Comment by dv_dt
8 hours ago
Hmm, I'm also wondering about studies about overly sanitized environments for children being correlated with higher allergy rates.
I guess poking around for a good representative study, it's actually low diversity of microbial exposure, not "cleaning" per-se that is correlated - e.g this is one reason why households with dogs have lower allergy rates. A monoculture of certain tree species also implies less microbial diversity.
I'd like to preemptively draw a line between two different kinds of hypothesis when it comes to hygiene:
1. The immune system is not being exposed enough to wild or even infectious content, and it needs more threats to fight off.
2. ("Old Friends") The immune system is not being exposed enough to commensal or even symbiotic organisms that we co-evolved with, throwing off its calibration and tuning.
I instinctively prefer the second, the first seems a little too simple, like some some scaled-down version of "tough love" and "spare the rod[-bacteria], spoil the child."
Regarding the second point: ...or parasitic.
There's a hypothesis that says the incidence of allergies correlates inversely with the incidence of certain common parasites, like the tapeworm or the pinworm. Additionally, nowadays pregnant women are advised to avoid getting infected with toxoplasmosis due to the birth defects it causes, but it wasn't until the 70s when the last route of transmission was found and explained.
What if the body is just looking for parasites where there are none?
EDIT: I also lean on the second, as the first doesn't explain why allergies can come and go seemingly without reason.
Personally currently I'm allergic to some unindentified plant and it's a different one than back when I was a child. Meanwhile my child is right now experiencing "my" childhood allergy season - with similar severity at that.
IIRC there has been scientists looking at what substances and pathways the parasites, particularly the helminths family, might affect because the parasites have a evolutionary "motivation" to suppress immune responses, at least to some degree in the host.
What if the human body's response to external influences (including parasites) is nuanced and complex?
What if the very idea of "parasite" is overly redactive: maybe there are both advantages and disadvantages of having another organism in your internal biome, in varying amounts?
An excellent distinction to make. Life however often says "Why not both? And 11 more you'd have never thought of. And one that seems impossible just for fun."
If it's possible, and it can force a function up a gradient, life is almost certainly doing it somewhere.
You might even say it finds a way.
I wonder why we focus so much on this claim, when there are many studies giving other plausible explanations.
> Living less than 75 m from the main road was significantly associated with lifetime allergic rhinitis (AR), past-year AR symptoms, diagnosed AR, and treated AR. The distance to the main road (P for trend=0.001), the length of the main road (P for trend=0.041), and the proportion of the main road area (P for trend=0.006) had an exposure-response relationship with allergic sensitization. A strong inverse association was observed between residential proximity to the main load and lung function, especially FEV1, FEV1/FVC, and FEF25-75.
Effect of Traffic-Related Air Pollution on Allergic Disease: Results of the Children's Health and Environmental Research - PMC - https://pmc.ncbi.nlm.nih.gov/articles/PMC4446634/
> The most serious issue might be the growing trend in sensitization to pollen, especially in urban settings (7, 8); in fact, people living near heavy traffic are affected with pollen-induced respiratory allergies more than those in rural districts (9). The sudden rise in environmental pollutant levels due to industrial development and urban motor vehicle traffic has affected air quality and consequently, the severity and mortality from allergic diseases (10). Some evidence suggests that air pollution might cause new cases of asthma as well (9, 11).
Interaction Between Air Pollutants and Pollen Grains: The Role on the Rising Trend in Allergy - https://pmc.ncbi.nlm.nih.gov/articles/PMC5941124/
This doesn't mean that exposure to biodiversity doesn't play a role, but when it comes to explaining the differences between rural and urban settings, this explanation seems more plausible to me than the hand-wavey claims about people supposedly cleaning their apartments more in cities.
Personally, I have seasonal asthma associated with pollen, since childhood, and I'm from a big city.
I have a much harder time walking next to a busy road in allergy season than being somewhere more rural, even when there are birch trees right in the vicinity of where I am, one of my allergenes.
It's not b/w of course though, the pollen can trigger it not only in the city. But then it's usually very mild.
My asthma is seasonal, allergy-associated, and still, the worst stressor I experience is pollution and car exhaust. Well, the worst unavoidable stressor.
Alcohol also seems to do bad things to my allergy response.
I think you're correct.
I live off on a city side street off of a major avenue in my city. Diesel soot looks (other than color) and behaves like pollen. Next week i'll be cleaning the pollen and soot particles from my porch. I personally don't suffer from allergies too bad (just headaches during peak pollen release), but my wife really does.
When I grew up in NYC, i was too young to remember allergies, but I can recall cubbies for inhalers as many of my classmates had asthma. We happened to be downwind from the Exxon refinery and Greenpoint garbage incinerator.
It can go the other direction, too: exposure to moldy home environments gave me (now resolved) food sensitivities, dust allergies, pet-associated allergies, etc.
You can definitely undertrain, or overwhelm, the immune system if not cautious!
Don't underestimate the amount of cockroach debris present in a modern home. There's a positive correlation between asthma and in-home roach population.
Maybe some plywood cheap old US homes full of holes or crevices, but here in Europe if you have cockroach infection and not blind or similarly disabled, you know it. They are not exactly hiding in the evening/night.