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Rural life may boost allergy resistance

Country dwellers richer in immune-calming bacteria

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4:15pm, May 7, 2012
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Children who grow up close to nature may have fewer allergies because of protective skin bacteria.

That finding is a new twist on the hygiene hypothesis, the idea that contact with bacteria early in life is crucial for the development of the human immune system. Skin microbes tied to the diversity of the natural environment seem to teach the body to calm allergic responses, researchers report online the week of May 7 in the Proceedings of the National Academy of Sciences.

“Here is yet another reason for planning green spaces in towns and cities,” says Ilkka Hanski, an ecologist at the University of Helsinki in Finland.

The decline of biodiversity in urban areas might damage the health of city dwellers by annihilating some of humankind’s tiniest allies, Hanski and his colleagues suggest. The researchers studied 118 Finnish adolescents who had lived their entire lives in a single place: a small town, a village or a house by itself in the countryside. Those teenagers who grew up near forests or farmland were less likely to have an allergic response when exposed to a cocktail of allergens.

Skin swabs revealed differences in the diversity of bacteria on the children’s skin. Life in more rural areas provided a richer variety of one kind of microbe called gammaproteobacteria.

This class of bug, found everywhere from the roots of plants to deep-sea hydrothermal vents, may be able to tinker with the immune system. In teenagers with more of the gammaproteobacteria Acinetobacter, blood cells contained more IL-10, an anti-inflammatory molecule that helps to block allergic responses.

“If what they’re looking at is a cause and not a consequence, it’s absolutely astonishing,” says Graham Rook, an immunologist at University College London. He points out that allergic responses could be changing the skin and its bacteria, instead of the other way around. Because the bacteria are probably inhaled and eaten as well, it’s also possible that they’re actually working in the gut, not on the skin.

Further studies of other human populations will be needed, says Rook, to see if the Finnish findings hold up elsewhere. Researchers don’t even know how the allegedly helpful bacteria transfer from the environment to the skin. Plants host bacteria on their leaves that might leapfrog to people. Or areas with lots of plant biodiversity might simply be healthy ecosystems in general, teeming with diverse microbes waiting to make contact.

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