Question:What is the 'hygiene hypothesis' as it relates to asthma and allergies?
Answer: Over the last 20 to 30 years there's been a progressive increase in asthma in most modern societies. And in trying to find an explanation for that, many investigators have looked at those populations who haven't had this increase. And it appears that it's less likely to increase in farm-based populations, in individuals who have more than one pet in the home, and in some cases in children who've been exposed to viral infection repeatedly early in life -- in other words, that for the rest of us who may not have these natural exposures, we've been too hygienic.
How can that cause asthma? And the answer may lie in the fact that we're not born with a mature immune system, that children's immune systems much like the rest of their body has to develop early in life. And if it's not challenged by a natural environment with exposures to infections, it may not develop normally, and so might become interested in being allergic to a cat, which obviously has no evolutionary advantage. And so the theory is that if we could find a way to train the immune system to develop normally with natural exposures, we might be able to inhibit the development of allergies and asthma.