Before modern hygiene and housing standards, children died in droves of infections in the West. Now few do, but instead they are increasingly bothered by allergies, which are immune-system malfunctions. The current view among researchers is that there is a connection here. Live in dirt, and you will get infections that may kill you, but you won’t get allergies.

The Skeptikerpodden podcast has an interesting interview with bacteriologist Agnes Wold that touches upon about this issue. It made me wonder.

The kids who get allergies today: are they the ones who would have survived 200 years ago, or are they the ones who would have died? Or would there be no strong correlation between the outcomes if it could be tested?

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Comments

  1. #1 Greg
    February 4, 2011

    Here’s my anecdata: I grew up partly on a farm, surrounded by animals, dirt, dust, pollen, and mold. At age 4-6 I had terrible ear infections. If it wasn’t for modern medicine (Ventolin) I’m pretty sure I would have died before age 18, either from asthma provoked by airborne allergens, or by anaphylactic shock due to peanut/etc. ingestion.

    The argument that allergies have some protective value (especially in relation to parasites) seems reasonable to me. But there’s a very unhealthy downside! I suspect the trick is exposing people to enough varied immunological challenges to lessen their sentitivity, without provoking the kind of overreaction that leads to secondary health issues (infection/inflammation).

    I also believe that maternal exposure to peanuts during pregnancy is a major risk, although I’m not sure that current research conclusively supports this. My two sons, who don’t appear to have any serious allergies, were not exposed to maternal peanut proteins while in the womb.

  2. #2 Martin R
    February 4, 2011

    Agnes Wold emphasises that there are three very strong negative correlations with allergies: grow up a) under crowded conditions, b) among several siblings or in communal daycare, and/or c) around farm animals, and you will run a strongly decreased risk of becoming an allergic. All three factors also carry with them an increased risk of infections.

  3. #3 Art
    February 4, 2011

    Given that he major triggers for allergies, dust and pollen, are not generally considered a threat to human life I doubt allergies are useful adaptations or indicators of a population that has any survival advantages.

  4. #4 Martin R
    February 4, 2011

    These patients’ immune defences are hitting the dust and pollen because there are not enough real infections to teach them who the enemy is. I wonder if such an immune system, one that is prone to such trigger happiness, would be good or bad or indifferent to have if you lived in a cess pit in the Middle Ages.

  5. #5 Art
    February 4, 2011

    Given the narrowness of the immune response, you can be entirely immune to one germ but vulnerable to a related one, and the fact that immune response doesn’t seem to be a zero-sum game, you can get immunized for scores of diseases without overwhelming the ability to cope, I think that suffering from common allergies doesn’t have much bearing on your ability to survive the insults of a messier time.

    I also have my doubts as to exactly how much ‘cleaner’ we are. While kids get exposed to fewer infectious agents early in life, we are a better scrubbed people living in better scrubbed houses, once you get out into nature, where virtually everything is alive with microbes, the cleanliness seems far less apparent. In a way I suspect this is more aptly called a lack of exposure to nature. Let the kids run around the woods and roll around in the mud and they get exposure to a vast array of microbes.

    It also dawns on me that the nature of microbes have changed. Medieval kids were exposed daily to the rich microscopic stew but it was a local brew. Once the immune system had adapted to these usual suspects it was another hum-drum day playing in the muck. Modern kids are, by virtue of our modern transportation system, regularly exposed to stuff from thousands of miles away. Which suggests that while there is less total daily exposure to the usual suspects there is regular exposure to exotic, potentially unheralded and entirely unique, strains.

    I think there is something to the idea that a trigger-happy immune system may have advantages. Shoot everyone that gets within three meters of you, friend and foe alike, and you never have your pockets picked. Something to that. But as I understand it the immune system can’t afford to be too indiscriminate. Only fairly recently have we recognized auto-immune diseases. It can’t ‘shoot everything’. Even the very allergic have to have a fairly selective and well regulated immune systems. I suspect that any immune system that was sensitive enough to lend a significant advantage fighting off previously unknown major diseases would also tend to attack its host body.

    There is also the idea, suggested in a book on the Spanish flue epidemic in the early 1900s, that most people who died seemed to have died because of a massive overreaction by the body. The young, and healthy died faster than the very young and old. The deaths might be seen as a massive allergic reaction. I don’t know if it has ever been looked at, warrants some study, but it would be interesting to figure out if those with chronic seasonal allergies died more or less often than those without.

  6. #6 Nick W
    February 4, 2011

    I go swimming 3 times a week at a pool with a dirty changing room. I’m sure that the exposure to other people’s germs keeps my immune system healthy. The two occasions when I’ve been poorly recently have occurred when I’ve had a break from swimming.

  7. #7 becca
    February 4, 2011

    Today’s allergics are almost certainly yesterday’s survivors of ringworms and the like… the question is how *deadly* the worms are. More so than an average asthmatic, but less so than a crazy peanut allergy.
    It also probably extends past that. I think it’s entirely valid to view it as a *population* level thing and assume there is a huge advantage for humans as a species to have a mix of people who are trigger happy about a different types of immune assault, even if there is some individual fitness cost in ‘clean’ conditions.
    That said, exactly the hygiene hypothesis might play out for a given individual in this day and age, I won’t speculate on. But I’m pretty much on board with it exerting population effects over time.

  8. #8 History Blog
    February 4, 2011

    I wonder how the future doctors will view swine flu and hiv/aids in the future……

  9. #9 Pascvaks
    February 7, 2011

    T’would seem that filth at low (prehistoric)levels allows for antigen buildup and a higher level of allergic resistance. Filth at even lower (modern) levels allows for lower antigen buildup and greater suseptibility to allergic reactions. Filth at relatively high levels (prehistoric or modern), as always, tends to kill the vast majority of the least resistant.

  10. #10 Lars-Ake Larsson
    February 9, 2011

    Those interested might consider to read this article
    “About birch sap and pollen allergy” at
    http://www.cybis.se/craft/birch/index.php
    There is also an abstract available.
    Regards/Lars-Ake

  11. #11 TheBrummell
    February 9, 2011

    It depends on the correlation between general immune function and immune system overreaction.

    If greater general immune function is positively correlated with greater likelyhood of system overreaction, then today’s asthmatics / allergics / juvenile auto-immune disorder sufferers would have been the survivors of the middle ages – under this scenario, their highly active immune systems require a target-rich environment or they start zapping themselves.

    However, if the correlation is absent, then these same people would have been at least as likely to die as children in the pre-cleanliness era as anybody else; if you die at age 3 of a bacterial infection from drinking sewer water, you don’t show up as an allergic at age 9.

    I have no data to distinguish between these hypotheses, but I do suspect that at the population level the hygiene hypothesis is mostly correct, and that underexposure to potential infections during a critical phase (probably up to about age 5) is significantly correlated with the occurence of allergies and other erroneous immune responses at slightly later ages.

  12. #12 Martin R
    February 9, 2011

    According to the interview with professor Wold, it’s more like the first 6 months!

  13. #13 Riman Butterbur
    February 9, 2011

    A recent news report of a study of Egyptian mummies found that hardly any of them had died of cancer.

    I wondered when I read that, if the unhygenic conditions they lived in had strengthened their immune systems enough to put down rogue somatic cells.

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