Good Hygiene, Bad Results?

Are Americans too clean? Proponents of the "hygiene hypothesis" argue that a societal emphasis on cleanliness has impaired the immune system's ability to respond as it was meant to. And that has left us open to other illnesses such as severe allergic reactions, gastrointestinal disorders, and autoimmune diseases.

"The evidence for all this is very, very powerful," says Graham A.W. Rook, M.D., at the University College London. "It's very easy to show if you live on a farm or keep a dog, you're less likely to have these disorders. If you are the youngest child in a big family, you're less likely to have these disorders."

Good hygiene has proved effective at protecting health, but an overzealous approach to cleanliness may have had unexpected results. Those who support the hygiene hypothesis believe that the human body adapted early on in evolution to bacteria, viruses, and other pathogens and began using them to "train" the immune system.

Wrong targets

"They are the police force that keeps the immune system from becoming trigger-happy," Dr. Rook says. "Basically, the immune system is now attacking things it shouldn't be attacking."

Illnesses and conditions that have been linked to the hygiene hypothesis include:

• Severe allergic reactions
• Inflammatory bowel disease, Crohn's disease, and other GI disorders
• Type 1 diabetes, multiple sclerosis, and other autoimmune disorders

Asthma and allergies

Mitchell H. Grayson, M.D., at the Medical College of Wisconsin, says the hygiene hypothesis has been most strongly linked to an increase in allergic diseases and asthma.

Bacteria in the environment teach an immune response to allergens that is more moderate and less severe. "In the absence of these bacteria, the immune system is thought to become more prone to allergic disease," Dr. Grayson says.

Benefits of good hygiene

Moderation seems to be the prudent approach to the situation. Abandoning good hygiene could cause a resurgence of public health diseases like dysentery or cholera.

"Public health and sanitation [have] been the single greatest improvement in our life expectancy," Dr. Grayson says. "I would not recommend living less cleanly."

Dr. Rook agrees. "We need to figure out how to replace what is good from the microbiological environment while maintaining the advances of good hygiene so we can get the best of both worlds."

Always talk with your health care provider to find out more information.