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Hygiene Hypothesis Questioned

  • February 19, 2004

A new study questions the well-known hygiene hypothesis, which states that raising children in an overly clean environment leads to the development of asthma, as researchers found that infection with a flu virus increases the risk of developing allergic disease. The finding could undermine the key tenet of the hygiene hypothesis: that being infected with viruses protects against other diseases. However, others in the field say the paper does little to challenge the theory because:

  • It was known already that the respiratory viruses increase the risk
    of allergy development compared with the nonrespiratory viruses.
  • If a nonrespiratory virus had been used in the study it would likely yield a different response.
  • The animals in the study were the age-equivalent to young adults when infected with the flu virus, but the hygiene hypothesis generally states that exposures during the first year of life determine asthma or allergy later in life.

    The Scientist February 19, 2004