Study Examines Popular Belief: Excessive Hygiene Causes Allergies? Are you joking? Are you serious?

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Excessive hygiene in wealthy industrialized countries may not be a major cause of allergies, a team of researchers explains. In experiments with mice, animals kept germ-free showed no more allergic reactions (for example, to house dust mites) than mice exposed to a wide variety of microbes from birth.

The study was published in the journal “Science Immunology”. A team led by Jonathan Coquet and Susanne Nylen from the Karolinska Institute in Stockholm tested the so-called ‘hygiene hypothesis’ in mice. It is stated that early contact with various germs in childhood reduces the risk of later allergic diseases.

No advantage for “wild” mice

It is believed that this makes the immune system more tolerant and less likely to overreact when it comes into contact with, for example, dust mite feces and mugwort pollen. The researchers compared how germ-free laboratory mice and ‘wildling mice’ respond to allergic triggers. The wildling mice are genetically identical to conventional laboratory mice, but were transplanted as embryos into ‘wild’ mouse mothers, carried and born by them. As a result, they came into contact with all kinds of microbes at an early age.

The wildlings’ immune systems responded just as strongly to the tests as those of the ‘pure’ laboratory mice. When exposed to allergens, the wildlings also showed “strong signs of pathogenic inflammatory responses and allergic immune responses,” the specialized publication said. Despite being colonized with natural microorganisms, they were not immune to allergic reactions.

“So you can’t just say: a dirty lifestyle stops allergies and cleanliness causes them,” Coquet told Science Immunology. This may be possible in special cases, but this is probably not a general rule. “Our research shows that general and widespread exposure to microbes may not have the clear positive effects we would like,” says Nylen.

According to researchers not involved in the study, the test results cannot completely disprove the hygiene hypothesis. In immunological studies it should always be clearly emphasized that the immune response is different in mice and humans. (SDA/bab)

Source: Blick