Allergies and the Hygiene Hypothesis What is behind the rise in childhood allergies? One idea is that an emphasis on hygiene means we are no longer exposing children to enough bacteria to help trigger their natural immune systems.

Allergies and the Hygiene Hypothesis

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To find out why we hear so much these days about childhood allergies, we called Dr. Hugh Sampson, professor of pediatric allergy and immunology at Mount Sinai School of Medicine in New York.

First of all, Dr. Sampson, are there really more children who have peanut allergies now, or is this just a function of people are more aware of it, they are reporting it more often now?

Dr. HUGH SAMPSON (Mount Sinai School of Medicine): Well, I think people are more aware of it, but we've actually done a national survey looking at the prevalence of peanut allergy in the population. And one study was conducted in 1997, the second reported in 2002.

And what we found was that in the five-year time period between the two surveys, the prevalence of peanut allergy in children under the age of five, actually, doubled. So clearly there does seem to be an increase in the number of people with peanut allergy.

ELLIOTT: What is the explanation for that?

Dr. SAMPSON: We're not really sure. There are many theories as to what might be causing it. One is the so-called hygiene hypothesis, that we're not stimulating a portion of our immune system with bacteria and viral infections the way we used to.

There also appears to be something related to the type of diet we eat. The countries that are having problems with peanut allergy are all those where peanut butter, especially, is ingested. There is exposure to many of these foods, especially peanuts at earlier ages, because it's a highly nutritious, good tasting food...

ELLIOTT: And it's easy, speaking...

Dr. SAMPSON: And it's very easy.

ELLIOTT: a mother.

Dr. SAMPSON: Right. Absolutely. And even with - it has been shown that the peanut proteins are transmitted through maternal breast milk when mothers are ingesting peanut.

ELLIOTT: So let me just make sure I understand some of the possible explanations for this. When you say the hygiene hypothesis, that means that people are just too clean today?

Dr. SAMPSON: Right. We don't have the infections that we used to have. We've been immunized against many diseases, so your immune system has not been confronted with many of these different organisms. We've evolved over the centuries having to deal with all these infections and we do have what we call this primitive immune system or the innate immune system that is very much involved in the way we become tolerant to things in our environment. And without these other stimulations, this system may not be operating as it had in the past.

ELLIOTT: So if I, say, got the chicken pox or the measles, that may mean that I am less likely to be allergic to peanuts?

Dr. SAMPSON: I can't tell you for those specific infections, but that is the idea. We all have about two pounds of bacteria in our gastrointestinal tract, so we live with millions and millions of bacteria, you know, in a very harmonious relationship.

But because we don't get the exposure to some of the bacteria we had in the past, we may be making our self more susceptible to allergy.

ELLIOTT: Because of all the antibacterial lotions and soaps and things that we are...

Dr. SAMPSON: Right.

ELLIOTT: ...somewhat obsessed with these days?

Dr. SAMPSON: Right. You know, long ago, and I'm not saying we go back to this, but long ago children were not born in hospitals. We did not try to deliver them into sterile environments. They got the bacterial flora that was present in the house, which is very different than the kind of bacteria they encounter in the hospital.

ELLIOTT: Dr. Hugh Sampson is a professor of pediatric allergy and immunology at Mount Sinai School of Medicine in New York. Thank you for talking with us.

Dr. SAMPSON: Sure thing. Thank you.

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