experts estimate that many allergies and immune-system diseases have doubled, tripled or even quadrupled in the last few decades, depending on the ailment and country.Immune Systems Increasingly on Attack trots out the "hygiene hypothesis" again. I never found the argument that overly zealous housekeeping and parenting is to blame for immunological disorders very convincing.
The theory has also gained support from a variety of animal studies. One, for example, found that rats bred in a sterile laboratory had far more sensitive immune systems than those reared in the wild, where they were exposed to infections, microorganisms and parasites.Were the two groups of rats genetically identical? Perhaps lab rats come from genetically susceptible stock? After all, many lines of lab rats and mice were bred to be genetically susceptible to cancer; some forms of cancer are caused or exacerbated by immunological dysfunction.
"It's sort of a smoking gun of the hygiene hypothesis," said William Parker of Duke University.
Which lifestyle is more stressful for rats? The laboratory environment or the wild?
Why are inner-city kids, who experience higher exposures to rat and cockroach dander, more rather than less likely to suffer from asthma than suburban kids?
What about the Japanese studies that showed that asthma and cedar pollen allergies increased the most in children that were exposed to both higher cedar pollen AND ozone counts? Kids exposed to either/or did not experience the huge increases in allergies and asthma. (I wonder if anyone followed up with whether there is something uniquely irritating about ozone or if it is a proxy for general air pollution?)
Unlike William Parker, I don't see a "smoking gun" cause and effect there. I have an alternate explanation which I hope people will set out to disprove with well-designed scientific studies. What if, in the past, fewer people with genes that cause immune dysfunction survived to reproduce?
Anyway, I am not a physician and this is not my area of research. I am merely a scientist who suffers from serious immunological dysfunctions. Blame my mother's housekeeping standards, and you will get me riled up. Criticize my housekeeping standards and I am not responsible for what happens to you.
BTW, I did have an infestation of worms as a child. In Taiwan, where I spent some of my youth, "night soil" was used to fertilize the vegetables. Worms were common. Cockroaches were common, and humongous. So don't blame the lack of worms or cockroaches for the state of my immune system.