms. This is thought to be due to their exposure to endotoxins -- substances in certain bacteria that are most common in soil, the feces of farm animals and house dust.
Without stimulation early in life, the immune system may grow confused and strike out inappropriately. For example, now that intestinal parasites have been largely eliminated by modern sanitation, the immune system sometimes turns on itself and attacks the lining of the intestines, leading to inflammatory bowel disease. At the University of Iowa, mice deliberately infected with parasitic worms called helminthes were protected from inflammatory bowel disease. Now several human patients have also been treated -- successfully -- with a drink laced with eggs from a harmless pig whipworm.

WHAT YOU CAN DO

Eating dirt or moving to a farm are at best theoretical rather than practical clinical recommendations, notes Dr. Weiss in a New England Journal of Medicine editorial. However, he adds that a number of environmental factors are known to be associated with a lower incidence of allergic disease in early life. These include...
Having a dog or other pet in the home.
Attending day care in the first year of life.
Lactobacillus ruminus supplements. (Of course, consult your health-care professional before giving any supplement to a young child.)

SCIENTIFIC RESEARCH CONTINUES

Inspired by studies that support the hygiene hypothesis, researchers are working to create vaccines that imitate the immune effects of the microbes that cleanliness has brushed aside. The goal of these vaccines is to strengthen the body's immune defenses.
Scientists also are continuing to look at probiotics -- living cultures of beneficial bacteria, such as lactobacillus. Probiotics would ideally replace the beneficial bacteria that, in our quest for cleanliness, we have inadvertently suppressed or eliminated. More recent investigations have included prebiotics (substances and organisms which aid in the colonization of the 'friendly flora') and a more in-depth study of the evolution of a healthy microbial environment in newborns. It seems that these factors may be among the most important influences in protecting us from infections and limiting the severity and duration of them if they take hold.

LET THEM MAKE MUD PIES

Don't abandon the basic principles of good hygiene, but let your child play in the backyard and make all the messy mud pies he/she wants. And when you give her a bath afterward, plain old soap and water will do well.
Sources
Scott T. Weiss, MD, professor of medicine, Harvard Medical School and associate physician, Brigham and Women's Hospital, Boston.
US Food and Drug Administration, http://www.fda.gov/


First Printed: January 8, 2004